Silverlight Application Almost Freezes When Loading Images Using WebClient (ChildWindow Used as ProgressBar)

Question

I have this weird issue.

The code I have on my main thread:

WebClient client = new WebClient();
client.OpenReadCompleted += new OpenReadCompletedEventHandler((ss, ee) =>
{
    Dispatcher.BeginInvoke(() =>
    {
        try
        {
            BitmapImage bi = new BitmapImage();
            bi.SetSource(ee.Result);
            WriteableBitmap wb = new WriteableBitmap(bi);
            _okAction.Invoke(linkTexBox.Text, wb);

            theProgressBarDialog.Close();
        }
        catch (Exception)
        {
            theProgressBarDialog.Close();

            string msg = "Cannot fetch the image.  Please make sure the image URL is correct";
            MessageBox.Show(msg);
        }
    });
});
client.OpenReadAsync(new Uri("Image URL without cross domain problem"));
theProgressBarDialog.Show();

The image is loaded successfully, and got rendered on my canvas.

The weird behavior is sometimes, my whole Silverlight application seems freezing, the app does not respond to any user action EXCEPT the right-click, which pops up the default Silverlight context menu.

The buttons are disabled forcefully.

When debugging, no exception is thrown.

EDIT: If I set client.AllowReadStreamBuffering = false, I will get exception:

{System.NotSupportedException: Read is not supported on the main thread when buffering is disabled.
   at MS.Internal.InternalNetworkStream.Read(Byte[] buffer, Int32 offset, Int32 count)
   at System.Windows.Media.Imaging.BitmapSource.ReadStream(Stream streamSource, Byte[]& buffer, Int32& position)
   at System.Windows.Media.Imaging.BitmapSource.SetSourceInternal(Stream streamSource)
   at System.Windows.Media.Imaging.BitmapImage.SetSourceInternal(Stream streamSource)
   at System.Windows.Media.Imaging.BitmapSource.SetSource(Stream streamSource)
   at ToonGui.ImportImageDialog.<>c__DisplayClass2.<OKButton_Click>b__1()}
    [System.NotSupportedException]: {System.NotSupportedException: Read is not supported on the main thread when buffering is disabled.
   at MS.Internal.InternalNetworkStream.Read(Byte[] buffer, Int32 offset, Int32 count)
   at System.Windows.Media.Imaging.BitmapSource.ReadStream(Stream streamSource, Byte[]& buffer, Int32& position)
   at System.Windows.Media.Imaging.BitmapSource.SetSourceInternal(Stream streamSource)
   at System.Windows.Media.Imaging.BitmapImage.SetSourceInternal(Stream streamSource)
   at System.Windows.Media.Imaging.BitmapSource.SetSource(Stream streamSource)
   at ToonGui.ImportImageDialog.<>c__DisplayClass2.<OKButton_Click>b__1()}
    Data: {System.Collections.ListDictionaryInternal}
    InnerException: null
    Message: "Read is not supported on the main thread when buffering is disabled."
    StackTrace: "   at MS.Internal.InternalNetworkStream.Read(Byte[] buffer, Int32 offset, Int32 count)\r\n   at System.Windows.Media.Imaging.BitmapSource.ReadStream(Stream streamSource, Byte[]& buffer, Int32& position)\r\n   at System.Windows.Media.Imaging.BitmapSource.SetSourceInternal(Stream streamSource)\r\n   at System.Windows.Media.Imaging.BitmapImage.SetSourceInternal(Stream streamSource)\r\n   at System.Windows.Media.Imaging.BitmapSource.SetSource(Stream streamSource)\r\n   at ToonGui.ImportImageDialog.<>c__DisplayClass2.<OKButton_Click>b__1()"

Do I have to use a BackgroundWorker class to let the downloading task run in another thread?

Answer 1

Thank you guys, I finally found the answer. It's a Siverlight bug, which is Microsoft's fault.

As one of my friends said 微软。。。总是有一堆令人想杀人的问题 (which means Microsoft.... always has some issues that drive you crazy enough so that you want to shoot someone)

The cause is from the theProgressBarDialog which is a ChildWindow, which haa a stupid bug: after closing, sometime it leaves the parent window (the main app) disabled.

1. Silverlight: Modal ChildWindow keeps parent grayed after closing: (Also try calling this.DialogResult = true instead of the Close method.) Silverlight: Modal ChildWindow keeps parent grayed after closing

2. Silverlight 4 ChildWindow leaves parent disabled after closing: http://social.msdn.microsoft.com/Forums/en-US/silverlightbugs/thread/56d0dc0b-3711-4643-b56f-2c94344e3d3a/

The solution is:

        private void ChildWindow_Closed(object sender, System.EventArgs e)
        {
// TODO: should we use apply this fix to all ChildWindow? (make a TnChildWindow)
//   1. Silverlight: Modal ChildWindow keeps parent grayed after closing:
//      (Also try calling this.DialogResult = true instead of the Close method.)
//      https://stackoverflow.com/questions/6456952/silverlight-modal-childwindow-keeps-parent-grayed-after-closing
//   2. Silverlight 4 ChildWindow leaves parent disabled after closing:
//      http://social.msdn.microsoft.com/Forums/en-US/silverlightbugs/thread/56d0dc0b-3711-4643-b56f-2c94344e3d3a/
            Application.Current.RootVisual.SetValue(Control.IsEnabledProperty, true);
        }