WPF: issue updating UI from background thread
- by Ted Shaffer
My code launches a background thread. The background thread makes changes and wants the UI in the main thread to update. The code that launches the thread then waits looks something like:
Thread fThread = new Thread(new ThreadStart(PerformSync));
fThread.IsBackground = true;
fThread.Start();
fThread.Join();
MessageBox.Show("Synchronization complete");
When the background wants to update the UI, it sets a StatusMessage and calls the code below:
static StatusMessage _statusMessage;
public delegate void AddStatusDelegate();
private void AddStatus()
{
AddStatusDelegate methodForUIThread = delegate
{
_statusMessageList.Add(_statusMessage);
};
this.Dispatcher.BeginInvoke(methodForUIThread, System.Windows.Threading.DispatcherPriority.Send);
}
_statusMessageList is an ObservableCollection that is the source for a ListBox.
The AddStatus method is called but the code on the main thread never executes - that is, _statusMessage is not added to _statusMessageList while the thread is executing. However, once it is complete (fThread.Join() returns), all the stacked up calls on the main thread are executed.
But, if I display a message box between the calls to fThread.Start() and fThread.Join(), then the status messages are updated properly.
What do I need to change so that the code in the main thread executes (UI updates) while waiting for the thread to terminate?
Thanks.
