if the main thread is STA and creates a Window, adds some UI elements to it. Then spawns off another STA thread, and that second thread likewise creates some UI elements, are they doing it in the same 'space' [snip...] and can access each other's UI elements without causing death and destruction?
If Thread A and B are both STA, then they can each create and update their own UI elements, but not eachothers. Any other threads that want to affect the UI have to use one of the BeginInvoke
style methods to ask the appropriate thread to do the update.
If it is not necessary, then I will just make that worker thread an STA thread and continue on my way, is that fair? Or am I courting disaster?
You may not be able to make the worker thread an STA thread if it's been set to MTA and initialized. You may have to make a new thread.
How do you do it? It seems like you want to use WPF (System.Windows.*
) for your UI - so If the app that you are "plugging into" is also using WPF, you should be able to access it and re use it's UI thread. If not, you can make a new thread, and create a new Application
on it and call Run
. This should set up a dispatcher for you.
Something like this (pseudo code sort-of copied from some working code I have elsewhere)
Dispatcher dispatcher = null; // we 'get to' the UI thread via the dispatcher
if(Application.Current) { // re use an existing application's UI thread
dispatcher = Application.Current.Dispatcher;
} else {
var threadReadyEvent = new ManualResetEvent(false);
var uiThread = new Thread(() => {
Thread.CurrentThread.SetApartmentState(ApartmentState.STA);
var application = new Application();
application.Startup += (sender, args) => {
dispatcher = application.Dispatcher;
threadReadyEvent.Set();
};
// apps have to have a "main window" - but we don't want one, so make a stub
var stubWindow = new Window {
Width = 1, Height = 1,
ShowInTaskbar = false, AllowsTransparency = true,
Background = Brushes.Transparent, WindowStyle = WindowStyle.None
};
application.Run(stubWindow);
}){ IsBackground = true };
uiThread.Start();
threadReadyEvent.WaitOne();
threadReadyEvent.Dispose();
}
dispatcher.Invoke(() => {
// ask the UI thread to do something and block until it finishes
});
dispatcher.BeginInvoke(() => {
// ask the UI thread to do something asynchronously
});
and so forth