object state - Page 316

Silverlight binary serialization using Protobuf-net

how to serialize a pure .NET object classes to a fast binary data

Pattern for Accessing MySQL connection

We have an application which is C++ trying to access MySQL database. There are several (about 5 or so) threads in the application (with Boost library for threading) and in each thread has a few objects, each of which is trying to access Database for its' own purpose. It has a simple ORM kind of model but that really is not an important factor here. There are three potential access patterns i can think of: There could be single connection object per application or thread and is shared between all (or group). The object needs to be thread safe and there will be contentions but MySQL will not be fired with too many connections. Every object could initiate connection on its own. The database needs to take care of concurrency (which i think MySQL can) and the design could be much simpler. There could be two possibilities here. a. either object keeps a persistent connection for its life OR b. object initiate connection as and when needed. To simplify the contention as in case of 1 and not to create too many sockets as in case of 2, we can have group/set based connections. So there could be there could be more than one connection (say N), each of this connection could be shared connection across M objects. Naturally, each of the pattern has different resource cost and would work under different constraints and objectives. What criteria should i use to choose the pattern of this for my own application? What are some of the advantages and disadvantages of each of these pattern over the other? Are there any other pattern which is better? PS: I have been through these questions: mysql, one connection vs multiple and MySQL with mutiple threads and processes But they don't quite answer exactly what i am trying to ask.

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XML Manipulation with Apache AXIOM

Apache AXIOM (AXis2 Object Model) is a pull-based, XML Infoset-compliant object model that supports on-demand building of the object tree. Learn the basis of Axiom and how to use it.

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Render an image with separate layers for shadows/reflections in 3D Studio Max?

- by Bernd Plontsch

I have a scene with a simple object standing on a ground in the center. Caused by lights and the ground material there is some shadow and reflection on the ground surrounding the object. How can I render an image containing 3 separate layers for the object the ground the reflection / shadow on the ground Which format to use for this (it should include all 3 layers + I should be able to enable/disable them in Photoshop)? How do I define or prepare those layers for being rendering as image layers?

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WPF: Reloading app parts to handle persistence as well as memory management.

- by Ingó Vals

I created a app using Microsoft's WPF. It mostly handles data reading and input as well as associating relations between data within specific parameters. As a total beginner I made some bad design decision ( not so much decisions as using the first thing I got to work ) but now understanding WPF better I'm getting the urge to refactor my code with better design principles. I had several problems but I guess each deserves it's own question for clarity. Here I'm asking for proper ways to handle the data itself. In the original I wrapped each row in a object when fetched from database ( using LINQ to SQL ) somewhat like Active Record just not active or persistence (each app instance had it's own data handling part). The app has subunits handling different aspects. However as it was setup it loaded everything when started. This creates several problems, for example often it wouldn't be neccesary to load a part unless we were specifically going to work with that part so I wan't some form of lazy loading. Also there was problem with inner persistance because you might create a new object/row in one aspect and perhaps set relation between it and different object but the new object wouldn't appear until the program was restarted. Persistance between instances of the app won't be huge problem because of the small amount of people using the program. While I could solve this now using dirty tricks I would rather refactor the program and do it elegantly, Now the question is how. I know there are several ways and a few come to mind: 1) Each aspect of the program is it's own UserControl that get's reloaded/instanced everytime you navigate to it. This ensures you only load up the data you need and you get some persistancy. DB server located on same LAN and tables are small so that shouldn't be a big problem. Minor drawback is that you would have to remember the state of each aspect so you wouldn't always start at beginners square. 2) Having a ViewModel type object at the base level of the app with lazy loading and some kind of timeout. I would then propegate this object down the visual tree to ensure every aspect is getting it's data from the same instance 3) Semi active record data layer with static load methods. 4) Some other idea What in your opinion is the most practical way in WPF, what does MVVM assume?

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Powershell variables to string

- by Mike Koerner

I'm new to powershell. I'm trying to write an error handler to wrap around my script. Part of the error handler is dumping out some variable settings. I spent a while trying to do this and couldn't google a complete solution so I thought I'd post something. I want to display the $myinvocation variable. In powershell you can do this PS C:\> $myInvocation for my purpose I want to create a stringbuilder object and append the $myinvocation info. I tried this $sbOut = new-object System.Text.Stringbuilder $sbOut.appendLine($myinvocation) $sbOut.ToString() This produces Capacity MaxCapacity Length -------- ----------- ------ 86 2147483647 45 System.Management.Automation.InvocationInfo This is not what I wanted so I tried $sbOut.appendLine(($myinvocation|format-list *)) This produced Capacity MaxCapacity Length -------- ----------- ------ 606 2147483647 305 Microsoft.PowerShell.Commands.Internal.Format.FormatStartData Microsoft.PowerShell.Commands.Internal.Format.GroupStartData Micros oft.PowerShell.Commands.Internal.Format.FormatEntryData Microsoft.PowerShell.Commands.Internal.Format.GroupEndData Microsoft.Powe rShell.Commands.Internal.Format.FormatEndData Finally I figured out how to produce what I wanted: $sbOut = new-object System.Text.Stringbuilder [void]$sbOut.appendLine(($myinvocation|out-string)) $sbOut.ToString() MyCommand : $sbOut = new-object System.Text.Stringbuilder [void]$sbOut.appendLine(($myinvocation|out-string)) $sbOut.ToString() BoundParameters : {} UnboundArguments : {} ScriptLineNumber : 0 OffsetInLine : 0 HistoryId : 13 ScriptName : Line : PositionMessage : InvocationName : PipelineLength : 2 PipelinePosition : 1 ExpectingInput : False CommandOrigin : Runspace Note the [void] in front of the stringbuilder variable doesn't show the Capacity,MaxCapacity of the stringbuilder object. The pipe to out-string makes the output a string. It's not pretty but it works.

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Why MySQL sat for 2 minutes doing nothing?

- by Alex R

This was a one-time thing, not reproducible... But I saved the show innodb status output. Can anybody tell what's going on here? The simple insert took almost 3 minutes to complete. | InnoDB | | ===================================== 110201 15:58:10 INNODB MONITOR OUTPUT ===================================== Per second averages calculated from the last 34 seconds ---------- SEMAPHORES ---------- OS WAIT ARRAY INFO: reservation count 11963, signal count 11766 --Thread 1824 has waited at .\btr\btr0cur.c line 443 for 118.00 seconds the sema phore: S-lock on RW-latch at 09D6453C created in file .\buf\buf0buf.c line 550 a writer (thread id 1824) has reserved it in mode wait exclusive number of readers 1, waiters flag 1 Last time read locked in file .\buf\buf0flu.c line 599 Last time write locked in file .\btr\btr0cur.c line 443 Mutex spin waits 0, rounds 527817, OS waits 7133 RW-shared spins 2532, OS waits 1226; RW-excl spins 1652, OS waits 1118 ------------ TRANSACTIONS ------------ Trx id counter 0 95830 Purge done for trx's n:o < 0 95814 undo n:o < 0 0 History list length 11 LIST OF TRANSACTIONS FOR EACH SESSION: ---TRANSACTION 0 0, not started, OS thread id 3704 MySQL thread id 551, query id 2702112 localhost 127.0.0.1 root show innodb status ---TRANSACTION 0 95829, not started, OS thread id 3132 MySQL thread id 534, query id 2702020 localhost 127.0.0.1 root ---TRANSACTION 0 95828, not started, OS thread id 3152 MySQL thread id 527, query id 2701973 localhost 127.0.0.1 root ---TRANSACTION 0 95827, ACTIVE 118 sec, OS thread id 1824 inserting, thread decl ared inside InnoDB 500 mysql tables in use 1, locked 1 1 lock struct(s), heap size 320, 0 row lock(s) MySQL thread id 526, query id 2701972 localhost 127.0.0.1 root update INSERT INTO log_searchcriteria (userid,search_criteria,date,search_type) VALUES ( NAME_CONST('userid',NULL), NAME_CONST('search_criteria',_latin1' SELECT SQL_C ALC_FOUND_ROWS idx_search.CTCX_LATITUDE, idx_search.CTCX_LONGITUDE, idx_search.b uilding_id, idx_search.LN_LIST_NUMBER, idx_search.LP_LIST_PRICE, idx_search.HSN_ ADRESS_HOUSE_NUMBER, idx_search.STR_ADDRESS_STREET, idx_search.CP_ADDRESS_COMPAS S_POINT, idx_search.UN_UNIT, idx_search.CIT_CITY, idx_search.ZP_ZIP_CODE, idx_se arch.AR_AREA_NAME, idx_search.BR_BEDROOMS, idx_search.BTH_BATHS, idx_search.ST_S TATUS, idx_search.CTCX_STYLE_TYPE, idx_s -------- FILE I/O -------- I/O thread 0 state: wait Windows aio (insert buffer thread) I/O thread 1 state: wait Windows aio (log thread) I/O thread 2 state: wait Windows aio (read thread) I/O thread 3 state: wait Windows aio (write thread) Pending normal aio reads: 0, aio writes: 1, ibuf aio reads: 0, log i/o's: 0, sync i/o's: 0 Pending flushes (fsync) log: 0; buffer pool: 0 151006 OS file reads, 120758 OS file writes, 6844 OS fsyncs 0.00 reads/s, 0 avg bytes/read, 0.00 writes/s, 0.00 fsyncs/s ------------------------------------- INSERT BUFFER AND ADAPTIVE HASH INDEX ------------------------------------- Ibuf: size 1, free list len 5, seg size 7, 24664 inserts, 24664 merged recs, 4612 merges Hash table size 553253, node heap has 629 buffer(s) 0.00 hash searches/s, 0.00 non-hash searches/s --- LOG --- Log sequence number 5 2318193115 Log flushed up to 5 2318193115 Last checkpoint at 5 2318129891 0 pending log writes, 0 pending chkp writes 3036 log i/o's done, 0.00 log i/o's/second ---------------------- BUFFER POOL AND MEMORY ---------------------- Total memory allocated 213459462; in additional pool allocated 1720192 Dictionary memory allocated 240416 Buffer pool size 8192 Free buffers 0 Database pages 7563 Modified db pages 18 Pending reads 0 Pending writes: LRU 0, flush list 18, single page 0 Pages read 150973, created 28788, written 115137 0.00 reads/s, 0.00 creates/s, 0.00 writes/s No buffer pool page gets since the last printout -------------- ROW OPERATIONS -------------- 1 queries inside InnoDB, 0 queries in queue 1 read views open inside InnoDB Main thread id 2992, state: flushing buffer pool pages Number of rows inserted 794294, updated 89203, deleted 13698, read 1453084305 0.00 inserts/s, 0.00 updates/s, 0.00 deletes/s, 0.00 reads/s ---------------------------- END OF INNODB MONITOR OUTPUT ============================ Thanks

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When to use SOAP over REST

So, how does REST based services differ from SOAP based services, and when should you use SOAP? Representational State Transfer (REST) implements the standard HTTP/HTTPS as an interface allowing clients to obtain access to resources based on requested URIs. An example of a URI may look like this http://mydomain.com/service/method?parameter=var1&parameter=var2. It is important to note that REST based services are stateless because http/https is natively stateless. One of the many benefits for implementing HTTP/HTTPS as an interface is can be found in caching. Caching can be done on a web service much like caching is done on requested web pages. Caching allows for reduced web server processing and increased response times because content is already processed and stored for immediate access. Typical actions performed by REST based services include generic CRUD (Create, Read, Update, and Delete) operations and operations that do not require state. Simple Object Access Protocol (SOAP) on the other hand uses a generic interface in order to transport messages. Unlike REST, SOAP can use HTTP/HTTPS, SMTP, JMS, or any other standard transport protocols. Furthermore, SOAP utilizes XML in the following ways: Define a message Defines how a message is to be processed Defines the encoding of a message Lays out procedure calls and responses As REST aligns more with a Resource View, SOAP aligns more with a Method View in that business logic is exposed as methods typically through SOAP web service because they can retain state. In addition, SOAP requests are not cached therefore every request will be processed by the server. As stated before Soap does retain state and this gives it a special advantage over REST for services that need to preform transactions where multiple calls to a service are need in order to complete a task. Additionally, SOAP is more ideal for enterprise level services that implement standard exchange formats in the form of contracts due to the fact that REST does not currently support this. A real world example of where SOAP is preferred over REST can be seen in the banking industry where money is transferred from one account to another. SOAP would allow a bank to perform a transaction on an account and if the transaction failed, SOAP would automatically retry the transaction ensuring that the request was completed. Unfortunately, with REST, failed service calls must be handled manually by the requesting application. References: Francia, S. (2010). SOAP vs. REST. Retrieved 11 20, 2011, from spf13: http://spf13.com/post/soap-vs-rest Rozlog, M. (2010). REST and SOAP: When Should I Use Each (or Both)? Retrieved 11 20, 2011, from Infoq.com: http://www.infoq.com/articles/rest-soap-when-to-use-each

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introducing pointers to a large software project

- by stefan

I have a fairly large software project written in c++. In there, there is a class foo which represents a structure (by which i don't mean the programmers struct) in which foo-objects can be part of a foo-object. Here's class foo in simplest form: class Foo { private: std::vector<unsigned int> indices; public: void addFooIndex(unsigned int); unsigned int getFooIndex(unsigned int); }; Every foo-object is currently stored in an object of class bar. class Bar { private: std::vector<Foo> foos; public: void addFoo(Foo); std::vector<Foo> getFoos(); } So if a foo-object should represent a structure with a "inner" foo-object, I currently do Foo foo; Foo innerFoo; foo.addFooIndex(bar.getFoos().size() - 1); bar.addFoo(innerFoo); And to get it, I obviously use: Foo foo; for ( unsigned int i = 0; i < foo.getFooIndices().size(); ++i ) { Foo inner_foo; assert( foo.getFooIndices().at(i) < bar.getFoos().size() ); inner_foo = bar.getFoos().at(foo.getFooIndices().at(i)); } So this is not a problem. It just works. But it's not the most elegant solution. I now want to make the inner foos to be "more connected" with the foo-object. It would be obviously to change class foo to: class Foo { private: std::vector<Foo*> foo_pointers; public: void addFooPointer(Foo*); std::vector<Foo*> getFooPointers(); }; So now, for my question: How to gently change this basic class without messing up the whole code? Is there a "clean way"?

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consume a .net webservice using jQuery

- by Babunareshnarra

Implementation shows the way to consume web service using jQuery. The client side AJAX with HTTP POST request is significant when it comes to loading speed and responsiveness.Following is the service created that return's string in JSON.[WebMethod][ScriptMethod(ResponseFormat = ResponseFormat.Json)]public string getData(string marks){ DataTable dt = retrieveDataTable("table", @" SELECT * FROM TABLE WHERE MARKS='"+ marks.ToString() +"' "); List<object> RowList = new List<object>(); foreach (DataRow dr in dt.Rows) { Dictionary<object, object> ColList = new Dictionary<object, object>(); foreach (DataColumn dc in dt.Columns) { ColList.Add(dc.ColumnName, (string.Empty == dr[dc].ToString()) ? null : dr[dc]); } RowList.Add(ColList); } JavaScriptSerializer js = new JavaScriptSerializer(); string JSON = js.Serialize(RowList); return JSON;}Consuming the webservice $.ajax({ type: "POST", data: '{ "marks": "' + val + '"}', // This is required if we are using parameters contentType: "application/json", dataType: "json", url: "/dataservice.asmx/getData", success: function(response) { RES = JSON.parse(response.d); var obj = JSON.stringify(RES); } error: function (msg) { alert('failure'); }});Remember to reference jQuery library on the page.

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Multithreading: Communication from Parent thread to child thread

- by Dennis Nowland

I have a List of threads normally 3 threads each of the threads reference a webbrowser control that communicates with the parent control to populate a datagridview. What I need to do is when the user clicks the button in a datagridviewButtonCell corresponding data will be sent back to the webbrowser control within the child thread that originally communicated with the main thread. but when I try to do this I receive the following error message 'COM object that has been separated from its underlying RCW cannot be used.' my problem is that I can not figure out how to reference the relevant webbrowser control. I would appreciate any help that anyone can give me. The language used is c# winforms .Net 4.0 targeted Code sample: The following code is executed when user click on the Start button in the main thread private void StartSubmit(object idx) { /* method used by the new thread to initialise a 'myBrowser' inherited from the webbrowser control each submitters object is an a custom Control called 'myBrowser' which holds detail about the function of the object eg: */ //index: is an integer value which represents the threads id int index = (int)idx; //submitters[index] is an instance of the 'myBrowser' control submitters[index] = new myBrowser(); //threads integer id submitters[index]._ThreadNum = index; // naming convention used 'browser' +the thread index submitters[index].Name = "browser" + index; //set list in 'myBrowser' class to hold a copy of the list found in the main thread submitters[index]._dirs = dirLists[index]; // suppress and javascript errors the may occur in the 'myBrowser' control submitters[index].ScriptErrorsSuppressed = true; //execute eventHandler submitters[index].DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(DocumentCompleted); //advance to the next un-opened address in datagridview the navigate the that address //in the 'myBrowser' control. SetNextDir(submitters[index]); } private void btnStart_Click(object sender, EventArgs e) { // used to fill list<string> for use in each thread. fillDirs(); //connections is the list<Thread> holding the thread that have been opened //1 to 10 maximum for (int n = 0; n < (connections.Length); n++) { //initialise new thread to the StartSubmit method passing parameters connections[n] = new Thread(new ParameterizedThreadStart(StartSubmit)); // naming convention used conn + the threadIndex ie: 'conn1' to 'conn10' connections[n].Name = "conn" + n.ToString(); // due to the webbrowser control needing to be ran in the single //apartment state connections[n].SetApartmentState(ApartmentState.STA); //start thread passing the threadIndex connections[n].Start(n); } } Once the 'myBrowser' control is fully loaded I am inserting form data into webforms found in webpages loaded via data enter into rows found in the datagridview. Once a user has entered the relevant details into the different areas in the row the can then clicking a DataGridViewButtonCell that has tha collects the data entered and then has to be send back to the corresponding 'myBrowser' object that is found on a child thread. Thank you

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Which approach would lead to an API that is easier to use?

- by Clem

I'm writing a JavaScript API and for a particular case, I'm wondering which approach is the sexiest. Let's take an example: writing a VideoPlayer, I add a getCurrentTime method which gives the elapsed time since the start. The first approach simply declares getCurrentTime as follows: getCurrentTime():number where number is the native number type. This approach includes a CURRENT_TIME_CHANGED event so that API users can add callbacks to be aware of time changes. Listening to this event would look like the following: myVideoPlayer.addEventListener(CURRENT_TIME_CHANGED, function(evt){ console.log ("current time = "+evt.getDispatcher().getCurrentTime()); }); The second approach declares getCurrentTime differently: getCurrentTime():CustomNumber where CustomNumber is a custom number object, not the native one. This custom object dispatches a VALUE_CHANGED event when its value changes, so there is no need for the CURRENT_TIME_CHANGED event! Just listen to the returned object for value changes! Listening to this event would look like the following: myVideoPlayer.getCurrentTime().addEventListener(VALUE_CHANGED, function(evt){ console.log ("current time = "+evt.getDispatcher().valueOf()); }); Note that CustomNumber has a valueOf method which returns a native number that lets the returned CustomNumber object being used as a number, so: var result = myVideoPlayer.getCurrentTime()+5; will work! So in the first approach, we listen to an object for a change in its property's value. In the second one we directly listen to the property for a change on its value. There are multiple pros and cons for each approach, I just want to know which one the developers would prefer to use!

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Green (Screen) Computing

- by onefloridacoder

I recently was given an assignment to create a UX where a user could use the up and down arrow keys, as well as the tab and enter keys to move through a Silverlight datagrid that is going be used as part of a high throughput data entry UI. And to be honest, I’ve not trapped key codes since I coded JavaScript a few years ago. Although the frameworks I’m using made it easy, it wasn’t without some trial and error. The other thing that bothered me was that the customer tossed this into the use case as they were delivering the use case. Fine. I’ll take a whack at anything and beat up myself and beg (I’m not beyond begging for help) the community for help to get something done if I have to. It wasn’t as bad as I thought and I thought I would hopefully save someone a few keystrokes if you wanted to build a green screen for your customer. Here’s the ValueConverter to handle changing the strings to decimals and then back again. The value is a nullable valuetype so there are few extra steps to take. Usually the “ConvertBack()” method doesn’t get addressed but in this case we have two-way binding and the converter needs to ensure that if the user doesn’t enter a value it will remain null when the value is reapplied to the model object’s setter. 1: using System; 2: using System.Windows.Data; 3: using System.Globalization; 4: 5: public class NullableDecimalToStringConverter : IValueConverter 6: { 7: public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) 8: { 9: if (!(((decimal?)value).HasValue)) 10: { 11: return (decimal?)null; 12: } 13: if (!(value is decimal)) 14: { 15: throw new ArgumentException("The value must be of type decimal"); 16: } 17: 18: NumberFormatInfo nfi = culture.NumberFormat; 19: nfi.NumberDecimalDigits = 4; 20: 21: return ((decimal)value).ToString("N", nfi); 22: } 23: 24: public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) 25: { 26: decimal nullableDecimal; 27: decimal.TryParse(value.ToString(), out nullableDecimal); 28: 29: return nullableDecimal == 0 ? null : nullableDecimal.ToString(); 30: } 31: } The ConvertBack() method uses TryParse to create a value from the incoming string so if the parse fails, we get a null value back, which is what we would expect. But while I was testing I realized that if the user types something like “2..4” instead of “2.4”, TryParse will fail and still return a null. The user is getting “puuu-lenty” of eye-candy to ensure they know how many values are affected in this particular view. Here’s the XAML code. This is the simple part, we just have a DataGrid with one column here that’s bound to the the appropriate ViewModel property with the Converter referenced as well. 1: <data:DataGridTextColumn 2: Header="On-Hand" 3: Binding="{Binding Quantity, 4: Mode=TwoWay, 5: Converter={StaticResource DecimalToStringConverter}}" 6: IsReadOnly="False" /> Nothing too magical here. Just some XAML to hook things up. Here’s the code behind that’s handling the DataGridKeyup event. These are wired to a local/private method but could be converted to something the ViewModel could use, but I just need to get this working for now. 1: // Wire up happens in the constructor 2: this.PicDataGrid.KeyUp += (s, e) => this.HandleKeyUp(e); 1: // DataGrid.BeginEdit fires when DataGrid.KeyUp fires. 2: private void HandleKeyUp(KeyEventArgs args) 3: { 4: if (args.Key == Key.Down || 5: args.Key == Key.Up || 6: args.Key == Key.Tab || 7: args.Key == Key.Enter ) 8: { 9: this.PicDataGrid.BeginEdit(); 10: } 11: } And that’s it. The ValueConverter was the biggest problem starting out because I was using an existing converter that didn’t take nullable value types into account. Once the converter was passing back the appropriate value (null, “#.####”) the grid cell(s) and the model objects started working as I needed them to. HTH.

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Having trouble compiling UnrealScript with defaultproperties

- by Enchanter

Have just started scripting in Unreal Script and am following the instructions of the opening chapter of a book on the subject. I have set the development tools up as described in the book such that it is now possible to compile the scripts for UDK before adding them to a level. My issue is: the very first script the book asks you to compile is the following: class AwesomeActor extends Actor placeable; defaultproperties { Begin Object Class=SpriteComponent Name = Sprite Sprite = Texture2D'EditorResources.S_NavP' End Object Components.Add(Sprite) } And when I hit F9 in the compiler I get the following error message: Error, BEGIN OBJECT: Must specify valid name for suboject/copmponent: Begin Object class=SpriteComponent name = Sprite My question: As far as I'm aware I've copied the code from the book veribatim including capital and smaller case letters but I'm getting this error and I was wondering if anyone knew why and if so how I would fix it?

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Saving user details on OnSuspending event for Metro Style Apps

- by nmarun

I recently started getting to know about Metro Style Apps on Windows 8. It looks pretty interesting so far and VS2011 definitely helps making it easier to learn and create Metro Style Apps. One of the features available for developers is the ability to save user data so it can be retrieved the next time the app is run after being closed by the user or even launched from back suspended state. Here’s a little history on this whole ‘suspended’ state of a Metro Style app: Once the user say, ‘alt+tab...(read more)

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What happens at control invoke function?

- by user65909

A question about form controls invoke function. Control1 is created on thread1. If you want to update something in Control1 from thread2 you must do something like: delegate void SetTextCallback(string txt); void setText(string txt) { if (this.textBox1.InvokeRequired) { SetTextCallback d = new SetTextCallback(setText); this.Invoke(d, new object[] { txt }); } else { // this will run on thread1 even when called from thread2 this.textBox1.AppendText(msg); } }` What happens behind the scenes here? This invoke behaves different from a normal object invoke. When you want to call a function in an object on a specific thread, then that thread must be waiting on some queue of delegates, and execute the incoming delegates. Is it correct that the windows forms control invoke function is completely different from the standard object invoke function?

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Getting an OBB out of another OBB?

- by Milo

I'm working on collision resolution for my game. I just need a good way to get an object out of another object if it gets stuck. In this case a car. Here is a typical scenario. The red car is in the green object. How do I correctly get it out so the car can slide along the edge of the object as it should. I tried: if(buildings.size() > 0) { Entity e = buildings.get(0); Vector2D vel = new Vector2D(); vel.x = vehicle.getVelocity().x; vel.y = vehicle.getVelocity().y; vel.normalize(); while(vehicle.getRect().overlaps(e.getRect())) { vehicle.setCenter(vehicle.getCenterX() - vel.x * 0.1f, vehicle.getCenterY() - vel.y * 0.1f); } colided = true; } But that does not work too well. Is there some sort of vector I could calculate to use as the vector to move the car away from the object? Thanks

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What are good reasons to use explicit interface implementation for the sole purpose of hiding members?

- by Nathanus

During one of my studies into the intricacies of C#, I came across an interesting passage concerning explicit interface implementation. While this syntax is quite helpful when you need to resolve name clashes, you can use explicit interface implementation simply to hide more "advanced" members from the object level. The difference between allowing the use of object.method() or requiring the casting of ((Interface)object).method() seems like mean-spirited obfuscation to my inexperienced eyes. The text noted that this will hide the method from Intellisense at the object level, but why would you want to do that if it was not necessary to avoid name conflicts?

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How can light sensor be enabled for control brightness and keyboard back-light automatically?

- by Eng.amr19

I have A Sony VAIO laptop F-series () Nvidia and it has light sensor. When I was using Windows, this light sensor controlled the brightness and the keyboard backlight automatically due to the surroundings state. But when using Ubuntu 12.04, it only controls the backlight without automatically adjusting the brightness. How can I enable light sensor to automatically adjustment the LCD brightness without losing the keyboard backlight adjustment due to surrounding state?

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Better use on the name of variables

- by Cuartico

I have a method that looks like this: Public Function NormalizeStreetAddress(country As Namespace.Country, streetAddress As Namespace.StreetAddress) _ As Namespace.StreetAddress Dim _streetAddress As New Namespace.StreetAddress = streetAddress If My.Settings.Streeteable = True Then Dim _AddressCustom As New Namespace.AddressCustom _streetAddress = _AddressCustom.NormalizeStreetAddress(country, streetAddress) End If Return _streetAddress End Function I receive a streetAddress object, but inside the method I need to use another streetAddress object which I called _streetAddress — is that following the standard? A friend of mine told me that object names such as _yourNameObject are for global variables, but I can't find info about this and I want to make this method more readable.

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Best Creational Pattern for loggers in a multi-threaded system?

- by Dipan Mehta

This is a follow up question on my past questions : Concurrency pattern of logger in multithreaded application As suggested by others, I am putting this question separately. As the learning from the last question. In a multi-threaded environment, the logger should be made thread safe and probably asynchronous (where in messages are queued while a background thread does writing releasing the requesting object thread). The logger could be signleton or it can be a per-group logger which is a generalization of the above. Now, the question that arise is how does logger should be assigned to the object? There are two options I can think of: 1. Object requesting for the logger: Should each of the object call some global API such as get_logger()? Such an API returns "the" singleton or the group logger. However, I feel this involves assumption about the Application environment to implement the logger -which I think is some kind of coupling. If the same object needs to be used by other application - this new application also need to implement such a method. 2. Assign logger through some known API The other alternative approach is to create a kind of virtual class which is implemented by application based on App's own structure and assign the object sometime in the constructor. This is more generalized method. Unfortunately, when there are so many objects - and rather a tree of objects passing on the logger objects to each level is quite messy. My question is there a better way to do this? If you need to pick any one of the above, which approach is would you pick and why? Other questions remain open about how to configure them: How do objects' names or ID are assigned so that will be used for printing on the log messages (as the module names) How do these objects find the appropriate properties (such as log levels, and other such parameters) In the first approach, the central API needs to deal with all this varieties. In the second approach - there needs to be additional work. Hence, I want to understand from the real experience of people, as to how to write logger effectively in such an environment.

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Is `break` and `continue` bad programming practice?

- by Mikhail

My boss keeps mentioning nonchalantly that bad programmers use break and continue in loops. I use them all the time because they make sense; let me show you the inspiration: function verify(object) { if (object->value < 0) return false; if (object->value > object->max_value) return false; if (object->name == "") return false; ... } The point here is that first the function checks that the conditions are correct, then executes the actual functionality. IMO same applies with loops: while (primary_condition) { if (loop_count > 1000) break; if (time_exect > 3600) break; if (this->data == "undefined") continue; if (this->skip == true) continue; ... } I think this makes it easier to read & debug; but I also don't see a downside. Please comment.

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Strategies for managUse of types in Python

- by dave

I'm a long time programmer in C# but have been coding in Python for the past year. One of the big hurdles for me was the lack of type definitions for variables and parameters. Whereas I totally get the idea of duck typing, I do find it frustrating that I can't tell the type of a variable just by looking at it. This is an issue when you look at someone else's code where they've used ambiguous names for method parameters (see edit below). In a few cases, I've added asserts to ensure parameters comply with an expected type but this goes against the whole duck typing thing. On some methods, I'll document the expected type of parameters (eg: list of user objects), but even this seems to go against the idea of just using an object and let the runtime deal with exceptions. What strategies do you use to avoid typing problems in Python? Edit: Example of the parameter naming issues: If our code base we have a task object (ORM object) and a task_obj object (higher level object that embeds a task). Needless to say, many methods accept a parameter named 'task'. The method might expect a task or a task_obj or some other construct such as a dictionary of task properties - it is not clear. It is them up to be to look at how that parameter is used in order to work out what the method expects.

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Using PowerShell, in Active Direcotry, how would I change all the DNS A records that have a given IP to a new IP?

- by djsumdog

We've been moving data centers and I have a lot of old records that were not correctly but in DNS as CNAME records, but A records that have a direct IP (e.g. 192.168.100.n) and they're all moving to a new subnet (10.19.100.n). I just need to write a powershell script to change all those records. I found this site: http://www.indented.co.uk/index.php/2008/12/30/administering-microsoft-dns-in-powershell/ and from it I made this simple script: $dnsServer = "meldc2" $scope = New-Object Management.ManagementScope("\\$dnsServer\root\MicrosoftDNS") $path = New-Object Management.ManagementPath("MicrosoftDNS_Zone") $options = New-Object Management.ObjectGetOptions($Null,[System.TimeSpan]::MaxValue, $True) $ZoneClass= New-Object Management.ManagementClass($scope,$path,$options) $Zones = Get-WMIObject -Computer $dnsServer -Namespace "root\MicrosoftDNS" -Class "MicrosoftDNS_Zone" $Zones | Get-Member foreach($Z in $Zones) { $Z | Select-Object Name,DsIntegrated,ZoneType,Reverse,Data } but that only gets me a listing of root zones. I don't understand how to iterate over all the entries in each of the zones. Also, all the examples I've seen involve adding new zones, but there aren't any examples I can find on modifying existing A records.

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Passing Strings by Ref

- by SGWellens

Humbled yet again…DOH! No matter how much experience you acquire, no matter how smart you may be, no matter how hard you study, it is impossible to keep fully up to date on all the nuances of the technology we are exposed to. There will always be gaps in our knowledge: Little 'dead zones' of uncertainty. For me, this time, it was about passing string parameters to functions. I thought I knew this stuff cold. First, a little review... Value Types and Ref Integers and structs are value types (as opposed to reference types). When declared locally, their memory storage is on the stack; not on the heap. When passed to a function, the function gets a copy of the data and works on the copy. If a function needs to change a value type, you need to use the ref keyword. Here's an example: // ---- declaration ----------------- public struct MyStruct { public string StrTag; } // ---- functions ----------------------- void SetMyStruct(MyStruct myStruct) // pass by value { myStruct.StrTag = "BBB"; } void SetMyStruct(ref MyStruct myStruct) // pass by ref { myStruct.StrTag = "CCC"; } // ---- Usage ----------------------- protected void Button1_Click(object sender, EventArgs e) { MyStruct Data; Data.StrTag = "AAA"; SetMyStruct(Data); // Data.StrTag is still "AAA" SetMyStruct(ref Data); // Data.StrTag is now "CCC" } No surprises here. All value types like ints, floats, datetimes, enums, structs, etc. work the same way. And now on to... Class Types and Ref // ---- Declaration ----------------------------- public class MyClass { public string StrTag; } // ---- Functions ---------------------------- void SetMyClass(MyClass myClass) // pass by 'value' { myClass.StrTag = "BBB"; } void SetMyClass(ref MyClass myClass) // pass by ref { myClass.StrTag = "CCC"; } // ---- Usage --------------------------------------- protected void Button2_Click(object sender, EventArgs e) { MyClass Data = new MyClass(); Data.StrTag = "AAA"; SetMyClass(Data); // Data.StrTag is now "BBB" SetMyClass(ref Data); // Data.StrTag is now "CCC" } No surprises here either. Since Classes are reference types, you do not need the ref keyword to modify an object. What may seem a little strange is that with or without the ref keyword, the results are the same: The compiler knows what to do. So, why would you need to use the ref keyword when passing an object to a function? Because then you can change the reference itself…ie you can make it refer to a completely different object. Inside the function you can do: myClass = new MyClass() and the old object will be garbage collected and the new object will be returned to the caller. That ends the review. Now let's look at passing strings as parameters. The String Type and Ref Strings are reference types. So when you pass a String to a function, you do not need the ref keyword to change the string. Right? Wrong. Wrong, wrong, wrong. When I saw this, I was so surprised that I fell out of my chair. Getting up, I bumped my head on my desk (which really hurt). My bumping the desk caused a large speaker to fall off of a bookshelf and land squarely on my big toe. I was screaming in pain and hopping on one foot when I lost my balance and fell. I struck my head on the side of the desk (once again) and knocked myself out cold. When I woke up, I was in the hospital where due to a database error (thanks Oracle) the doctors had put casts on both my hands. I'm typing this ever so slowly with just my ton..tong ..tongu…tongue. But I digress. Okay, the only true part of that story is that I was a bit surprised. Here is what happens passing a String to a function. // ---- Functions ---------------------------- void SetMyString(String myString) // pass by 'value' { myString = "BBB"; } void SetMyString(ref String myString) // pass by ref { myString = "CCC"; } // ---- Usage --------------------------------- protected void Button3_Click(object sender, EventArgs e) { String MyString = "AAA"; SetMyString(MyString); // MyString is still "AAA" What!!!! SetMyString(ref MyString); // MyString is now "CCC" } What the heck. We should not have to use the ref keyword when passing a String because Strings are reference types. Why didn't the string change? What is going on? I spent hours unssuccessfully researching this anomaly until finally, I had a Eureka moment: This code: String MyString = "AAA"; Is semantically equivalent to this code (note this code doesn't actually compile): String MyString = new String(); MyString = "AAA"; Key Point: In the function, the copy of the reference is pointed to a new object and THAT object is modified. The original reference and what it points to is unchanged. You can simulate this behavior by modifying the class example code to look like this: void SetMyClass(MyClass myClass) // call by 'value' { //myClass.StrTag = "BBB"; myClass = new MyClass(); myClass.StrTag = "BBB"; } Now when you call the SetMyClass function without using ref, the parameter is unchanged...just like the string example. I hope someone finds this useful. Steve Wellens

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