WPF calls not working during long method processing

Question

Hi, The following method does not apply the wpf changes (background = red) until the 2nd method (DoWork) exits:

private void change()
{
    Background = Brushes.Red;
    Dispatcher.BeginInvoke((Action) DoWork);
}

DoWork() takes several seconds to run and I don't really want to put it into a thread, as this code will be used in several places and will probably interact will the Dispatcher thread at various intervals. I've tried calling the Invalidate...() methods, but to no avail. The BeginInvoke() was added to see if the delay would allow the background change to be applied before the logic was called. Typically, the logic would be part of this method. Btw, most of the logic is performed on a different thread and shouldn't block the Dispatcher thread?!

Can someone please help? Thanks

Answer 1

The "Dispatcher" thread is the UI thread.

When you call Dispatcher.BeginInvoke((Action) DoWork);, you're basically blocking the UI thread until DoWork exits, since it's running on the UI thread.

This will prevent the UI from updating, hence you don't see the background change.

You really should consider moving DoWork onto a background thread, either via the ThreadPool directly, a BackgroundWorker, or some other means. That would completely correct this problem, and prevent you from blocking the UI thread for a "few seconds" (which will happen if you run this using the Dispatcher's threading).

Answer 2

I tried to use the background threaded approach, however this raises problem where changes to the UI are attempted outside of the Dispatcher thread. For example, variables bound to user controls are fired in the DoWork() method, which throw exceptions due to not being executed in the Dispatcher thread. The above approach also means that any change to the UI from DoWork() must be wrapped in a Dispatcher.(Begin)Invoke() call, which means bloated code. There must be a different way to do this?!

Thanks

Answer 3

for communication between thread we haev Dispatcher class in WPF

Dispatcher.Invoke(DispatcherPriority.Normal, (NoArgDelegate)delegate { ------ });