System.NullReferenceException in Silverlight application designer in Visual Studio 2010

System.NullReferenceException in Silverlight application designer in Visual Studio 2010

This is my Environment:

1. Windows 7 64 bit
2. VisualStudio 2010 with SilverLight 4 developer runtime

Problem: After upgrading the SilverLight 5 client, I tried to create a SilverLight Application and then I have got the following wired error message on the design tab 

The text format of the error is:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

System.NullReferenceException Object reference not set to an instance of an object. at Microsoft.Windows.Design.Platform.SilverlightMetadataContext.SilverlightXamlExtensionImplementations.d__8.MoveNext() at MS.Internal.Design.Metadata.ReflectionProjectNode.BuildSubsumption() at MS.Internal.Design.Metadata.ReflectionProjectNode.SubsumingNamespace(Identifier identifier) at MS.Internal.Design.Markup.XmlElement.BuildScope(PrefixScope parentScope, IParseContext context) at MS.Internal.Design.Markup.XmlElement.ConvertToXaml(XamlElement parent, PrefixScope parentScope, IParseContext context, IMarkupSourceProvider provider) at MS.Internal.Design.DocumentModel.DocumentTrees.Markup.XamlSourceDocument.FullParse(Boolean convertToXamlWithErrors) at MS.Internal.Design.DocumentModel.DocumentTrees.Markup.XamlSourceDocument.get_RootItem() at Microsoft.Windows.Design.DocumentModel.Trees.ModifiableDocumentTree.get_ModifiableRootItem() at Microsoft.Windows.Design.DocumentModel.MarkupDocumentManagerBase.get_LoadState() at MS.Internal.Host.PersistenceSubsystem.Load() at MS.Internal.Host.Designer.Load() at MS.Internal.Designer.VSDesigner.Load() at MS.Internal.Designer.VSIsolatedDesigner.VSIsolatedView.Load() at MS.Internal.Designer.VSIsolatedDesigner.VSIsolatedDesignerFactory.Load(IsolatedView view) at MS.Internal.Host.Isolation.IsolatedDesigner.BootstrapProxy.LoadDesigner(IsolatedDesignerFactory factory, IsolatedView view) at MS.Internal.Host.Isolation.IsolatedDesigner.BootstrapProxy.LoadDesigner(IsolatedDesignerFactory factory, IsolatedView view) at MS.Internal.Host.Isolation.IsolatedDesigner.Load() at MS.Internal.Designer.DesignerPane.LoadDesignerView()

Solution: The problem is the conflict of SilverLight versions and I have found the solution in this thread.

Step 1: Uninstall the latest SilverLight client which is SilverLight  5, the 1st one in the below control panel screen shot

Step 2: Uninstall SilverLight 4 developer, the next 1 in the above image

Step 3: Download and Install Microsoft Silverlight 4 Tools for Visual Studio 2010 (Add-on and pre-requisite files for Visual Studio 2010 to develop Silverlight 4 and RIA Services applications)

Installing..!

Installation finished successfully.

Restart the VisualStudio 2010, wow.. it’s working! 

Happy Silverlighting..! Thanks R./

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GO to windows link

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other solution

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BackgroundWorker in c#

Creating a BackgroundWorker

We can create the BackgroundWorker at design-time by dragging onto a Form or at run-time using the BackgroundWorker class.  The following code is added when you drag a BackgroundWorker component onto a Form.

private System.ComponentModel.BackgroundWorker backgroundWorker1;

this.backgroundWorker1 = new System.ComponentModel.BackgroundWorker(); 

BackgroundWorker Properties

Here is a list of BackgroundWorker class properties.

CancellationPending - Indicates if an application has requested cancellation of a BackgroundWorker.

IsBusy - Indicates if a BackgroundWorker is running an asynchronous operation.

WorkerReportsProgress - Indicates of a BackgroundWorker can report progress updates.

WorkerSupportsCancellation - Indicates if a BackgroundWorker supports asynchronous cancellation.

Methods

BackgroundWorker has two methods, RunWorkerAsync and CancelAsync. The RunWorkerAsync starts the thread and the CancelAsync stops the thread.

Events

DoWork event is the starting point for a BackgroundWorker. This event is fired when the RunWorkerAsync method is called. In this event hander, we call our code that is being processed in the background where our application is still doing some other work.

this.backgroundWorker1.DoWork += newSystem.ComponentModel.DoWorkEventHandler(this.backgroundWorker1_DoWork);

The DoWork event handler looks like this where we need to call our time-consuming method.

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)

{

    BackgroundProcessLogicMethod();

}

ProgressChanged event occurs when ReportProgress is called.

RunWorkerCompleted event occurs when the background operation has completed.

Working Sample

Now we are going to create a sample application. The user interface looks like Figure 1 where a Form has two Button controls and a RichTextBox control. While BackgroundWorker will be doing some background work, user can still type in the RichTextBox.

Figure 1

Start button click starts the processing BackgroundWorker and Stop button click stops the processing. While BackgroundWorker is doing work in the background, you may still type anything in the RichTextBox control.

The Start and Stop button click event handlers looks like this.

private void StartButton_Click(object sender, EventArgs e)

{

    // Start BackgroundWorker

    backgroundWorker1.RunWorkerAsync(2000);

}

private void StopButton_Click(object sender, EventArgs e)

{

    // Cancel BackgroundWorker

    if (!backgroundWorker1.IsBusy)

        backgroundWorker1.CancelAsync();

}

And here is the code for the DoWork event, background worker method and WorkerCompleted event.

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)

{

    BackgroundWorker helperBW = sender as BackgroundWorker;

    int arg = (int)e.Argument;

    e.Result = BackgroundProcessLogicMethod(helperBW, arg);

    if (helperBW.CancellationPending)

    {

        e.Cancel = true;

    }

}

// Put all of background logic that is taking too much time

private int BackgroundProcessLogicMethod(BackgroundWorker bw, int a)

{

    int result = 0;

    Thread.Sleep(20000);

    MessageBox.Show("I was doing some work in the background.");

    return result;

}

private void backgroundWorker1_RunWorkerCompleted(object sender,

    RunWorkerCompletedEventArgs e)

{

    if (e.Cancelled) MessageBox.Show("Operation was canceled");

    else if (e.Error != null) MessageBox.Show(e.Error.Message);

    else MessageBox.Show(e.Result.ToString());

}