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• AsyncWorker - a typesafe BackgroundWorker (and about Threading in general)

  generic methods enable typesafe Threading

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• Using delegates in C# (Part 2)

  - by rajbk

  Part 1 of this post can be read here. We are now about to see the different syntaxes for invoking a delegate and some c# syntactic sugar which allows you to code faster. We have the following console application. 1: public delegate double Operation(double x, double y); 2:  3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: Operation op1 = new Operation(Division); 9: double result = op1.Invoke(10, 5); 10: 11: Console.WriteLine(result); 12: Console.ReadLine(); 13: } 14: 15: static double Division(double x, double y) { 16: return x / y; 17: } 18: } Line 1 defines a delegate type called Operation with input parameters (double x, double y) and a return type of double. On Line 8, we create an instance of this delegate and set the target to be a static method called Division (Line 15) On Line 9, we invoke the delegate (one entry in the invocation list). The program outputs 5 when run. The language provides shortcuts for creating a delegate and invoking it (see line 9 and 11). Line 9 is a syntactical shortcut for creating an instance of the Delegate. The C# compiler will infer on its own what the delegate type is and produces intermediate language that creates a new instance of that delegate. Line 11 uses a a syntactical shortcut for invoking the delegate by removing the Invoke method. The compiler sees the line and generates intermediate language which invokes the delegate. When this code is compiled, the generated IL will look exactly like the IL of the compiled code above. 1: public delegate double Operation(double x, double y); 2:  3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: //shortcut constructor syntax 9: Operation op1 = Division; 10: //shortcut invoke syntax 11: double result = op1(10, 2); 12: 13: Console.WriteLine(result); 14: Console.ReadLine(); 15: } 16: 17: static double Division(double x, double y) { 18: return x / y; 19: } 20: } C# 2.0 introduced Anonymous Methods. Anonymous methods avoid the need to create a separate method that contains the same signature as the delegate type. Instead you write the method body in-line. There is an interesting fact about Anonymous methods and closures which won’t be covered here. Use your favorite search engine ;-)We rewrite our code to use anonymous methods (see line 9): 1: public delegate double Operation(double x, double y); 2:  3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: //Anonymous method 9: Operation op1 = delegate(double x, double y) { 10: return x / y; 11: }; 12: double result = op1(10, 2); 13: 14: Console.WriteLine(result); 15: Console.ReadLine(); 16: } 17: 18: static double Division(double x, double y) { 19: return x / y; 20: } 21: } We could rewrite our delegate to be of a generic type like so (see line 2 and line 9). You will see why soon. 1: //Generic delegate 2: public delegate T Operation<T>(T x, T y); 3:  4: public class Program 5: { 6: [STAThread] 7: static void Main(string[] args) 8: { 9: Operation<double> op1 = delegate(double x, double y) { 10: return x / y; 11: }; 12: double result = op1(10, 2); 13: 14: Console.WriteLine(result); 15: Console.ReadLine(); 16: } 17: 18: static double Division(double x, double y) { 19: return x / y; 20: } 21: } The .NET 3.5 framework introduced a whole set of predefined delegates for us including public delegate TResult Func<T1, T2, TResult>(T1 arg1, T2 arg2); Our code can be modified to use this delegate instead of the one we declared. Our delegate declaration has been removed and line 7 has been changed to use the Func delegate type. 1: public class Program 2: { 3: [STAThread] 4: static void Main(string[] args) 5: { 6: //Func is a delegate defined in the .NET 3.5 framework 7: Func<double, double, double> op1 = delegate (double x, double y) { 8: return x / y; 9: }; 10: double result = op1(10, 2); 11: 12: Console.WriteLine(result); 13: Console.ReadLine(); 14: } 15: 16: static double Division(double x, double y) { 17: return x / y; 18: } 19: } .NET 3.5 also introduced lambda expressions. A lambda expression is an anonymous function that can contain expressions and statements, and can be used to create delegates or expression tree types. We change our code to use lambda expressions. 1: public class Program 2: { 3: [STAThread] 4: static void Main(string[] args) 5: { 6: //lambda expression 7: Func<double, double, double> op1 = (x, y) => x / y; 8: double result = op1(10, 2); 9: 10: Console.WriteLine(result); 11: Console.ReadLine(); 12: } 13: 14: static double Division(double x, double y) { 15: return x / y; 16: } 17: } C# 3.0 introduced the keyword var (implicitly typed local variable) where the type of the variable is inferred based on the type of the associated initializer expression. We can rewrite our code to use var as shown below (line 7).  The implicitly typed local variable op1 is inferred to be a delegate of type Func<double, double, double> at compile time. 1: public class Program 2: { 3: [STAThread] 4: static void Main(string[] args) 5: { 6: //implicitly typed local variable 7: var op1 = (x, y) => x / y; 8: double result = op1(10, 2); 9: 10: Console.WriteLine(result); 11: Console.ReadLine(); 12: } 13: 14: static double Division(double x, double y) { 15: return x / y; 16: } 17: } You have seen how we can write code in fewer lines by using a combination of the Func delegate type, implicitly typed local variables and lambda expressions.

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• Metro: Creating an IndexedDbDataSource for WinJS

  - by Stephen.Walther

  The goal of this blog entry is to describe how you can create custom data sources which you can use with the controls in the WinJS library. In particular, I explain how you can create an IndexedDbDataSource which you can use to store and retrieve data from an IndexedDB database. If you want to skip ahead, and ignore all of the fascinating content in-between, I’ve included the complete code for the IndexedDbDataSource at the very bottom of this blog entry. What is IndexedDB? IndexedDB is a database in the browser. You can use the IndexedDB API with all modern browsers including Firefox, Chrome, and Internet Explorer 10. And, of course, you can use IndexedDB with Metro style apps written with JavaScript. If you need to persist data in a Metro style app written with JavaScript then IndexedDB is a good option. Each Metro app can only interact with its own IndexedDB databases. And, IndexedDB provides you with transactions, indices, and cursors – the elements of any modern database. An IndexedDB database might be different than the type of database that you normally use. An IndexedDB database is an object-oriented database and not a relational database. Instead of storing data in tables, you store data in object stores. You store JavaScript objects in an IndexedDB object store. You create new IndexedDB object stores by handling the upgradeneeded event when you attempt to open a connection to an IndexedDB database. For example, here’s how you would both open a connection to an existing database named TasksDB and create the TasksDB database when it does not already exist: var reqOpen = window.indexedDB.open(“TasksDB”, 2); reqOpen.onupgradeneeded = function (evt) { var newDB = evt.target.result; newDB.createObjectStore("tasks", { keyPath: "id", autoIncrement: true }); }; reqOpen.onsuccess = function () { var db = reqOpen.result; // Do something with db }; When you call window.indexedDB.open(), and the database does not already exist, then the upgradeneeded event is raised. In the code above, the upgradeneeded handler creates a new object store named tasks. The new object store has an auto-increment column named id which acts as the primary key column. If the database already exists with the right version, and you call window.indexedDB.open(), then the success event is raised. At that point, you have an open connection to the existing database and you can start doing something with the database. You use asynchronous methods to interact with an IndexedDB database. For example, the following code illustrates how you would add a new object to the tasks object store: var transaction = db.transaction(“tasks”, “readwrite”); var reqAdd = transaction.objectStore(“tasks”).add({ name: “Feed the dog” }); reqAdd.onsuccess = function() { // Tasks added successfully }; The code above creates a new database transaction, adds a new task to the tasks object store, and handles the success event. If the new task gets added successfully then the success event is raised. Creating a WinJS IndexedDbDataSource The most powerful control in the WinJS library is the ListView control. This is the control that you use to display a collection of items. If you want to display data with a ListView control, you need to bind the control to a data source. The WinJS library includes two objects which you can use as a data source: the List object and the StorageDataSource object. The List object enables you to represent a JavaScript array as a data source and the StorageDataSource enables you to represent the file system as a data source. If you want to bind an IndexedDB database to a ListView then you have a choice. You can either dump the items from the IndexedDB database into a List object or you can create a custom data source. I explored the first approach in a previous blog entry. In this blog entry, I explain how you can create a custom IndexedDB data source. Implementing the IListDataSource Interface You create a custom data source by implementing the IListDataSource interface. This interface contains the contract for the methods which the ListView needs to interact with a data source. The easiest way to implement the IListDataSource interface is to derive a new object from the base VirtualizedDataSource object. The VirtualizedDataSource object requires a data adapter which implements the IListDataAdapter interface. Yes, because of the number of objects involved, this is a little confusing. Your code ends up looking something like this: var IndexedDbDataSource = WinJS.Class.derive( WinJS.UI.VirtualizedDataSource, function (dbName, dbVersion, objectStoreName, upgrade, error) { this._adapter = new IndexedDbDataAdapter(dbName, dbVersion, objectStoreName, upgrade, error); this._baseDataSourceConstructor(this._adapter); }, { nuke: function () { this._adapter.nuke(); }, remove: function (key) { this._adapter.removeInternal(key); } } ); The code above is used to create a new class named IndexedDbDataSource which derives from the base VirtualizedDataSource class. In the constructor for the new class, the base class _baseDataSourceConstructor() method is called. A data adapter is passed to the _baseDataSourceConstructor() method. The code above creates a new method exposed by the IndexedDbDataSource named nuke(). The nuke() method deletes all of the objects from an object store. The code above also overrides a method named remove(). Our derived remove() method accepts any type of key and removes the matching item from the object store. Almost all of the work of creating a custom data source goes into building the data adapter class. The data adapter class implements the IListDataAdapter interface which contains the following methods: · change() · getCount() · insertAfter() · insertAtEnd() · insertAtStart() · insertBefore() · itemsFromDescription() · itemsFromEnd() · itemsFromIndex() · itemsFromKey() · itemsFromStart() · itemSignature() · moveAfter() · moveBefore() · moveToEnd() · moveToStart() · remove() · setNotificationHandler() · compareByIdentity Fortunately, you are not required to implement all of these methods. You only need to implement the methods that you actually need. In the case of the IndexedDbDataSource, I implemented the getCount(), itemsFromIndex(), insertAtEnd(), and remove() methods. If you are creating a read-only data source then you really only need to implement the getCount() and itemsFromIndex() methods. Implementing the getCount() Method The getCount() method returns the total number of items from the data source. So, if you are storing 10,000 items in an object store then this method would return the value 10,000. Here’s how I implemented the getCount() method: getCount: function () { var that = this; return new WinJS.Promise(function (complete, error) { that._getObjectStore().then(function (store) { var reqCount = store.count(); reqCount.onerror = that._error; reqCount.onsuccess = function (evt) { complete(evt.target.result); }; }); }); } The first thing that you should notice is that the getCount() method returns a WinJS promise. This is a requirement. The getCount() method is asynchronous which is a good thing because all of the IndexedDB methods (at least the methods implemented in current browsers) are also asynchronous. The code above retrieves an object store and then uses the IndexedDB count() method to get a count of the items in the object store. The value is returned from the promise by calling complete(). Implementing the itemsFromIndex method When a ListView displays its items, it calls the itemsFromIndex() method. By default, it calls this method multiple times to get different ranges of items. Three parameters are passed to the itemsFromIndex() method: the requestIndex, countBefore, and countAfter parameters. The requestIndex indicates the index of the item from the database to show. The countBefore and countAfter parameters represent hints. These are integer values which represent the number of items before and after the requestIndex to retrieve. Again, these are only hints and you can return as many items before and after the request index as you please. Here’s how I implemented the itemsFromIndex method: itemsFromIndex: function (requestIndex, countBefore, countAfter) { var that = this; return new WinJS.Promise(function (complete, error) { that.getCount().then(function (count) { if (requestIndex >= count) { return WinJS.Promise.wrapError(new WinJS.ErrorFromName(WinJS.UI.FetchError.doesNotExist)); } var startIndex = Math.max(0, requestIndex - countBefore); var endIndex = Math.min(count, requestIndex + countAfter + 1); that._getObjectStore().then(function (store) { var index = 0; var items = []; var req = store.openCursor(); req.onerror = that._error; req.onsuccess = function (evt) { var cursor = evt.target.result; if (index < startIndex) { index = startIndex; cursor.advance(startIndex); return; } if (cursor && index < endIndex) { index++; items.push({ key: cursor.value[store.keyPath].toString(), data: cursor.value }); cursor.continue(); return; } results = { items: items, offset: requestIndex - startIndex, totalCount: count }; complete(results); }; }); }); }); } In the code above, a cursor is used to iterate through the objects in an object store. You fetch the next item in the cursor by calling either the cursor.continue() or cursor.advance() method. The continue() method moves forward by one object and the advance() method moves forward a specified number of objects. Each time you call continue() or advance(), the success event is raised again. If the cursor is null then you know that you have reached the end of the cursor and you can return the results. Some things to be careful about here. First, the return value from the itemsFromIndex() method must implement the IFetchResult interface. In particular, you must return an object which has an items, offset, and totalCount property. Second, each item in the items array must implement the IListItem interface. Each item should have a key and a data property. Implementing the insertAtEnd() Method When creating the IndexedDbDataSource, I wanted to go beyond creating a simple read-only data source and support inserting and deleting objects. If you want to support adding new items with your data source then you need to implement the insertAtEnd() method. Here’s how I implemented the insertAtEnd() method for the IndexedDbDataSource: insertAtEnd:function(unused, data) { var that = this; return new WinJS.Promise(function (complete, error) { that._getObjectStore("readwrite").done(function(store) { var reqAdd = store.add(data); reqAdd.onerror = that._error; reqAdd.onsuccess = function (evt) { var reqGet = store.get(evt.target.result); reqGet.onerror = that._error; reqGet.onsuccess = function (evt) { var newItem = { key:evt.target.result[store.keyPath].toString(), data:evt.target.result } complete(newItem); }; }; }); }); } When implementing the insertAtEnd() method, you need to be careful to return an object which implements the IItem interface. In particular, you should return an object that has a key and a data property. The key must be a string and it uniquely represents the new item added to the data source. The value of the data property represents the new item itself. Implementing the remove() Method Finally, you use the remove() method to remove an item from the data source. You call the remove() method with the key of the item which you want to remove. Implementing the remove() method in the case of the IndexedDbDataSource was a little tricky. The problem is that an IndexedDB object store uses an integer key and the VirtualizedDataSource requires a string key. For that reason, I needed to override the remove() method in the derived IndexedDbDataSource class like this: var IndexedDbDataSource = WinJS.Class.derive( WinJS.UI.VirtualizedDataSource, function (dbName, dbVersion, objectStoreName, upgrade, error) { this._adapter = new IndexedDbDataAdapter(dbName, dbVersion, objectStoreName, upgrade, error); this._baseDataSourceConstructor(this._adapter); }, { nuke: function () { this._adapter.nuke(); }, remove: function (key) { this._adapter.removeInternal(key); } } ); When you call remove(), you end up calling a method of the IndexedDbDataAdapter named removeInternal() . Here’s what the removeInternal() method looks like: setNotificationHandler: function (notificationHandler) { this._notificationHandler = notificationHandler; }, removeInternal: function(key) { var that = this; return new WinJS.Promise(function (complete, error) { that._getObjectStore("readwrite").done(function (store) { var reqDelete = store.delete (key); reqDelete.onerror = that._error; reqDelete.onsuccess = function (evt) { that._notificationHandler.removed(key.toString()); complete(); }; }); }); } The removeInternal() method calls the IndexedDB delete() method to delete an item from the object store. If the item is deleted successfully then the _notificationHandler.remove() method is called. Because we are not implementing the standard IListDataAdapter remove() method, we need to notify the data source (and the ListView control bound to the data source) that an item has been removed. The way that you notify the data source is by calling the _notificationHandler.remove() method. Notice that we get the _notificationHandler in the code above by implementing another method in the IListDataAdapter interface: the setNotificationHandler() method. You can raise the following types of notifications using the _notificationHandler: · beginNotifications() · changed() · endNotifications() · inserted() · invalidateAll() · moved() · removed() · reload() These methods are all part of the IListDataNotificationHandler interface in the WinJS library. Implementing the nuke() Method I wanted to implement a method which would remove all of the items from an object store. Therefore, I created a method named nuke() which calls the IndexedDB clear() method: nuke: function () { var that = this; return new WinJS.Promise(function (complete, error) { that._getObjectStore("readwrite").done(function (store) { var reqClear = store.clear(); reqClear.onerror = that._error; reqClear.onsuccess = function (evt) { that._notificationHandler.reload(); complete(); }; }); }); } Notice that the nuke() method calls the _notificationHandler.reload() method to notify the ListView to reload all of the items from its data source. Because we are implementing a custom method here, we need to use the _notificationHandler to send an update. Using the IndexedDbDataSource To illustrate how you can use the IndexedDbDataSource, I created a simple task list app. You can add new tasks, delete existing tasks, and nuke all of the tasks. You delete an item by selecting an item (swipe or right-click) and clicking the Delete button. Here’s the HTML page which contains the ListView, the form for adding new tasks, and the buttons for deleting and nuking tasks: <!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <title>DataSources</title> <!-- WinJS references --> <link href="//Microsoft.WinJS.1.0.RC/css/ui-dark.css" rel="stylesheet" /> <script src="//Microsoft.WinJS.1.0.RC/js/base.js"></script> <script src="//Microsoft.WinJS.1.0.RC/js/ui.js"></script> <!-- DataSources references --> <link href="indexedDb.css" rel="stylesheet" /> <script type="text/javascript" src="indexedDbDataSource.js"></script> <script src="indexedDb.js"></script> </head> <body> <div id="tmplTask" data-win-control="WinJS.Binding.Template"> <div class="taskItem"> Id: <span data-win-bind="innerText:id"></span> <br /><br /> Name: <span data-win-bind="innerText:name"></span> </div> </div> <div id="lvTasks" data-win-control="WinJS.UI.ListView" data-win-options="{ itemTemplate: select('#tmplTask'), selectionMode: 'single' }"></div> <form id="frmAdd"> <fieldset> <legend>Add Task</legend> <label>New Task</label> <input id="inputTaskName" required /> <button>Add</button> </fieldset> </form> <button id="btnNuke">Nuke</button> <button id="btnDelete">Delete</button> </body> </html> And here is the JavaScript code for the TaskList app: /// <reference path="//Microsoft.WinJS.1.0.RC/js/base.js" /> /// <reference path="//Microsoft.WinJS.1.0.RC/js/ui.js" /> function init() { WinJS.UI.processAll().done(function () { var lvTasks = document.getElementById("lvTasks").winControl; // Bind the ListView to its data source var tasksDataSource = new DataSources.IndexedDbDataSource("TasksDB", 1, "tasks", upgrade); lvTasks.itemDataSource = tasksDataSource; // Wire-up Add, Delete, Nuke buttons document.getElementById("frmAdd").addEventListener("submit", function (evt) { evt.preventDefault(); tasksDataSource.beginEdits(); tasksDataSource.insertAtEnd(null, { name: document.getElementById("inputTaskName").value }).done(function (newItem) { tasksDataSource.endEdits(); document.getElementById("frmAdd").reset(); lvTasks.ensureVisible(newItem.index); }); }); document.getElementById("btnDelete").addEventListener("click", function () { if (lvTasks.selection.count() == 1) { lvTasks.selection.getItems().done(function (items) { tasksDataSource.remove(items[0].data.id); }); } }); document.getElementById("btnNuke").addEventListener("click", function () { tasksDataSource.nuke(); }); // This method is called to initialize the IndexedDb database function upgrade(evt) { var newDB = evt.target.result; newDB.createObjectStore("tasks", { keyPath: "id", autoIncrement: true }); } }); } document.addEventListener("DOMContentLoaded", init); The IndexedDbDataSource is created and bound to the ListView control with the following two lines of code: var tasksDataSource = new DataSources.IndexedDbDataSource("TasksDB", 1, "tasks", upgrade); lvTasks.itemDataSource = tasksDataSource; The IndexedDbDataSource is created with four parameters: the name of the database to create, the version of the database to create, the name of the object store to create, and a function which contains code to initialize the new database. The upgrade function creates a new object store named tasks with an auto-increment property named id: function upgrade(evt) { var newDB = evt.target.result; newDB.createObjectStore("tasks", { keyPath: "id", autoIncrement: true }); } The Complete Code for the IndexedDbDataSource Here’s the complete code for the IndexedDbDataSource: (function () { /************************************************ * The IndexedDBDataAdapter enables you to work * with a HTML5 IndexedDB database. *************************************************/ var IndexedDbDataAdapter = WinJS.Class.define( function (dbName, dbVersion, objectStoreName, upgrade, error) { this._dbName = dbName; // database name this._dbVersion = dbVersion; // database version this._objectStoreName = objectStoreName; // object store name this._upgrade = upgrade; // database upgrade script this._error = error || function (evt) { console.log(evt.message); }; }, { /******************************************* * IListDataAdapter Interface Methods ********************************************/ getCount: function () { var that = this; return new WinJS.Promise(function (complete, error) { that._getObjectStore().then(function (store) { var reqCount = store.count(); reqCount.onerror = that._error; reqCount.onsuccess = function (evt) { complete(evt.target.result); }; }); }); }, itemsFromIndex: function (requestIndex, countBefore, countAfter) { var that = this; return new WinJS.Promise(function (complete, error) { that.getCount().then(function (count) { if (requestIndex >= count) { return WinJS.Promise.wrapError(new WinJS.ErrorFromName(WinJS.UI.FetchError.doesNotExist)); } var startIndex = Math.max(0, requestIndex - countBefore); var endIndex = Math.min(count, requestIndex + countAfter + 1); that._getObjectStore().then(function (store) { var index = 0; var items = []; var req = store.openCursor(); req.onerror = that._error; req.onsuccess = function (evt) { var cursor = evt.target.result; if (index < startIndex) { index = startIndex; cursor.advance(startIndex); return; } if (cursor && index < endIndex) { index++; items.push({ key: cursor.value[store.keyPath].toString(), data: cursor.value }); cursor.continue(); return; } results = { items: items, offset: requestIndex - startIndex, totalCount: count }; complete(results); }; }); }); }); }, insertAtEnd:function(unused, data) { var that = this; return new WinJS.Promise(function (complete, error) { that._getObjectStore("readwrite").done(function(store) { var reqAdd = store.add(data); reqAdd.onerror = that._error; reqAdd.onsuccess = function (evt) { var reqGet = store.get(evt.target.result); reqGet.onerror = that._error; reqGet.onsuccess = function (evt) { var newItem = { key:evt.target.result[store.keyPath].toString(), data:evt.target.result } complete(newItem); }; }; }); }); }, setNotificationHandler: function (notificationHandler) { this._notificationHandler = notificationHandler; }, /***************************************** * IndexedDbDataSource Method ******************************************/ removeInternal: function(key) { var that = this; return new WinJS.Promise(function (complete, error) { that._getObjectStore("readwrite").done(function (store) { var reqDelete = store.delete (key); reqDelete.onerror = that._error; reqDelete.onsuccess = function (evt) { that._notificationHandler.removed(key.toString()); complete(); }; }); }); }, nuke: function () { var that = this; return new WinJS.Promise(function (complete, error) { that._getObjectStore("readwrite").done(function (store) { var reqClear = store.clear(); reqClear.onerror = that._error; reqClear.onsuccess = function (evt) { that._notificationHandler.reload(); complete(); }; }); }); }, /******************************************* * Private Methods ********************************************/ _ensureDbOpen: function () { var that = this; // Try to get cached Db if (that._cachedDb) { return WinJS.Promise.wrap(that._cachedDb); } // Otherwise, open the database return new WinJS.Promise(function (complete, error, progress) { var reqOpen = window.indexedDB.open(that._dbName, that._dbVersion); reqOpen.onerror = function (evt) { error(); }; reqOpen.onupgradeneeded = function (evt) { that._upgrade(evt); that._notificationHandler.invalidateAll(); }; reqOpen.onsuccess = function () { that._cachedDb = reqOpen.result; complete(that._cachedDb); }; }); }, _getObjectStore: function (type) { type = type || "readonly"; var that = this; return new WinJS.Promise(function (complete, error) { that._ensureDbOpen().then(function (db) { var transaction = db.transaction(that._objectStoreName, type); complete(transaction.objectStore(that._objectStoreName)); }); }); }, _get: function (key) { return new WinJS.Promise(function (complete, error) { that._getObjectStore().done(function (store) { var reqGet = store.get(key); reqGet.onerror = that._error; reqGet.onsuccess = function (item) { complete(item); }; }); }); } } ); var IndexedDbDataSource = WinJS.Class.derive( WinJS.UI.VirtualizedDataSource, function (dbName, dbVersion, objectStoreName, upgrade, error) { this._adapter = new IndexedDbDataAdapter(dbName, dbVersion, objectStoreName, upgrade, error); this._baseDataSourceConstructor(this._adapter); }, { nuke: function () { this._adapter.nuke(); }, remove: function (key) { this._adapter.removeInternal(key); } } ); WinJS.Namespace.define("DataSources", { IndexedDbDataSource: IndexedDbDataSource }); })(); Summary In this blog post, I provided an overview of how you can create a new data source which you can use with the WinJS library. I described how you can create an IndexedDbDataSource which you can use to bind a ListView control to an IndexedDB database. While describing how you can create a custom data source, I explained how you can implement the IListDataAdapter interface. You also learned how to raise notifications — such as a removed or invalidateAll notification — by taking advantage of the methods of the IListDataNotificationHandler interface.

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• Understanding the static keyword

  - by user985482

  I have some experience in developing with Java, Javascript and PHP. I am reading Microsoft Visual C# 2010 Step by Step which I feel it is a very good book on introducing you to the C# language. I seem to be having problems in understanding the static keyword. From what I understand this far if a class is declared static all methods and variable have to be static. The main method always is a static method so in the class that the main method exists all variables and methods are declared static if you have to call them in the main method. Also I have noticed that in order to call a static method from another class you do not need to create an object of that you can use the class name. What are the advantages of declaring static variables and methods? When should I declare static variable and methods?

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• Can a loosely typed language be considered true object oriented?

  - by user61852

  Can a loosely typed programming language like PHP be really considered object oriented? I mean, the methods don't have returning types and method parameters has no declared type either. Doesn't class design require methods to have a return type? Don't methods signatures have specifically-typed parameters? How can OOP techniques help you code in PHP if you always have to check the types of parameters received because the language doesn't enforce types? Please, if I'm wrong, explain it to me. When you design things using UML, then code classes in PHP with no return-typed methods and no-type parameters... Is the code really compliant with the UML design? You spend time designing the architecture of your software, then the compiler doesn't force the programmer to follow your design while coding, letting he/she assign any object variable to any other variable with no "type-mismatch" warning.

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• Is there a "golden ratio" in coding?

  - by badallen

  My coworkers and I often come up with silly ideas such as adding entries to Urban Dictionary that are inappropriate but completely make sense if you are a developer. Or making rap songs that are about delegates, reflections or closures in JS... Anyhow, here is what I brought up this afternoon which was immediately dismissed to be a stupid idea. So I want to see if I can get redemptions here. My idea is coming up with a Golden Ratio (or in the neighborhood of) between the number of classes per project versus the number of methods/functions per class versus the number of lines per method/function. I know this is silly and borderline, if not completely, useless, but just think of all the legacy methods or classes you have encountered that are absolutely horrid - like methods with 10000 lines or classes with 10000 methods. So Golden Ratio, anyone? :)

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• class hierarchy design for small java project

  - by user523956

  I have written a java code which does following:- Main goal is to fetch emails from (inbox, spam) folders and store them in database. It fetches emails from gmail,gmx,web.de,yahoo and Hotmail. Following attributes are stored in mysql database. Slno, messagedigest, messageid, foldername, dateandtime, receiver, sender, subject, cc, size and emlfile. For gmail,gmy and web.de, I have used javamail API, because email form it can be fetched with IMAP. For yahoo and hotmail, I have used html parser and httpclient to fetch emails form spam folder and for inbox folder, I have used pop3 javamail API. I want to have proper class hierarchy which makes my code efficient and easily reusable. As of now I have designed class hierarchy as below: I am sure it can still be improved. So I would like to have different opinions on it. I have following classes and methods as of now. MainController:- Here I pass emailid, password and foldername from which emails have to be fetched. Abstract Class :-EmailProtocol Abstract Methods of it (All methods except executeParser contains method definition):- connectImap() // used by gmx,gmail and web.de email ids connectPop3() // used by hotmail and yahoo to fetch emails of inbox folder createMessageDigest // used by every email provider(gmx, gmail,web.de,yahoo,hotmail) establishDBConnection // used by every email emailAlreadyExists // used by every email which checks whether email already exists in db or not, if not then store it. storeemailproperties // used by every email to store emails properties to mysql database executeParser // nothing written in it. Overwridden and used by just hotmail and yahoo to fetch emails form spam folder. Imap extends EmailProtocol (nothing in it. But I have to have it to access methods of EmailProtocol. This is used to fetch emails from gmail,gmx and web.de) I know this is really a bad way but don't know how to do it other way. Hotmsil extends EmailProtocol Methods:- executeParser() :- This is used by just hotmail email id. fetchjunkemails() :- This is also very specific for only hotmail email id. Yahoo extends EmailProtocol Methods:- executeParser() storeEmailtotemptable() MoveEmailtoInbox() getFoldername() nullorEquals() All above methods are specific for yahoo email id. public DateTimeFormat(class) format() //this formats datetime of gmax,gmail and web.de emails. formatYahoodate //this formats datetime of yahoo email. formatHotmaildate // this formats datetime of hotmail email. public StringFormat ConvertStreamToString() // Accessed by every class except DateTimeFormat class. formatFromTo() // Accessed by every class except DateTimeFormat class. public Class CheckDatabaseExistance public static void checkForDatabaseTablesAvailability() (This method checks at the beginnning whether database and required tables exist in mysql or not. if not it creates them) Please see code of my MainController class so that You can have an idea about how I use different classes. public class MainController { public static void main(String[] args) throws Exception { ArrayList<String> web_de_folders = new ArrayList<String>(); web_de_folders.add("INBOX"); web_de_folders.add("Unbekannt"); web_de_folders.add("Spam"); web_de_folders.add("OUTBOX"); web_de_folders.add("SENT"); web_de_folders.add("DRAFTS"); web_de_folders.add("TRASH"); web_de_folders.add("Trash"); ArrayList<String> gmx_folders = new ArrayList<String>(); gmx_folders.add("INBOX"); gmx_folders.add("Archiv"); gmx_folders.add("Entwürfe"); gmx_folders.add("Gelöscht"); gmx_folders.add("Gesendet"); gmx_folders.add("Spamverdacht"); gmx_folders.add("Trash"); ArrayList<String> gmail_folders = new ArrayList<String>(); gmail_folders.add("Inbox"); gmail_folders.add("[Google Mail]/Spam"); gmail_folders.add("[Google Mail]/Trash"); gmail_folders.add("[Google Mail]/Sent Mail"); ArrayList<String> pop3_folders = new ArrayList<String>(); pop3_folders.add("INBOX"); CheckDatabaseExistance.checkForDatabaseTablesAvailability(); EmailProtocol imap = new Imap(); System.out.println("CHECKING FOR NEW EMAILS IN WEB.DE...(IMAP)"); System.out.println("*********************************************************************************"); imap.connectImap("[email protected]", "pwd", web_de_folders); System.out.println("\nCHECKING FOR NEW EMAILS IN GMX.DE...(IMAP)"); System.out.println("*********************************************************************************"); imap.connectImap("[email protected]", "pwd", gmx_folders); System.out.println("\nCHECKING FOR NEW EMAILS IN GMAIL...(IMAP)"); System.out.println("*********************************************************************************"); imap.connectImap("[email protected]", "pwd", gmail_folders); EmailProtocol yahoo = new Yahoo(); Yahoo y=new Yahoo(); System.out.println("\nEXECUTING YAHOO PARSER"); System.out.println("*********************************************************************************"); y.executeParser("http://de.mc1321.mail.yahoo.com/mc/welcome?ymv=0","[email protected]","pwd"); System.out.println("\nCHECKING FOR NEW EMAILS IN INBOX OF YAHOO (POP3)"); System.out.println("*********************************************************************************"); yahoo.connectPop3("[email protected]","pwd",pop3_folders); System.out.println("\nCHECKING FOR NEW EMAILS IN INBOX OF HOTMAIL (POP3)"); System.out.println("*********************************************************************************"); yahoo.connectPop3("[email protected]","pwd",pop3_folders); EmailProtocol hotmail = new Hotmail(); Hotmail h=new Hotmail(); System.out.println("\nEXECUTING HOTMAIL PARSER"); System.out.println("*********************************************************************************"); h.executeParser("https://login.live.com/ppsecure/post.srf","[email protected]","pwd"); } } I have kept DatetimeFormat and StringFormat class public so that I can access its public methods by just (DatetimeFormat.formatYahoodate for e.g. from different methods). This is the first time I have developed something in java. It serves its purpose but of course code is still not so efficient I think. I need your suggestions on this project.

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• PostSharp, Obfuscation, and IL

  - by Simon Cooper

  Aspect-oriented programming (AOP) is a relatively new programming paradigm. Originating at Xerox PARC in 1994, the paradigm was first made available for general-purpose development as an extension to Java in 2001. From there, it has quickly been adapted for use in all the common languages used today. In the .NET world, one of the primary AOP toolkits is PostSharp. Attributes and AOP Normally, attributes in .NET are entirely a metadata construct. Apart from a few special attributes in the .NET framework, they have no effect whatsoever on how a class or method executes within the CLR. Only by using reflection at runtime can you access any attributes declared on a type or type member. PostSharp changes this. By declaring a custom attribute that derives from PostSharp.Aspects.Aspect, applying it to types and type members, and running the resulting assembly through the PostSharp postprocessor, you can essentially declare 'clever' attributes that change the behaviour of whatever the aspect has been applied to at runtime. A simple example of this is logging. By declaring a TraceAttribute that derives from OnMethodBoundaryAspect, you can automatically log when a method has been executed: public class TraceAttribute : PostSharp.Aspects.OnMethodBoundaryAspect { public override void OnEntry(MethodExecutionArgs args) { MethodBase method = args.Method; System.Diagnostics.Trace.WriteLine( String.Format( "Entering {0}.{1}.", method.DeclaringType.FullName, method.Name)); } public override void OnExit(MethodExecutionArgs args) { MethodBase method = args.Method; System.Diagnostics.Trace.WriteLine( String.Format( "Leaving {0}.{1}.", method.DeclaringType.FullName, method.Name)); } } [Trace] public void MethodToLog() { ... } Now, whenever MethodToLog is executed, the aspect will automatically log entry and exit, without having to add the logging code to MethodToLog itself. PostSharp Performance Now this does introduce a performance overhead - as you can see, the aspect allows access to the MethodBase of the method the aspect has been applied to. If you were limited to C#, you would be forced to retrieve each MethodBase instance using Type.GetMethod(), matching on the method name and signature. This is slow. Fortunately, PostSharp is not limited to C#. It can use any instruction available in IL. And in IL, you can do some very neat things. Ldtoken C# allows you to get the Type object corresponding to a specific type name using the typeof operator: Type t = typeof(Random); The C# compiler compiles this operator to the following IL: ldtoken [mscorlib]System.Random call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle( valuetype [mscorlib]System.RuntimeTypeHandle) The ldtoken instruction obtains a special handle to a type called a RuntimeTypeHandle, and from that, the Type object can be obtained using GetTypeFromHandle. These are both relatively fast operations - no string lookup is required, only direct assembly and CLR constructs are used. However, a little-known feature is that ldtoken is not just limited to types; it can also get information on methods and fields, encapsulated in a RuntimeMethodHandle or RuntimeFieldHandle: // get a MethodBase for String.EndsWith(string) ldtoken method instance bool [mscorlib]System.String::EndsWith(string) call class [mscorlib]System.Reflection.MethodBase [mscorlib]System.Reflection.MethodBase::GetMethodFromHandle( valuetype [mscorlib]System.RuntimeMethodHandle) // get a FieldInfo for the String.Empty field ldtoken field string [mscorlib]System.String::Empty call class [mscorlib]System.Reflection.FieldInfo [mscorlib]System.Reflection.FieldInfo::GetFieldFromHandle( valuetype [mscorlib]System.RuntimeFieldHandle) These usages of ldtoken aren't usable from C# or VB, and aren't likely to be added anytime soon (Eric Lippert's done a blog post on the possibility of adding infoof, methodof or fieldof operators to C#). However, PostSharp deals directly with IL, and so can use ldtoken to get MethodBase objects quickly and cheaply, without having to resort to string lookups. The kicker However, there are problems. Because ldtoken for methods or fields isn't accessible from C# or VB, it hasn't been as well-tested as ldtoken for types. This has resulted in various obscure bugs in most versions of the CLR when dealing with ldtoken and methods, and specifically, generic methods and methods of generic types. This means that PostSharp was behaving incorrectly, or just plain crashing, when aspects were applied to methods that were generic in some way. So, PostSharp has to work around this. Without using the metadata tokens directly, the only way to get the MethodBase of generic methods is to use reflection: Type.GetMethod(), passing in the method name as a string along with information on the signature. Now, this works fine. It's slower than using ldtoken directly, but it works, and this only has to be done for generic methods. Unfortunately, this poses problems when the assembly is obfuscated. PostSharp and Obfuscation When using ldtoken, obfuscators don't affect how PostSharp operates. Because the ldtoken instruction directly references the type, method or field within the assembly, it is unaffected if the name of the object is changed by an obfuscator. However, the indirect loading used for generic methods was breaking, because that uses the name of the method when the assembly is put through the PostSharp postprocessor to lookup the MethodBase at runtime. If the name then changes, PostSharp can't find it anymore, and the assembly breaks. So, PostSharp needs to know about any changes an obfuscator does to an assembly. The way PostSharp does this is by adding another layer of indirection. When PostSharp obfuscation support is enabled, it includes an extra 'name table' resource in the assembly, consisting of a series of method & type names. When PostSharp needs to lookup a method using reflection, instead of encoding the method name directly, it looks up the method name at a fixed offset inside that name table: MethodBase genericMethod = typeof(ContainingClass).GetMethod(GetNameAtIndex(22)); PostSharp.NameTable resource: ... 20: get_Prop1 21: set_Prop1 22: DoFoo 23: GetWibble When the assembly is later processed by an obfuscator, the obfuscator can replace all the method and type names within the name table with their new name. That way, the reflection lookups performed by PostSharp will now use the new names, and everything will work as expected: MethodBase genericMethod = typeof(#kGy).GetMethod(GetNameAtIndex(22)); PostSharp.NameTable resource: ... 20: #kkA 21: #zAb 22: #EF5a 23: #2tg As you can see, this requires direct support by an obfuscator in order to perform these rewrites. Dotfuscator supports it, and now, starting with SmartAssembly 6.6.4, SmartAssembly does too. So, a relatively simple solution to a tricky problem, with some CLR bugs thrown in for good measure. You don't see those every day!

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• Make a controller a superclass in MVC design pattern

  - by Nikola

  I am really confused how to handle this. I have: model.Outsider model.SubContractor (which extends Outsider) Basically, Outsider would mean Supplier, but SubContractor is not a Supplier itself so I had to divide it somehow. I used to have model.Outsider (super class of the two bellow) model.Supplier model.SubContractor But Supplier didn't have any unique fields so I have removed it (Was this correct?) So, continuing, I have db layer which has: db.DBOutsider db.DBSubContractor (which again extends the top one) And I have no place to put my Supplier methods. I can do that in DBOutsider, but then DBSubContractor (which extends DBOutsider) would get unnecessary methods. Do I create a DBSupplier even though there is no such class in the model layer? Then again, going to controller layer. It is the same situation as db layer. I have OutsiderController and SubContractorController (which extends the first one) (is this correct in first place? to have an extended controller?). But I have no place to put the methods which are concerned with Supplier and if I put them in the OutsiderController the SubContractorController would recieve unneccessary methods. At the moment I am going for the extra DBSupplier and SupplierController classes, but I have no idea if this is the correct way. Basically what perplexes me is the "empty" Supplier. Since it is supposed to be an Outsider but has no extra methods or fields, should there be an empty class?

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• Using Delegates in C# (Part 1)

  - by rajbk

  This post provides a very basic introduction of delegates in C#. Part 2 of this post can be read here. A delegate is a class that is derived from System.Delegate.  It contains a list of one or more methods called an invocation list. When a delegate instance is “invoked” with the arguments as defined in the signature of the delegate, each of the methods in the invocation list gets invoked with the arguments. The code below shows example with static and instance methods respectively: Static Methods 1: using System; 2: using System.Linq; 3: using System.Collections.Generic; 4: 5: public delegate void SayName(string name); 6: 7: public class Program 8: { 9: [STAThread] 10: static void Main(string[] args) 11: { 12: SayName englishDelegate = new SayName(SayNameInEnglish); 13: SayName frenchDelegate = new SayName(SayNameInFrench); 14: SayName combinedDelegate =(SayName)Delegate.Combine(englishDelegate, frenchDelegate); 15: 16: combinedDelegate.Invoke("Tom"); 17: Console.ReadLine(); 18: } 19: 20: static void SayNameInFrench(string name) { 21: Console.WriteLine("J'ai m'appelle " + name); 22: } 23: 24: static void SayNameInEnglish(string name) { 25: Console.WriteLine("My name is " + name); 26: } 27: } We have declared a delegate of type SayName with return type of void and taking an input parameter of name of type string. On line 12, we create a new instance of this delegate which refers to a static method - SayNameInEnglish.  SayNameInEnglish has the same return type and parameter list as the delegate declaration.  Once a delegate is instantiated, the instance will always refer to the same target. Delegates are immutable. On line 13, we create a new instance of the delegate but point to a different static method. As you may recall, a delegate instance encapsulates an invocation list. You create an invocation list by combining delegates using the Delegate.Combine method (there is an easier syntax as you will see later). When two non null delegate instances are combined, their invocation lists get combined to form a new invocation list. This is done in line 14.  On line 16, we invoke the delegate with the Invoke method and pass in the required string parameter. Since the delegate has an invocation list with two entries, each of the method in the invocation list is invoked. If an unhandled exception occurs during the invocation of one of these methods, the exception gets bubbled up to the line where the invocation was made (line 16). If a delegate is null and you try to invoke it, you will get a System.NullReferenceException. We see the following output when the method is run: My name is TomJ'ai m'apelle Tom Instance Methods The code below outputs the same results as before. The only difference here is we are creating delegates that point to a target object (an instance of Translator) and instance methods which have the same signature as the delegate type. The target object can never be null. We also use the short cut syntax += to combine the delegates instead of Delegate.Combine. 1: public delegate void SayName(string name); 2: 3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: Translator translator = new Translator(); 9: SayName combinedDelegate = new SayName(translator.SayNameInEnglish); 10: combinedDelegate += new SayName(translator.SayNameInFrench); 11:  12: combinedDelegate.Invoke("Tom"); 13: Console.ReadLine(); 14: } 15: } 16: 17: public class Translator { 18: public void SayNameInFrench(string name) { 19: Console.WriteLine("J'ai m'appelle " + name); 20: } 21: 22: public void SayNameInEnglish(string name) { 23: Console.WriteLine("My name is " + name); 24: } 25: } A delegate can be removed from a combination of delegates by using the –= operator. Removing a delegate from an empty list or removing a delegate that does not exist in a non empty list will not result in an exception. Delegates are invoked synchronously using the Invoke method. We can also invoke them asynchronously using the BeginInvoke and EndInvoke methods which are compiler generated.

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• Best Square Root Method (Precision VS Speed)

  Square Root Methods Fast Algorithm Speed Precision computational Quake3 Fast Square Root

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• PostSharp, Obfuscation, and IL

  - by Simon Cooper

  Aspect-oriented programming (AOP) is a relatively new programming paradigm. Originating at Xerox PARC in 1994, the paradigm was first made available for general-purpose development as an extension to Java in 2001. From there, it has quickly been adapted for use in all the common languages used today. In the .NET world, one of the primary AOP toolkits is PostSharp. Attributes and AOP Normally, attributes in .NET are entirely a metadata construct. Apart from a few special attributes in the .NET framework, they have no effect whatsoever on how a class or method executes within the CLR. Only by using reflection at runtime can you access any attributes declared on a type or type member. PostSharp changes this. By declaring a custom attribute that derives from PostSharp.Aspects.Aspect, applying it to types and type members, and running the resulting assembly through the PostSharp postprocessor, you can essentially declare 'clever' attributes that change the behaviour of whatever the aspect has been applied to at runtime. A simple example of this is logging. By declaring a TraceAttribute that derives from OnMethodBoundaryAspect, you can automatically log when a method has been executed: public class TraceAttribute : PostSharp.Aspects.OnMethodBoundaryAspect { public override void OnEntry(MethodExecutionArgs args) { MethodBase method = args.Method; System.Diagnostics.Trace.WriteLine( String.Format( "Entering {0}.{1}.", method.DeclaringType.FullName, method.Name)); } public override void OnExit(MethodExecutionArgs args) { MethodBase method = args.Method; System.Diagnostics.Trace.WriteLine( String.Format( "Leaving {0}.{1}.", method.DeclaringType.FullName, method.Name)); } } [Trace] public void MethodToLog() { ... } Now, whenever MethodToLog is executed, the aspect will automatically log entry and exit, without having to add the logging code to MethodToLog itself. PostSharp Performance Now this does introduce a performance overhead - as you can see, the aspect allows access to the MethodBase of the method the aspect has been applied to. If you were limited to C#, you would be forced to retrieve each MethodBase instance using Type.GetMethod(), matching on the method name and signature. This is slow. Fortunately, PostSharp is not limited to C#. It can use any instruction available in IL. And in IL, you can do some very neat things. Ldtoken C# allows you to get the Type object corresponding to a specific type name using the typeof operator: Type t = typeof(Random); The C# compiler compiles this operator to the following IL: ldtoken [mscorlib]System.Random call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle( valuetype [mscorlib]System.RuntimeTypeHandle) The ldtoken instruction obtains a special handle to a type called a RuntimeTypeHandle, and from that, the Type object can be obtained using GetTypeFromHandle. These are both relatively fast operations - no string lookup is required, only direct assembly and CLR constructs are used. However, a little-known feature is that ldtoken is not just limited to types; it can also get information on methods and fields, encapsulated in a RuntimeMethodHandle or RuntimeFieldHandle: // get a MethodBase for String.EndsWith(string) ldtoken method instance bool [mscorlib]System.String::EndsWith(string) call class [mscorlib]System.Reflection.MethodBase [mscorlib]System.Reflection.MethodBase::GetMethodFromHandle( valuetype [mscorlib]System.RuntimeMethodHandle) // get a FieldInfo for the String.Empty field ldtoken field string [mscorlib]System.String::Empty call class [mscorlib]System.Reflection.FieldInfo [mscorlib]System.Reflection.FieldInfo::GetFieldFromHandle( valuetype [mscorlib]System.RuntimeFieldHandle) These usages of ldtoken aren't usable from C# or VB, and aren't likely to be added anytime soon (Eric Lippert's done a blog post on the possibility of adding infoof, methodof or fieldof operators to C#). However, PostSharp deals directly with IL, and so can use ldtoken to get MethodBase objects quickly and cheaply, without having to resort to string lookups. The kicker However, there are problems. Because ldtoken for methods or fields isn't accessible from C# or VB, it hasn't been as well-tested as ldtoken for types. This has resulted in various obscure bugs in most versions of the CLR when dealing with ldtoken and methods, and specifically, generic methods and methods of generic types. This means that PostSharp was behaving incorrectly, or just plain crashing, when aspects were applied to methods that were generic in some way. So, PostSharp has to work around this. Without using the metadata tokens directly, the only way to get the MethodBase of generic methods is to use reflection: Type.GetMethod(), passing in the method name as a string along with information on the signature. Now, this works fine. It's slower than using ldtoken directly, but it works, and this only has to be done for generic methods. Unfortunately, this poses problems when the assembly is obfuscated. PostSharp and Obfuscation When using ldtoken, obfuscators don't affect how PostSharp operates. Because the ldtoken instruction directly references the type, method or field within the assembly, it is unaffected if the name of the object is changed by an obfuscator. However, the indirect loading used for generic methods was breaking, because that uses the name of the method when the assembly is put through the PostSharp postprocessor to lookup the MethodBase at runtime. If the name then changes, PostSharp can't find it anymore, and the assembly breaks. So, PostSharp needs to know about any changes an obfuscator does to an assembly. The way PostSharp does this is by adding another layer of indirection. When PostSharp obfuscation support is enabled, it includes an extra 'name table' resource in the assembly, consisting of a series of method & type names. When PostSharp needs to lookup a method using reflection, instead of encoding the method name directly, it looks up the method name at a fixed offset inside that name table: MethodBase genericMethod = typeof(ContainingClass).GetMethod(GetNameAtIndex(22)); PostSharp.NameTable resource: ... 20: get_Prop1 21: set_Prop1 22: DoFoo 23: GetWibble When the assembly is later processed by an obfuscator, the obfuscator can replace all the method and type names within the name table with their new name. That way, the reflection lookups performed by PostSharp will now use the new names, and everything will work as expected: MethodBase genericMethod = typeof(#kGy).GetMethod(GetNameAtIndex(22)); PostSharp.NameTable resource: ... 20: #kkA 21: #zAb 22: #EF5a 23: #2tg As you can see, this requires direct support by an obfuscator in order to perform these rewrites. Dotfuscator supports it, and now, starting with SmartAssembly 6.6.4, SmartAssembly does too. So, a relatively simple solution to a tricky problem, with some CLR bugs thrown in for good measure. You don't see those every day!

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• Are too many assertions code smell?

  - by Florents

  I've really fallen in love with unit testing and TDD - I am test infected. However, unit testing is used for public methods. Sometimes though I do have to test some assumptions-assertions in private methods too, because some of them are "dangerous" and refactoring can't help further. (I know, testing frameworks allo testing private methods). So, It became a habit of mine that (almost always) the first and the last line of a private method are both assertions. I guess this couldn't be bad (right ??). However, I've noticed that I also tend to use assertions in public methods too (as in the private) just "to be sure". Could this be "testing duplication" since the public method assumpotions are tested from the unit testng framework? Could someone think of too many assertions as a code smell?

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• PostSharp, Obfuscation, and IL

  - by simonc

  Aspect-oriented programming (AOP) is a relatively new programming paradigm. Originating at Xerox PARC in 1994, the paradigm was first made available for general-purpose development as an extension to Java in 2001. From there, it has quickly been adapted for use in all the common languages used today. In the .NET world, one of the primary AOP toolkits is PostSharp. Attributes and AOP Normally, attributes in .NET are entirely a metadata construct. Apart from a few special attributes in the .NET framework, they have no effect whatsoever on how a class or method executes within the CLR. Only by using reflection at runtime can you access any attributes declared on a type or type member. PostSharp changes this. By declaring a custom attribute that derives from PostSharp.Aspects.Aspect, applying it to types and type members, and running the resulting assembly through the PostSharp postprocessor, you can essentially declare 'clever' attributes that change the behaviour of whatever the aspect has been applied to at runtime. A simple example of this is logging. By declaring a TraceAttribute that derives from OnMethodBoundaryAspect, you can automatically log when a method has been executed: public class TraceAttribute : PostSharp.Aspects.OnMethodBoundaryAspect { public override void OnEntry(MethodExecutionArgs args) { MethodBase method = args.Method; System.Diagnostics.Trace.WriteLine( String.Format( "Entering {0}.{1}.", method.DeclaringType.FullName, method.Name)); } public override void OnExit(MethodExecutionArgs args) { MethodBase method = args.Method; System.Diagnostics.Trace.WriteLine( String.Format( "Leaving {0}.{1}.", method.DeclaringType.FullName, method.Name)); } } [Trace] public void MethodToLog() { ... } Now, whenever MethodToLog is executed, the aspect will automatically log entry and exit, without having to add the logging code to MethodToLog itself. PostSharp Performance Now this does introduce a performance overhead - as you can see, the aspect allows access to the MethodBase of the method the aspect has been applied to. If you were limited to C#, you would be forced to retrieve each MethodBase instance using Type.GetMethod(), matching on the method name and signature. This is slow. Fortunately, PostSharp is not limited to C#. It can use any instruction available in IL. And in IL, you can do some very neat things. Ldtoken C# allows you to get the Type object corresponding to a specific type name using the typeof operator: Type t = typeof(Random); The C# compiler compiles this operator to the following IL: ldtoken [mscorlib]System.Random call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle( valuetype [mscorlib]System.RuntimeTypeHandle) The ldtoken instruction obtains a special handle to a type called a RuntimeTypeHandle, and from that, the Type object can be obtained using GetTypeFromHandle. These are both relatively fast operations - no string lookup is required, only direct assembly and CLR constructs are used. However, a little-known feature is that ldtoken is not just limited to types; it can also get information on methods and fields, encapsulated in a RuntimeMethodHandle or RuntimeFieldHandle: // get a MethodBase for String.EndsWith(string) ldtoken method instance bool [mscorlib]System.String::EndsWith(string) call class [mscorlib]System.Reflection.MethodBase [mscorlib]System.Reflection.MethodBase::GetMethodFromHandle( valuetype [mscorlib]System.RuntimeMethodHandle) // get a FieldInfo for the String.Empty field ldtoken field string [mscorlib]System.String::Empty call class [mscorlib]System.Reflection.FieldInfo [mscorlib]System.Reflection.FieldInfo::GetFieldFromHandle( valuetype [mscorlib]System.RuntimeFieldHandle) These usages of ldtoken aren't usable from C# or VB, and aren't likely to be added anytime soon (Eric Lippert's done a blog post on the possibility of adding infoof, methodof or fieldof operators to C#). However, PostSharp deals directly with IL, and so can use ldtoken to get MethodBase objects quickly and cheaply, without having to resort to string lookups. The kicker However, there are problems. Because ldtoken for methods or fields isn't accessible from C# or VB, it hasn't been as well-tested as ldtoken for types. This has resulted in various obscure bugs in most versions of the CLR when dealing with ldtoken and methods, and specifically, generic methods and methods of generic types. This means that PostSharp was behaving incorrectly, or just plain crashing, when aspects were applied to methods that were generic in some way. So, PostSharp has to work around this. Without using the metadata tokens directly, the only way to get the MethodBase of generic methods is to use reflection: Type.GetMethod(), passing in the method name as a string along with information on the signature. Now, this works fine. It's slower than using ldtoken directly, but it works, and this only has to be done for generic methods. Unfortunately, this poses problems when the assembly is obfuscated. PostSharp and Obfuscation When using ldtoken, obfuscators don't affect how PostSharp operates. Because the ldtoken instruction directly references the type, method or field within the assembly, it is unaffected if the name of the object is changed by an obfuscator. However, the indirect loading used for generic methods was breaking, because that uses the name of the method when the assembly is put through the PostSharp postprocessor to lookup the MethodBase at runtime. If the name then changes, PostSharp can't find it anymore, and the assembly breaks. So, PostSharp needs to know about any changes an obfuscator does to an assembly. The way PostSharp does this is by adding another layer of indirection. When PostSharp obfuscation support is enabled, it includes an extra 'name table' resource in the assembly, consisting of a series of method & type names. When PostSharp needs to lookup a method using reflection, instead of encoding the method name directly, it looks up the method name at a fixed offset inside that name table: MethodBase genericMethod = typeof(ContainingClass).GetMethod(GetNameAtIndex(22)); PostSharp.NameTable resource: ... 20: get_Prop1 21: set_Prop1 22: DoFoo 23: GetWibble When the assembly is later processed by an obfuscator, the obfuscator can replace all the method and type names within the name table with their new name. That way, the reflection lookups performed by PostSharp will now use the new names, and everything will work as expected: MethodBase genericMethod = typeof(#kGy).GetMethod(GetNameAtIndex(22)); PostSharp.NameTable resource: ... 20: #kkA 21: #zAb 22: #EF5a 23: #2tg As you can see, this requires direct support by an obfuscator in order to perform these rewrites. Dotfuscator supports it, and now, starting with SmartAssembly 6.6.4, SmartAssembly does too. So, a relatively simple solution to a tricky problem, with some CLR bugs thrown in for good measure. You don't see those every day! Cross posted from Simple Talk.

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• The .NET 4.5 async/await Commands in Promise and Practice

  The .NET 4.5 async/await feature provides an opportunity for improving the scalability and performance of applications, particularly where tasks are more effectively done in parallel. The question is: do the scalability gains come at a cost of slowing individual methods? In this article Jon Smith investigates this issue by conducting a side-by-side evaluation of the standard synchronous methods and the new async methods in real applications.

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• Visual Tree Enumeration

  - by codingbloke

  I feel compelled to post this blog because I find I’m repeatedly posting this same code in silverlight and windows-phone-7 answers in Stackoverflow. One common task that we feel we need to do is burrow into the visual tree in a Silverlight or Windows Phone 7 application (actually more recently I found myself doing this in WPF as well).  This allows access to details that aren’t exposed directly by some controls.  A good example of this sort of requirement is found in the “Restoring exact scroll position of a listbox in Windows Phone 7”  question on stackoverflow.  This required that the scroll position of the scroll viewer internal to a listbox be accessed. A caveat One caveat here is that we should seriously challenge the need for this burrowing since it may indicate that there is a design problem.  Burrowing into the visual tree or indeed burrowing out to containing ancestors could represent significant coupling between module boundaries and that generally isn’t a good idea. Why isn’t this idea just not cast aside as a no-no?  Well the whole concept of a “Templated Control”, which are in extensive use in these applications, opens the coupling between the content of the visual tree and the internal code of a control.   For example, I can completely change the appearance and positioning of elements that make up a ComboBox.  The ComboBox control relies on specific template parts having set names of a specified type being present in my template.  Rightly or wrongly this does kind of give license to writing code that has similar coupling. Hasn’t this been done already? Yes it has.  There are number of blogs already out there with similar solutions.  In fact if you are using Silverlight toolkit the VisualTreeExtensions class already provides this feature.  However I prefer my specific code because of the simplicity principle I hold to.  Only write the minimum code necessary to give all the features needed.  In this case I add just two extension methods Ancestors and Descendents, note I don’t bother with “Get” or “Visual” prefixes.  Also I haven’t added Parent or Children methods nor additional “AndSelf” methods because all but Children is achievable with the addition of some other Linq methods.  I decided to give Descendents an additional overload for depth hence a depth of 1 is equivalent to Children but this overload is a little more flexible than simply Children. So here is the code:- VisualTreeEnumeration public static class VisualTreeEnumeration {     public static IEnumerable<DependencyObject> Descendents(this DependencyObject root, int depth)     {         int count = VisualTreeHelper.GetChildrenCount(root);         for (int i = 0; i < count; i++)         {             var child = VisualTreeHelper.GetChild(root, i);             yield return child;             if (depth > 0)             {                 foreach (var descendent in Descendents(child, --depth))                     yield return descendent;             }         }     }     public static IEnumerable<DependencyObject> Descendents(this DependencyObject root)     {         return Descendents(root, Int32.MaxValue);     }     public static IEnumerable<DependencyObject> Ancestors(this DependencyObject root)     {         DependencyObject current = VisualTreeHelper.GetParent(root);         while (current != null)         {             yield return current;             current = VisualTreeHelper.GetParent(current);         }     } }   Usage examples The following are some examples of how to combine the above extension methods with Linq to generate the other axis scenarios that tree traversal code might require. Missing Axis Scenarios var parent = control.Ancestors().Take(1).FirstOrDefault(); var children = control.Descendents(1); var previousSiblings = control.Ancestors().Take(1)     .SelectMany(p => p.Descendents(1).TakeWhile(c => c != control)); var followingSiblings = control.Ancestors().Take(1)     .SelectMany(p => p.Descendents(1).SkipWhile(c => c != control).Skip(1)); var ancestorsAndSelf = Enumerable.Repeat((DependencyObject)control, 1)     .Concat(control.Ancestors()); var descendentsAndSelf = Enumerable.Repeat((DependencyObject)control, 1)     .Concat(control.Descendents()); You might ask why I don’t just include these in the VisualTreeEnumerator.  I don’t on the principle of only including code that is actually needed.  If you find that one or more of the above  is needed in your code then go ahead and create additional methods.  One of the downsides to Extension methods is that they can make finding the method you actually want in intellisense harder. Here are some real world usage scenarios for these methods:- Real World Scenarios //Gets the internal scrollviewer of a ListBox ScrollViewer sv = someListBox.Descendents().OfType<ScrollViewer>().FirstOrDefault(); // Get all text boxes in current UserControl:- var textBoxes = this.Descendents().OfType<TextBox>(); // All UIElement direct children of the layout root grid:- var topLevelElements = LayoutRoot.Descendents(0).OfType<UIElement>(); // Find the containing `ListBoxItem` for a UIElement:- var container = elem.Ancestors().OfType<ListBoxItem>().FirstOrDefault(); // Seek a button with the name "PinkElephants" even if outside of the current Namescope:- var pinkElephantsButton = this.Descendents()     .OfType<Button>()     .FirstOrDefault(b => b.Name == "PinkElephants"); //Clear all checkboxes with the name "Selector" in a Treeview foreach (CheckBox checkBox in elem.Descendents()     .OfType<CheckBox>().Where(c => c.Name == "Selector")) {     checkBox.IsChecked = false; }   The last couple of examples above demonstrate a common requirement of finding controls that have a specific name.  FindName will often not find these controls because they exist in a different namescope. Hope you find this useful, if not I’m just glad to be able to link to this blog in future stackoverflow answers.

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• Go/Obj-C style interfaces with ability to extend compiled objects after initial release

  - by Skrylar

  I have a conceptual model for an object system which involves combining Go/Obj-C interfaces/protocols with being able to add virtual methods from any unit, not just the one which defines a class. The idea of this is to allow Ruby-ish open classes so you can take a minimalist approach to library development, and attach on small pieces of functionality as is actually needed by the whole program. Implementation of this involves a table of methods marked virtual in an RTTI table, which system functions are allowed to add to during module initialization. Upon typecasting an object to an interface, a Go-style lookup is done to create a vtable for that particular mapping and pass it off so you can have comparable performance to C/C++. In this case, methods may be added /afterwards/ which were not previously known and these new methods allow newer interfaces to be satisfied; while I like this idea because it seems like it would be very flexible (disregarding the potential for spaghetti code, which can happen with just about any model you use regardless). By wrapping the system calls for binding methods up in a set of clean C-compatible calls, one would also be able to integrate code with shared libraries and retain a decent amount of performance (Go does not do shared linking, and Objective-C does a dynamic lookup on each call.) Is there a valid use-case for this model that would make it worth the extra background plumbing? As much as this Dylan-style extensibility would be nice to have access to, I can't quite bring myself to a use case that would justify the overhead other than "it could make some kinds of code more extensible in future scenarios."

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• should I extend or create instance of the class

  - by meWantToLearn

  I have two classes Class A and Class B in Class A, i have three methods that perform the save, delete and select operation based upon the object I pass them. in Class B I perform the logic operations, such as modification to the property of the object before being passed to the methods of Class A, My problem is in Class B, should it extend Class A, and call the methods of class A , by parent::methodName or create instance of class A and then call Class A does not includes any property just methods. class A{ public function save($obj){ //code here } public function delete($obj){ //code here } public function select($obj){ //code here } } //Should I extend class A, and call the method by parent::methodName($obj) or create an instance of class A, call the method $instanceOfA-methodName($obj); class B extends A{ public function checkIfHasSaved($obj){ if($obj->saved == 'Yes'){ parent::save($obj); //**should I call the method like this** $instanceOFA = new A(); //**or create instance of class A and call without extending class A** instanceOFA->save($obj); } //other logic operations here } }

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• Automatic logging with Policy Injection Block, Structure Map, and log4net

  Log the entrance and exit of all methods in a project with minimal code clutter

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• Create simple jQuery plugin

  - by ybbest

  In the last post, I have shown you how to add the function to jQuery. In this post, I will show you how to create plugin to achieve this. 1. You need to wrap your code in the following construct, this is because you should not use $ directly as $ is global variable, it could have clash with some other library which also use $.Basically, you can pass in jQuery object into the function, so that $ is made available inside the function. (JavaScript use function to create scope, so you can make sure $ is referred to jQuery inside the function ) (function($){ //Your code goes here. }; })(jQuery); 2. Put your code into the construct above. (function ($) { $.getParameterByName = function (name) { name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]"); var regexS = "[\\?&]" + name + "=([^&#]*)"; var regex = new RegExp(regexS); var results = regex.exec(window.location.search); if (results == null) return ""; else return decodeURIComponent(results[1].replace(/\+/g, " ")); }; })(jQuery); 3. Now you can reference the code into you project and you can call the method in you JavaScript References: Provides scope for variables Variables are scoped at the function level in javascript. This is different to what you might be used to in a language like C# or Java where the variables are scoped to the block. What this means is if you declare a variable inside a loop or an if statement, it will be available to the entire function. If you ever find yourself needing to explicitly scope a variable inside a function you can use an anonymous function to do this. You can actually create an anonymous function and then execute it straight away and all the variables inside will be scoped to the anonymous function: (function() { var myProperty = "hello world"; alert(myProperty); })(); alert(typeof(myProperty)); // undefined How does an anonymous function in JavaScript work? Building Your First jQuery Plugin A Plugin Development Pattern

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• Is executing SQL through a WebService a really bad idea?

  - by Kyle

  Typically when creating a simple tool or something that has to use a database, I go through the fairly long process of first creating a webservice that connects to a database then creating methods on this webservice that do all the type of queries I need.. methods like List<Users> GetUsers() { ... } User GetUserByID(int id) { ... } //More Get/Update/Add/Delete methods Is it terrible design to simply make the webservice as secure as I can (not quite sure the way to do something like this yet) and just make a couple methods like this SqlDataReader RunQuery(string sql) { ... } void RunNonQuery(string sql) { ... } I would sorta be like exposing my database to the internet I suppose, which sounds bad but I'm not sure. I just feel like I waste so much time running everything through this webservice, there has to be a quicker yet safe way that doesn't involve my application connecting directly to the database (the application can't connect directly to database because the database isn't open to any connections but localhost, and where the appliction resides the standard sql ports are blocked anyway) Especially when I just need to run a few simple queries

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• Rendering design. How can I effectively deal with forward, deferred and transparent rendering?

  - by user1423893

  I have many objects in my game world that all derive from one base class. Each object will have different materials and will therefore be required to be drawn using various rendering techniques. I currently use the following order for rendering my objects. Deferred Forward Transparent (order independent) Each object has a rendering flag that denotes which one of the above methods should be used. The list of base objects in the scene are then iterated through and added to separate lists of deferred, forward or transparent objects based on their rendering flag value. The individual lists are then iterated through and drawn using the order above. Each list is cleared at the end of the frame. This methods works fairly well but it requires different draw methods for each material type. For example each object will require the following methods in order to be compatible with the possible flag settings. object.DrawDeferred() object.DrawForward() object.DrawTransparent() It is also hard to see where methods outside of materials, such as rendering shadow maps, would fit using this "flag & method" design. object.DrawShadow() I was hoping that someone may have some suggestions for improving this rendering process, possibly making it more generic and less verbose?

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• Native Browser Addin for Visual Studio

  Visual Studio 2005/2008 AddIn for browsing exported methods of native libraries

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• New EJB with ADF Tutorials and Demo

  Covering callback methods, queries and inheritance

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• Top 10 List of Vulnerabilities for Web Developers Released

  Injection, XSS at the top of the list Business - Polymers - Chemicals - Processing Methods - Molding

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