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  • Combobox seems to reload itself

    - by developer
    Hi, I have a combo box drop down for fonts in one of the apps. Now when I click on the dropdown to see the available list of fonts, I see a flickering effect. It seems as if the combo box keeps on reloading itself or getting refreshed. Is it because it covers some of the other UI elements like textboxes when I click to expand the list, or is it some kind of known bug with WPF? Is there a workaround for this?

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  • jquery not select?

    - by acidzombie24
    i have a click event for $('#blah div'). div has text inside of it (not inside a div, span, p, etc) and has a textarea in it. The textarea is triggering the event as well, how do i make it only trigger when i click the text and ignore the textarea?

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  • How to automate the java Applet(tree view) from my .NET application.

    - by rajeev-vj
    Hi I have a java applet (tree view) on Internet Explorer. when i Click on this applet (+) it collapes, as the information is based on this plus sign. I need to automate this java applet to click automatically from my C#.NET winforms application but am not able to get the details of the java applet. How to get the details of the java applet from browser and how to automate the java applet? Thanks

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  • populate href of link for next and previous

    - by sea_1987
    Hi There, I am struggling alot with some PHP I am needing to implement a next and previous link, basically I have a search function on my site, that returns multiple results and click on a result navigates to that results page, I want to then be able to click next on that page, and be taken to the next result in the sequence that was returned by the users original search? Is this possible, and how? I have no clue.

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  • Download a file+

    - by Martin
    Hi, First PHP project and I'm stuck! I wish to allow users to click a button or a link and download a file. However, my PHP must first perform some tasks, choose the right file, record the download event in a db etc. This I can do, but how do I then send the file as a response to the user's click? Thanks for any help.

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  • jquery add either of two fields to form

    - by user2891182
    I have worked out how to add a field to a form through JQuery but cannot figure out how to have two add field buttons so I can add one or the other fields? Could someone lead me in the right direction? <html> <head> <title>jQuery add / remove textbox example</title> <script type="text/javascript" src="jquery-1.3.2.min.js"></script> <style type="text/css"> div{ padding:8px; } </style> </head> <body> <h1>jQuery add / remove textbox example</h1> <script type="text/javascript"> $(document).ready(function(){ var counter = 2; $("#addButton").click(function () { if(counter>10){ alert("Only 10 textboxes allow"); return false; } var newTextBoxDiv = $(document.createElement('div')) .attr("id", 'TextBoxDiv' + counter); newTextBoxDiv.after().html('<label>Textbox #'+ counter + ' : </label>' + '<input type="text" name="textbox' + counter + '" id="textbox' + counter + '" value="" >'); newTextBoxDiv.appendTo("#TextBoxesGroup"); counter++; }); $("#removeButton").click(function () { if(counter==1){ alert("No more textbox to remove"); return false; } counter--; $("#TextBoxDiv" + counter).remove(); }); $("#getButtonValue").click(function () { var msg = ''; for(i=1; i<counter; i++){ msg += "\n Textbox #" + i + " : " + $('#textbox' + i).val(); } alert(msg); }); }); </script> </head><body> <div id='TextBoxesGroup'> <div id="TextBoxDiv1"> <label>Textbox #1 : </label><input type='textbox' id='textbox1' > </div> </div> --I am trying to have a use click on either of these two buttons and have the appropriate field added next.-- <input type='button' value='Add field #01' id='addButton'> <input type='button' value='Add field #02' id='addButton'> <input type='button' value='Remove Last Field' id='removeButton'> </body> </html>

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  • Saving an Object for use later

    - by Eclipsed4utoo
    As part of my widget, I use an instance of the Camera object. This is what I want to do. The user will click on my widget, I get an instance of the Camera(if it's not already stored), use it, then store it. If they click the widget again, I want to use that same instance that I used previously. Is this possible?

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  • Display DropDown options on Focus

    - by davidylam
    I have a simple html dropdown, I wants to use jQuery if possible to display all the options if this control has the focus(as if the user click on the dropdown). I have tried jQuery trigger(), click(), to avail. <select id="single"> <option>Single</option> <option>Single2</option> </select>

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  • Create a custom button

    - by Beppi Menozzi
    Sorry if this is too basic. I created a new class that extends Button: public class MyButton extends Button { private Context ctx; public MyButton(Context context) { super(context); ctx = context; } private void click() { // DO WHAT I NEED (FOR EXAMPLE CHANGE BACKGROUND) } } How can make it possible that, when I setOnClickListener() from another class where I instantiated this object, the click() method is called automatically? Thanks.

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  • explorer.exe opens slowly [closed]

    - by d9k
    explorer.exe opens veeeery slow when I press [Win+R] key or type "explorer ." in command prompt etc. But it opens with normal speed when I just click on the shortcut to any folder. When I click on the URL in IM like ICQ, already openned browser (firefox) takes too long to process link too. I have this problem for some months and I'm very tired of this. OS: WinXP SP3.

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  • Disabling CheckBoxes

    - by bbesase
    If I have 4 different CheckBoxes and when the user selects one of them I want the other 3 to become disabled so you can't click on a checkbox while another one is already checked how would I go about doing this? I have this, but it doesnt work right now and I thought it would: If NoDelayCheckMarkBox.Checked = True Then timeBetweenIterationDelay = 0 SecondDelayCheckMarkBox.Enabled = False HalfSecondDelayCheckMarkBox.Enabled = False FiftyMSDelayCheckMarkBox.Enabled = False I can still click as many check boxes as I want too. Thank you for any help.

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  • Parallelism in .NET – Part 10, Cancellation in PLINQ and the Parallel class

    - by Reed
    Many routines are parallelized because they are long running processes.  When writing an algorithm that will run for a long period of time, its typically a good practice to allow that routine to be cancelled.  I previously discussed terminating a parallel loop from within, but have not demonstrated how a routine can be cancelled from the caller’s perspective.  Cancellation in PLINQ and the Task Parallel Library is handled through a new, unified cooperative cancellation model introduced with .NET 4.0. Cancellation in .NET 4 is based around a new, lightweight struct called CancellationToken.  A CancellationToken is a small, thread-safe value type which is generated via a CancellationTokenSource.  There are many goals which led to this design.  For our purposes, we will focus on a couple of specific design decisions: Cancellation is cooperative.  A calling method can request a cancellation, but it’s up to the processing routine to terminate – it is not forced. Cancellation is consistent.  A single method call requests a cancellation on every copied CancellationToken in the routine. Let’s begin by looking at how we can cancel a PLINQ query.  Supposed we wanted to provide the option to cancel our query from Part 6: double min = collection .AsParallel() .Min(item => item.PerformComputation()); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } We would rewrite this to allow for cancellation by adding a call to ParallelEnumerable.WithCancellation as follows: var cts = new CancellationTokenSource(); // Pass cts here to a routine that could, // in parallel, request a cancellation try { double min = collection .AsParallel() .WithCancellation(cts.Token) .Min(item => item.PerformComputation()); } catch (OperationCanceledException e) { // Query was cancelled before it finished } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Here, if the user calls cts.Cancel() before the PLINQ query completes, the query will stop processing, and an OperationCanceledException will be raised.  Be aware, however, that cancellation will not be instantaneous.  When cts.Cancel() is called, the query will only stop after the current item.PerformComputation() elements all finish processing.  cts.Cancel() will prevent PLINQ from scheduling a new task for a new element, but will not stop items which are currently being processed.  This goes back to the first goal I mentioned – Cancellation is cooperative.  Here, we’re requesting the cancellation, but it’s up to PLINQ to terminate. If we wanted to allow cancellation to occur within our routine, we would need to change our routine to accept a CancellationToken, and modify it to handle this specific case: public void PerformComputation(CancellationToken token) { for (int i=0; i<this.iterations; ++i) { // Add a check to see if we've been canceled // If a cancel was requested, we'll throw here token.ThrowIfCancellationRequested(); // Do our processing now this.RunIteration(i); } } With this overload of PerformComputation, each internal iteration checks to see if a cancellation request was made, and will throw an OperationCanceledException at that point, instead of waiting until the method returns.  This is good, since it allows us, as developers, to plan for cancellation, and terminate our routine in a clean, safe state. This is handled by changing our PLINQ query to: try { double min = collection .AsParallel() .WithCancellation(cts.Token) .Min(item => item.PerformComputation(cts.Token)); } catch (OperationCanceledException e) { // Query was cancelled before it finished } PLINQ is very good about handling this exception, as well.  There is a very good chance that multiple items will raise this exception, since the entire purpose of PLINQ is to have multiple items be processed concurrently.  PLINQ will take all of the OperationCanceledException instances raised within these methods, and merge them into a single OperationCanceledException in the call stack.  This is done internally because we added the call to ParallelEnumerable.WithCancellation. If, however, a different exception is raised by any of the elements, the OperationCanceledException as well as the other Exception will be merged into a single AggregateException. The Task Parallel Library uses the same cancellation model, as well.  Here, we supply our CancellationToken as part of the configuration.  The ParallelOptions class contains a property for the CancellationToken.  This allows us to cancel a Parallel.For or Parallel.ForEach routine in a very similar manner to our PLINQ query.  As an example, we could rewrite our Parallel.ForEach loop from Part 2 to support cancellation by changing it to: try { var cts = new CancellationTokenSource(); var options = new ParallelOptions() { CancellationToken = cts.Token }; Parallel.ForEach(customers, options, customer => { // Run some process that takes some time... DateTime lastContact = theStore.GetLastContact(customer); TimeSpan timeSinceContact = DateTime.Now - lastContact; // Check for cancellation here options.CancellationToken.ThrowIfCancellationRequested(); // If it's been more than two weeks, send an email, and update... if (timeSinceContact.Days > 14) { theStore.EmailCustomer(customer); customer.LastEmailContact = DateTime.Now; } }); } catch (OperationCanceledException e) { // The loop was cancelled } Notice that here we use the same approach taken in PLINQ.  The Task Parallel Library will automatically handle our cancellation in the same manner as PLINQ, providing a clean, unified model for cancellation of any parallel routine.  The TPL performs the same aggregation of the cancellation exceptions as PLINQ, as well, which is why a single exception handler for OperationCanceledException will cleanly handle this scenario.  This works because we’re using the same CancellationToken provided in the ParallelOptions.  If a different exception was thrown by one thread, or a CancellationToken from a different CancellationTokenSource was used to raise our exception, we would instead receive all of our individual exceptions merged into one AggregateException.

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  • Qml and QfileSystemModel interaction problem

    - by user136432
    I'm having some problem in realizing an interaction between QML and C++ to obtain a very basic file browser that is shown within a ListView. I tried to use as model for my data the QT class QFileSystemModel, but it did't work as I expected, probably I didn't fully understand the QT class documentation about the use of this model or the example I found on the internet. Here is the code that I am using: File main.cpp #include <QModelIndex> #include <QFileSystemModel> #include <QQmlContext> #include <QApplication> #include "qtquick2applicationviewer.h" int main(int argc, char *argv[]) { QApplication app(argc, argv); QFileSystemModel* model = new QFileSystemModel; model->setRootPath("C:/"); model->setFilter(QDir::Files | QDir::AllDirs); QtQuick2ApplicationViewer viewer; // Make QFileSystemModel* available for QML use. viewer.rootContext()->setContextProperty("myFileModel", model); viewer.setMainQmlFile(QStringLiteral("qml/ProvaQML/main.qml")); viewer.showExpanded(); return app.exec(); } File main.qml Rectangle { id: main width: 800 height: 600 ListView { id: view property string root_path: "C:/Users" x: 40 y: 20 width: parent.width - (2*x) height: parent.height - (2*y) VisualDataModel { id: myVisualModel model: myFileModel // Get the model QFileSystemModel exposed from C++ delegate { Rectangle { width: 210; height: 20; radius: 5; border.width: 2; border.color: "orange"; color: "yellow"; Text { text: fileName; x: parent.x + 10; } MouseArea { anchors.fill: parent onDoubleClicked: { myVisualModel.rootIndex = myVisualModel.modelIndex(index) } } } } } highlight: Rectangle { color: "lightsteelblue"; radius: 5 } focus: true } } The first problem with this code is that first elements that I can see within my list are my PC logical drives even if I set a specific path. Then when I first double click on drive "C:\" it shows the list of files and directories on that path, but when I double click on a directory a second time the screen flickers for one moment and then it shows again the PC logical drives. Can anyone tell me how should I use the QFileSystemModel class with a ListView QML object? Thanks in advance! Carlo

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  • SEO - Delimiter character for page title

    - by cept0
    I have noticed a few oddities recently with the titles of web pages in SERPs. However, it seems there are several main conventions: Contact Page - Joe Schmoe's Awesome Site // &#045; Hyphen Contact Page — Joe Schmoe's Awesome Site // &mdash; Em dash Contact Page | Joe Schmoe's Awesome Site // &#x007C; Vertical bar Contact Page « Joe Schmoe's Awesome Site // &laquo; Left double angle quotes Is there any reason to use one over the other?

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  • Error occurred in deployment step ‘Add Solution’: Value does not fall within the expected range.

    - by ybbest
    I got this error when I deploy a new content type into SharePoint2010.This error message is not very helpful after a few hours of hard work, I find out there is a dash(-) in my contentID.It happen when I generate GUID using visual studio tool and copy it to the ID and forgot to delete the dash. After correct this, I press deploy again, it works like charm. If you got this error double-check your contentID. If you are not quite sure what is a Valid contentTypeID, check the MSDN documentation here.

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  • Scanner Review: HP Scanjet Professional 1000

    Your notebook computer's newest companion: a $249 ultraportable scanner that takes next to no briefcase space to turn double-sided documents, images, and business cards into PDFs, e-mails, and Outlook entries. We put the peripatetic peripheral to the test.

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  • Scanner Review: HP Scanjet Professional 1000

    Your notebook computer's newest companion: a $249 ultraportable scanner that takes next to no briefcase space to turn double-sided documents, images, and business cards into PDFs, e-mails, and Outlook entries. We put the peripatetic peripheral to the test.

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  • C#/.NET Little Wonders: The ConcurrentDictionary

    - by James Michael Hare
    Once again we consider some of the lesser known classes and keywords of C#.  In this series of posts, we will discuss how the concurrent collections have been developed to help alleviate these multi-threading concerns.  Last week’s post began with a general introduction and discussed the ConcurrentStack<T> and ConcurrentQueue<T>.  Today's post discusses the ConcurrentDictionary<T> (originally I had intended to discuss ConcurrentBag this week as well, but ConcurrentDictionary had enough information to create a very full post on its own!).  Finally next week, we shall close with a discussion of the ConcurrentBag<T> and BlockingCollection<T>. For more of the "Little Wonders" posts, see the index here. Recap As you'll recall from the previous post, the original collections were object-based containers that accomplished synchronization through a Synchronized member.  While these were convenient because you didn't have to worry about writing your own synchronization logic, they were a bit too finely grained and if you needed to perform multiple operations under one lock, the automatic synchronization didn't buy much. With the advent of .NET 2.0, the original collections were succeeded by the generic collections which are fully type-safe, but eschew automatic synchronization.  This cuts both ways in that you have a lot more control as a developer over when and how fine-grained you want to synchronize, but on the other hand if you just want simple synchronization it creates more work. With .NET 4.0, we get the best of both worlds in generic collections.  A new breed of collections was born called the concurrent collections in the System.Collections.Concurrent namespace.  These amazing collections are fine-tuned to have best overall performance for situations requiring concurrent access.  They are not meant to replace the generic collections, but to simply be an alternative to creating your own locking mechanisms. Among those concurrent collections were the ConcurrentStack<T> and ConcurrentQueue<T> which provide classic LIFO and FIFO collections with a concurrent twist.  As we saw, some of the traditional methods that required calls to be made in a certain order (like checking for not IsEmpty before calling Pop()) were replaced in favor of an umbrella operation that combined both under one lock (like TryPop()). Now, let's take a look at the next in our series of concurrent collections!For some excellent information on the performance of the concurrent collections and how they perform compared to a traditional brute-force locking strategy, see this wonderful whitepaper by the Microsoft Parallel Computing Platform team here. ConcurrentDictionary – the fully thread-safe dictionary The ConcurrentDictionary<TKey,TValue> is the thread-safe counterpart to the generic Dictionary<TKey, TValue> collection.  Obviously, both are designed for quick – O(1) – lookups of data based on a key.  If you think of algorithms where you need lightning fast lookups of data and don’t care whether the data is maintained in any particular ordering or not, the unsorted dictionaries are generally the best way to go. Note: as a side note, there are sorted implementations of IDictionary, namely SortedDictionary and SortedList which are stored as an ordered tree and a ordered list respectively.  While these are not as fast as the non-sorted dictionaries – they are O(log2 n) – they are a great combination of both speed and ordering -- and still greatly outperform a linear search. Now, once again keep in mind that if all you need to do is load a collection once and then allow multi-threaded reading you do not need any locking.  Examples of this tend to be situations where you load a lookup or translation table once at program start, then keep it in memory for read-only reference.  In such cases locking is completely non-productive. However, most of the time when we need a concurrent dictionary we are interleaving both reads and updates.  This is where the ConcurrentDictionary really shines!  It achieves its thread-safety with no common lock to improve efficiency.  It actually uses a series of locks to provide concurrent updates, and has lockless reads!  This means that the ConcurrentDictionary gets even more efficient the higher the ratio of reads-to-writes you have. ConcurrentDictionary and Dictionary differences For the most part, the ConcurrentDictionary<TKey,TValue> behaves like it’s Dictionary<TKey,TValue> counterpart with a few differences.  Some notable examples of which are: Add() does not exist in the concurrent dictionary. This means you must use TryAdd(), AddOrUpdate(), or GetOrAdd().  It also means that you can’t use a collection initializer with the concurrent dictionary. TryAdd() replaced Add() to attempt atomic, safe adds. Because Add() only succeeds if the item doesn’t already exist, we need an atomic operation to check if the item exists, and if not add it while still under an atomic lock. TryUpdate() was added to attempt atomic, safe updates. If we want to update an item, we must make sure it exists first and that the original value is what we expected it to be.  If all these are true, we can update the item under one atomic step. TryRemove() was added to attempt atomic, safe removes. To safely attempt to remove a value we need to see if the key exists first, this checks for existence and removes under an atomic lock. AddOrUpdate() was added to attempt an thread-safe “upsert”. There are many times where you want to insert into a dictionary if the key doesn’t exist, or update the value if it does.  This allows you to make a thread-safe add-or-update. GetOrAdd() was added to attempt an thread-safe query/insert. Sometimes, you want to query for whether an item exists in the cache, and if it doesn’t insert a starting value for it.  This allows you to get the value if it exists and insert if not. Count, Keys, Values properties take a snapshot of the dictionary. Accessing these properties may interfere with add and update performance and should be used with caution. ToArray() returns a static snapshot of the dictionary. That is, the dictionary is locked, and then copied to an array as a O(n) operation.  GetEnumerator() is thread-safe and efficient, but allows dirty reads. Because reads require no locking, you can safely iterate over the contents of the dictionary.  The only downside is that, depending on timing, you may get dirty reads. Dirty reads during iteration The last point on GetEnumerator() bears some explanation.  Picture a scenario in which you call GetEnumerator() (or iterate using a foreach, etc.) and then, during that iteration the dictionary gets updated.  This may not sound like a big deal, but it can lead to inconsistent results if used incorrectly.  The problem is that items you already iterated over that are updated a split second after don’t show the update, but items that you iterate over that were updated a split second before do show the update.  Thus you may get a combination of items that are “stale” because you iterated before the update, and “fresh” because they were updated after GetEnumerator() but before the iteration reached them. Let’s illustrate with an example, let’s say you load up a concurrent dictionary like this: 1: // load up a dictionary. 2: var dictionary = new ConcurrentDictionary<string, int>(); 3:  4: dictionary["A"] = 1; 5: dictionary["B"] = 2; 6: dictionary["C"] = 3; 7: dictionary["D"] = 4; 8: dictionary["E"] = 5; 9: dictionary["F"] = 6; Then you have one task (using the wonderful TPL!) to iterate using dirty reads: 1: // attempt iteration in a separate thread 2: var iterationTask = new Task(() => 3: { 4: // iterates using a dirty read 5: foreach (var pair in dictionary) 6: { 7: Console.WriteLine(pair.Key + ":" + pair.Value); 8: } 9: }); And one task to attempt updates in a separate thread (probably): 1: // attempt updates in a separate thread 2: var updateTask = new Task(() => 3: { 4: // iterates, and updates the value by one 5: foreach (var pair in dictionary) 6: { 7: dictionary[pair.Key] = pair.Value + 1; 8: } 9: }); Now that we’ve done this, we can fire up both tasks and wait for them to complete: 1: // start both tasks 2: updateTask.Start(); 3: iterationTask.Start(); 4:  5: // wait for both to complete. 6: Task.WaitAll(updateTask, iterationTask); Now, if I you didn’t know about the dirty reads, you may have expected to see the iteration before the updates (such as A:1, B:2, C:3, D:4, E:5, F:6).  However, because the reads are dirty, we will quite possibly get a combination of some updated, some original.  My own run netted this result: 1: F:6 2: E:6 3: D:5 4: C:4 5: B:3 6: A:2 Note that, of course, iteration is not in order because ConcurrentDictionary, like Dictionary, is unordered.  Also note that both E and F show the value 6.  This is because the output task reached F before the update, but the updates for the rest of the items occurred before their output (probably because console output is very slow, comparatively). If we want to always guarantee that we will get a consistent snapshot to iterate over (that is, at the point we ask for it we see precisely what is in the dictionary and no subsequent updates during iteration), we should iterate over a call to ToArray() instead: 1: // attempt iteration in a separate thread 2: var iterationTask = new Task(() => 3: { 4: // iterates using a dirty read 5: foreach (var pair in dictionary.ToArray()) 6: { 7: Console.WriteLine(pair.Key + ":" + pair.Value); 8: } 9: }); The atomic Try…() methods As you can imagine TryAdd() and TryRemove() have few surprises.  Both first check the existence of the item to determine if it can be added or removed based on whether or not the key currently exists in the dictionary: 1: // try add attempts an add and returns false if it already exists 2: if (dictionary.TryAdd("G", 7)) 3: Console.WriteLine("G did not exist, now inserted with 7"); 4: else 5: Console.WriteLine("G already existed, insert failed."); TryRemove() also has the virtue of returning the value portion of the removed entry matching the given key: 1: // attempt to remove the value, if it exists it is removed and the original is returned 2: int removedValue; 3: if (dictionary.TryRemove("C", out removedValue)) 4: Console.WriteLine("Removed C and its value was " + removedValue); 5: else 6: Console.WriteLine("C did not exist, remove failed."); Now TryUpdate() is an interesting creature.  You might think from it’s name that TryUpdate() first checks for an item’s existence, and then updates if the item exists, otherwise it returns false.  Well, note quite... It turns out when you call TryUpdate() on a concurrent dictionary, you pass it not only the new value you want it to have, but also the value you expected it to have before the update.  If the item exists in the dictionary, and it has the value you expected, it will update it to the new value atomically and return true.  If the item is not in the dictionary or does not have the value you expected, it is not modified and false is returned. 1: // attempt to update the value, if it exists and if it has the expected original value 2: if (dictionary.TryUpdate("G", 42, 7)) 3: Console.WriteLine("G existed and was 7, now it's 42."); 4: else 5: Console.WriteLine("G either didn't exist, or wasn't 7."); The composite Add methods The ConcurrentDictionary also has composite add methods that can be used to perform updates and gets, with an add if the item is not existing at the time of the update or get. The first of these, AddOrUpdate(), allows you to add a new item to the dictionary if it doesn’t exist, or update the existing item if it does.  For example, let’s say you are creating a dictionary of counts of stock ticker symbols you’ve subscribed to from a market data feed: 1: public sealed class SubscriptionManager 2: { 3: private readonly ConcurrentDictionary<string, int> _subscriptions = new ConcurrentDictionary<string, int>(); 4:  5: // adds a new subscription, or increments the count of the existing one. 6: public void AddSubscription(string tickerKey) 7: { 8: // add a new subscription with count of 1, or update existing count by 1 if exists 9: var resultCount = _subscriptions.AddOrUpdate(tickerKey, 1, (symbol, count) => count + 1); 10:  11: // now check the result to see if we just incremented the count, or inserted first count 12: if (resultCount == 1) 13: { 14: // subscribe to symbol... 15: } 16: } 17: } Notice the update value factory Func delegate.  If the key does not exist in the dictionary, the add value is used (in this case 1 representing the first subscription for this symbol), but if the key already exists, it passes the key and current value to the update delegate which computes the new value to be stored in the dictionary.  The return result of this operation is the value used (in our case: 1 if added, existing value + 1 if updated). Likewise, the GetOrAdd() allows you to attempt to retrieve a value from the dictionary, and if the value does not currently exist in the dictionary it will insert a value.  This can be handy in cases where perhaps you wish to cache data, and thus you would query the cache to see if the item exists, and if it doesn’t you would put the item into the cache for the first time: 1: public sealed class PriceCache 2: { 3: private readonly ConcurrentDictionary<string, double> _cache = new ConcurrentDictionary<string, double>(); 4:  5: // adds a new subscription, or increments the count of the existing one. 6: public double QueryPrice(string tickerKey) 7: { 8: // check for the price in the cache, if it doesn't exist it will call the delegate to create value. 9: return _cache.GetOrAdd(tickerKey, symbol => GetCurrentPrice(symbol)); 10: } 11:  12: private double GetCurrentPrice(string tickerKey) 13: { 14: // do code to calculate actual true price. 15: } 16: } There are other variations of these two methods which vary whether a value is provided or a factory delegate, but otherwise they work much the same. Oddities with the composite Add methods The AddOrUpdate() and GetOrAdd() methods are totally thread-safe, on this you may rely, but they are not atomic.  It is important to note that the methods that use delegates execute those delegates outside of the lock.  This was done intentionally so that a user delegate (of which the ConcurrentDictionary has no control of course) does not take too long and lock out other threads. This is not necessarily an issue, per se, but it is something you must consider in your design.  The main thing to consider is that your delegate may get called to generate an item, but that item may not be the one returned!  Consider this scenario: A calls GetOrAdd and sees that the key does not currently exist, so it calls the delegate.  Now thread B also calls GetOrAdd and also sees that the key does not currently exist, and for whatever reason in this race condition it’s delegate completes first and it adds its new value to the dictionary.  Now A is done and goes to get the lock, and now sees that the item now exists.  In this case even though it called the delegate to create the item, it will pitch it because an item arrived between the time it attempted to create one and it attempted to add it. Let’s illustrate, assume this totally contrived example program which has a dictionary of char to int.  And in this dictionary we want to store a char and it’s ordinal (that is, A = 1, B = 2, etc).  So for our value generator, we will simply increment the previous value in a thread-safe way (perhaps using Interlocked): 1: public static class Program 2: { 3: private static int _nextNumber = 0; 4:  5: // the holder of the char to ordinal 6: private static ConcurrentDictionary<char, int> _dictionary 7: = new ConcurrentDictionary<char, int>(); 8:  9: // get the next id value 10: public static int NextId 11: { 12: get { return Interlocked.Increment(ref _nextNumber); } 13: } Then, we add a method that will perform our insert: 1: public static void Inserter() 2: { 3: for (int i = 0; i < 26; i++) 4: { 5: _dictionary.GetOrAdd((char)('A' + i), key => NextId); 6: } 7: } Finally, we run our test by starting two tasks to do this work and get the results… 1: public static void Main() 2: { 3: // 3 tasks attempting to get/insert 4: var tasks = new List<Task> 5: { 6: new Task(Inserter), 7: new Task(Inserter) 8: }; 9:  10: tasks.ForEach(t => t.Start()); 11: Task.WaitAll(tasks.ToArray()); 12:  13: foreach (var pair in _dictionary.OrderBy(p => p.Key)) 14: { 15: Console.WriteLine(pair.Key + ":" + pair.Value); 16: } 17: } If you run this with only one task, you get the expected A:1, B:2, ..., Z:26.  But running this in parallel you will get something a bit more complex.  My run netted these results: 1: A:1 2: B:3 3: C:4 4: D:5 5: E:6 6: F:7 7: G:8 8: H:9 9: I:10 10: J:11 11: K:12 12: L:13 13: M:14 14: N:15 15: O:16 16: P:17 17: Q:18 18: R:19 19: S:20 20: T:21 21: U:22 22: V:23 23: W:24 24: X:25 25: Y:26 26: Z:27 Notice that B is 3?  This is most likely because both threads attempted to call GetOrAdd() at roughly the same time and both saw that B did not exist, thus they both called the generator and one thread got back 2 and the other got back 3.  However, only one of those threads can get the lock at a time for the actual insert, and thus the one that generated the 3 won and the 3 was inserted and the 2 got discarded.  This is why on these methods your factory delegates should be careful not to have any logic that would be unsafe if the value they generate will be pitched in favor of another item generated at roughly the same time.  As such, it is probably a good idea to keep those generators as stateless as possible. Summary The ConcurrentDictionary is a very efficient and thread-safe version of the Dictionary generic collection.  It has all the benefits of type-safety that it’s generic collection counterpart does, and in addition is extremely efficient especially when there are more reads than writes concurrently. Tweet Technorati Tags: C#, .NET, Concurrent Collections, Collections, Little Wonders, Black Rabbit Coder,James Michael Hare

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  • JavaFX, Google Maps, and NetBeans Platform

    - by Geertjan
    Thanks to a great new article by Rob Terpilowski, and other work and research he describes in that article, it's now trivial to introduce a map component to a NetBeans Platform application. Making use of the GMapsFX library, as described in Rob's article, which provides a JavaFX API for Google Maps, you can very quickly knock this application together. Click to enlarge the image. Here's all the code (from Rob's article): @TopComponent.Description( preferredID = "MapTopComponent", persistenceType = TopComponent.PERSISTENCE_ALWAYS ) @TopComponent.Registration(mode = "editor", openAtStartup = true) @ActionID(category = "Window", id = "org.map.MapTopComponent") @ActionReference(path = "Menu/Window" /*, position = 333 */) @TopComponent.OpenActionRegistration( displayName = "#CTL_MapWindowAction", preferredID = "MapTopComponent" ) @NbBundle.Messages({ "CTL_MapWindowAction=Map", "CTL_MapTopComponent=Map Window", "HINT_MapTopComponent=This is a Map window" }) public class MapWindow extends TopComponent implements MapComponentInitializedListener { protected GoogleMapView mapComponent; protected GoogleMap map; private static final double latitude = 52.3667; private static final double longitude = 4.9000; public MapWindow() { setName(Bundle.CTL_MapTopComponent()); setToolTipText(Bundle.HINT_MapTopComponent()); setLayout(new BorderLayout()); JFXPanel panel = new JFXPanel(); Platform.setImplicitExit(false); Platform.runLater(() -> { mapComponent = new GoogleMapView(); mapComponent.addMapInializedListener(this); BorderPane root = new BorderPane(mapComponent); Scene scene = new Scene(root); panel.setScene(scene); }); add(panel, BorderLayout.CENTER); } @Override public void mapInitialized() { //Once the map has been loaded by the Webview, initialize the map details. LatLong center = new LatLong(latitude, longitude); MapOptions options = new MapOptions(); options.center(center) .mapMarker(true) .zoom(9) .overviewMapControl(false) .panControl(false) .rotateControl(false) .scaleControl(false) .streetViewControl(false) .zoomControl(false) .mapType(MapTypeIdEnum.ROADMAP); map = mapComponent.createMap(options); //Add a couple of markers to the map. MarkerOptions markerOptions = new MarkerOptions(); LatLong markerLatLong = new LatLong(latitude, longitude); markerOptions.position(markerLatLong) .title("My new Marker") .animation(Animation.DROP) .visible(true); Marker myMarker = new Marker(markerOptions); MarkerOptions markerOptions2 = new MarkerOptions(); LatLong markerLatLong2 = new LatLong(latitude, longitude); markerOptions2.position(markerLatLong2) .title("My new Marker") .visible(true); Marker myMarker2 = new Marker(markerOptions2); map.addMarker(myMarker); map.addMarker(myMarker2); //Add an info window to the Map. InfoWindowOptions infoOptions = new InfoWindowOptions(); infoOptions.content("<h2>Center of the Universe</h2>") .position(center); InfoWindow window = new InfoWindow(infoOptions); window.open(map, myMarker); } } Awesome work Rob, will be useful for many developers out there.

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