Running a WPF control in another thread

Question

I am using a visual control in my project that is from a library that I do not have the source to.
It takes too long to update (200ms, roughly) for good UI responsivenes

Answer 1

Well, I have a method that works - but it may well not be the most elegant..

I have a window that contains my third party (slow-rendering) control in the XAML.

public partial class MapWindow : Window
{
    private ConcurrentQueue _mapCommandQueue;
    private HwndSource _source;

    // ...

}

My main (UI) thread contructs and starts this window on a thread:

_leftTopThread = new Thread(() =>
{
   _topLeftMap = new MapWindow()
   {
      WindowStartupLocation = WindowStartupLocation.Manual,
      CommandQueue = _leftMapCommendQueue,
   };

    _topLeftMap.Show();
    System.Windows.Threading.Dispatcher.Run();

});

_leftTopThread.SetApartmentState(ApartmentState.STA);
_leftTopThread.IsBackground = true;
_leftTopThread.Name = "LeftTop";
_leftTopThread.Start();

I then get a handle to the window in the thread (after it has initialised):

private IntPtr LeftHandMapWindowHandle
{
    get
    {
        if (_leftHandMapWindowHandle == IntPtr.Zero)
        {
            if (!_topLeftMap.Dispatcher.CheckAccess())
            {
                _leftHandMapWindowHandle = (IntPtr)_topLeftMap.Dispatcher.Invoke(
                  new Func(() => new WindowInteropHelper(_topLeftMap).Handle)
                );
            }
            else
            {
                _leftHandMapWindowHandle = new WindowInteropHelper(_topLeftMap).Handle;
            }
        }
        return _leftHandMapWindowHandle;
    }
}

.. and after putting a command onto the thread-safe queue that is shared with the threaded window:

var command = new MapCommand(MapCommand.CommandType.AircraftLocation, new object[] {RandomLatLon});
_leftMapCommendQueue.Enqueue(command);

.. I let it know it can check the queue:

PostMessage(LeftHandMapWindowHandle, MapWindow.WmCustomCheckForCommandsInQueue, IntPtr.Zero, IntPtr.Zero);

The window can receive my message because it has hooked into the window messages:

protected override void OnSourceInitialized(EventArgs e)
{
    base.OnSourceInitialized(e);

    _source = PresentationSource.FromVisual(this) as HwndSource;
    if (_source != null) _source.AddHook(WndProc);
}

..which it then can check:

private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled) // 
{
    // Handle messages...
    var result = IntPtr.Zero;

    switch (msg)
    {
        case WmCustomCheckForCommandsInQueue:
            CheckForNewTasks();
            break;

    }
    return result;
}

..and then execute on the thread!

private void CheckForNewTasks()
{
    MapCommand newCommand;
    while (_mapCommandQueue.TryDequeue(out newCommand))
    {
        switch (newCommand.Type)
        {
            case MapCommand.CommandType.AircraftLocation:
                SetAircraftLocation((LatLon)newCommand.Arguments[0]);
                break;

            default:
                Console.WriteLine(String.Format("Unknown command '0x{0}'for window", newCommand.Type));
                break;
        }
    }
}

Easy as that.. :)