WPF Access window created on different UI thread

Question

I created new Window on a different thread because it has heavy UI operations, that was done to keep my main window run smoothly. Everything works perfectly.

But here is the question:
How I can access newly created window?
After calling Dispatcher.Run() I can not manipulate visualisationWindow anymore. I want to keep access to that newly created window object.

Here is how my window created:

 private void CreateVisualisationWindow() { Thread VisualisationWIndowThread = new Thread(new ThreadStart(ThreadStartingPoint)); VisualisationWIndowThread.SetApartmentState(ApartmentState.STA); VisualisationWIndowThread.IsBackground = true; VisualisationWIndowThread.Start(); } private void ThreadStartingPoint() { Visualisation visualisationWindow = new Visualisation(); visualisationWindow.Show(); System.Windows.Threading.Dispatcher.Run(); }

Also I tried accessing it through System.Windows.Threading.Dispatcher.FromThread(VisualisationWIndowThread) but seems I misunderstand some core things.

Using multiple ui threads is one of those things you can do technically BUT is almost always a bad idea. I think a different approach with one ui thread is probably a better plan. What does your visualisation window actually do? As an alternative, why do you need to access the actual window? I would expect to work with some sort of UI agnostic viewmodel which CAN deal with multiple threads. — Andy
– Andy, Commented Dec 5, 2018 at 10:09
@Andy, there are multiple ui threads only because second window includes WinForms element that using UI thread heavily (screenBG.Render() where screenBG is of BufferedGraphics type - that mehtod can only be executed on UI thread) and there is no way to avoid it even with async approach. It is used to display some science data — Stanislav Kholodov
– Stanislav Kholodov, Commented Dec 5, 2018 at 10:48
I'm not familiar with screenbg.render. Do you have to use that? I was thinking maybe writeablebitmap. Process on a backround thread, translate to bitmap, freeze and pass back. Although.... Just building a wbm is very fast so long as you free up the ui thread a little between changes you can construct very quickly changing images. — Andy
– Andy, Commented Dec 5, 2018 at 19:31

Coops · Accepted Answer · 2018-12-05 13:13:43Z

I simulated your issue using two WPF Window objects and a timer to ensure that the Second Window was created before calling operations on it. Below is my code sample and it updates the second Windows TextBox every five seconds:

 private Timer _timer; private SecondWindow _secondWindow; public MainWindow() { InitializeComponent(); CreateVisualisationWindow(); _timer = new Timer(Callback); _timer.Change(5000, 5000); } private void Callback(object state) { UpdateSecondWindowText(); } private void CreateVisualisationWindow() { Thread VisualisationWIndowThread = new Thread(ThreadStartingPoint); VisualisationWIndowThread.SetApartmentState(ApartmentState.STA); VisualisationWIndowThread.IsBackground = true; VisualisationWIndowThread.Start(); } private void ThreadStartingPoint() { _secondWindow = new SecondWindow(); _secondWindow.SecondWindowTextBlock.Text = "Hello"; _secondWindow.Show(); Dispatcher.Run(); } private void UpdateSecondWindowText() { _secondWindow.Dispatcher.BeginInvoke(new Action(() => { _secondWindow.SecondWindowTextBlock.Text = _secondWindow.SecondWindowTextBlock.Text + " World"; })); }

So the trick is, you need to call the Dispatcher on the second Window in order to gain access to it.

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