Question

I’m building a custom control for Windows Phone 7+ that can do augmented reality image processing. The control works wonderfully in practice (when I run the app), but because I have the image processing running on a separate thread, it breaks when I try to open the page in Blend or the Visual Studio designer.

Here’s an example of the thread I’m trying to run (basically taken from http://msdn.microsoft.com/en-us/library/hh202982(v=vs.92).aspx) :

public override void OnApplyTemplate()
{
    // assigning template stuff, initializing my camera

    _myManualResetEvent = new ManualResetEvent(true);
    _myCameraProcessingThread = new System.Threading.Thread(ProcessingMethod);
    _myCameraProcessingThread.Start();
}

void ProcessingMethod()
{
    int[] myBuffer = new int[640 * 480];
    while(_someCondition)
    {
        _myManualResetEvent.WaitOne();
        _myCamera.GetPreviewBufferArgb32(myBuffer);
        // do my processing stuff
        _myManualResetEvent.Set();
    }
}

This breaks the ever-loving heck out of Blend. Would love to know why.

Answer 1

It looks like you are doing a lot of run-time stuff in the OnApplyTemplate method.

This will get called when Blend or Visual Studio instantiates the design view of your control.

You should either check to see if you are in design mode using the DesignMode:

if (!DesignMode)
{
    _myManualResetEvent = new ManualResetEvent(true);
    _myCameraProcessingThread = new System.Threading.Thread(ProcessingMethod);
    _myCameraProcessingThread.Start();
}

or move this code into a method/event handler that only gets called when the application actually runs.