For a WPF application, is there internally a classic message loop (in Windows's GetMessage/DispatchMessage sense), inside Application.Run? Is it possible to catch a message posted from another Win32 application with PostThreadMessage to a WPF UI thread (a message without HWND handle). Thank you.
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2It might be possible to watch for a specific message with ComponentDispatcher.ThreadFilterMessage event, although the docs say it's intended for keyboard messages. Here's a related question answered.noseratio– noseratio2013-08-12 09:00:56 +00:00Commented Aug 12, 2013 at 9:00
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1 Answer
I used .NET Reflector to track the Applicaton.Run implementation down to Dispatcher.PushFrameImpl. It's also possible to obtain the same information from .NET Framework reference sources. There is indeed a classic message loop:
private void PushFrameImpl(DispatcherFrame frame)
{
SynchronizationContext syncContext = null;
SynchronizationContext current = null;
MSG msg = new MSG();
this._frameDepth++;
try
{
current = SynchronizationContext.Current;
syncContext = new DispatcherSynchronizationContext(this);
SynchronizationContext.SetSynchronizationContext(syncContext);
try
{
while (frame.Continue)
{
if (!this.GetMessage(ref msg, IntPtr.Zero, 0, 0))
{
break;
}
this.TranslateAndDispatchMessage(ref msg);
}
if ((this._frameDepth == 1) && this._hasShutdownStarted)
{
this.ShutdownImpl();
}
}
finally
{
SynchronizationContext.SetSynchronizationContext(current);
}
}
finally
{
this._frameDepth--;
if (this._frameDepth == 0)
{
this._exitAllFrames = false;
}
}
}
Further, here's the implementation of TranslateAndDispatchMessage, which indeed fires ComponentDispatcher.ThreadFilterMessage event along its course of execution inside RaiseThreadMessage:
private void TranslateAndDispatchMessage(ref MSG msg)
{
if (!ComponentDispatcher.RaiseThreadMessage(ref msg))
{
UnsafeNativeMethods.TranslateMessage(ref msg);
UnsafeNativeMethods.DispatchMessage(ref msg);
}
}
Apparently, it works for any posted message, not just keyboard ones. You should be able to subscribe to ComponentDispatcher.ThreadFilterMessage and watch for your message of interest.
