Handling a second UI thread in WPF

Question

I have a long running process that runs on my UI thread that I cannot move off of the UI thread. Instead I am trying to create a second UI thread that has a waiting animation. Here's the code I'm using to create the second UI thread:

Private _busyThread As Thread
Private _waitWindow As WaitWindow 'This is the window with the animation

Private Sub StartBusyIndicator(ByVal busyInfo As BusyInfo)
    _busyThread = New Thread(New ThreadStart(AddressOf ThreadStartingPoint))
    _busyThread.SetApartmentState(ApartmentState.STA)
    _busyThread.IsBackground = True
    _busyThread.Start()
End Sub

Private Function ThreadStartingPoint() As ThreadStart
    _waitWindow = New WaitWindow
    _waitWindow.Show()
    System.Windows.Threading.Dispatcher.Run()
End Function

How can I close this gracefully when needed? I can't access _waitWindow from the main UI thread to close it. If I issue _busyThread.Abort() it doesn't actually close the window.

Answer 1

You would need to use Dispatcher.BeginInvoke to close the window:

This marshals the call to close the window into the new window's thread.

This will not shut down that thread, though. To do that, try:

_waitWindow.Dispatcher.BeginInvoke(Sub()
         _waitWindow.Dispatcher.BeginInvokeShutdown(DispatcherPriority.Background)
         _waitWindow.Close()
    End Sub)

I have an article on my blog which discusses this, as well as other issues, in detail. It's in C#, but could be converted to VB.Net easily enough.

Note that, in the long run, figuring out how to move the long running process off the main thread will be a better solution, as this will still leave your application as appearing unresponsive to Windows and your end user.