Question

I’m trying to call Dispatcher.PushFrame() from several different thread but encounter an error:

Must create DependencySource on same
Thread as the DependencyObject.

Here is a code snippet:

_lockFrame = new DispatcherFrame(true);
Dispatcher.PushFrame(_lockFrame);

When I tried:

Dispatcher.CurrentDispatcher.Invoke(
    DispatcherPriority.Normal,
    new Action(() => _lockFrame = new DispatcherFrame(true));
Dispatcher.PushFrame(_lockFrame);

I get the error:

Objects must be created by the same
thread.

What is the approach for pushing multiple frames into the Dispatcher from different threads?

Answer 1

Each thread has its own dispatcher object – returned by Dispatcher.CurrentDispatcher

The approach would be to cache the target dispatcher object once by calling the above method on the UI Thread. Then use _cachedObj.Invoke like you have – to marshal it across to the right thread.

WPF UI has ‘thread affinity’ – UI can only be accessed by the thread that creates it.

Update: Not sure of what you’re trying to achieve. But the following code-snippet worked for me.

    private Dispatcher _dispatcher;
    private DispatcherFrame _lockFrame;
    public Window1()
    {
        InitializeComponent();

        _dispatcher = Dispatcher.CurrentDispatcher;

        // the other thread
        Thread t = new Thread(
            (ThreadStart)delegate
            {

                _dispatcher.Invoke(
                    (Action)delegate
                    {
                        var frame = CreateNewFrame();
                        Dispatcher.PushFrame(frame);
                    });
            });
        t.Start();