Invoke() and BeginInvoke()

What's the difference between Invoke() and BeginInvoke()

Delegate.Invoke/BeginInvoke and Control.Invoke/BeginInvoke

Delegate.Invoke: Executes synchronously, on the same thread.
Delegate.BeginInvoke: Executes asynchronously, on a threadpool thread.

Control.Invoke: Executes on the UI thread, but calling thread waits for completion before continuing.
Control.BeginInvoke: Executes on the UI thread, and calling thread doesn't wait for completion.

A logical conclusion is that a delegate you pass to Invoke() can have out-parameters or a return-value, while a delegate you pass to BeginInvoke() cannot (you have to use EndInvoke to retrieve the results).

 new Thread(foo).Start();     private void foo()     {     this.Dispatcher.BeginInvoke(DispatcherPriority.Normal,     (ThreadStart)delegate()     {     myTextBox.Text = "bing";     Thread.Sleep(TimeSpan.FromSeconds(3));     });     MessageBox.Show("done");     } 

If use BeginInvoke, MessageBox pops simultaneous to the text update. If use Invoke, MessageBox pops after the 3 second sleep. Hence, showing the effect of an asynchronous (BeginInvoke) and a synchronous (Invoke) call.

Delegate.BeginInvoke() asynchronously queues the call of a delegate and returns control immediately. When using Delegate.BeginInvoke(), you should call Delegate.EndInvoke() in the callback method to get the results.

Delegate.Invoke() synchronously calls the delegate in the same thread.

why and when to use Invoke().

Both Invoke() and BeginInvoke() marshal the code you specify to the dispatcher thread.

But unlike BeginInvoke(), Invoke() stalls your thread until the dispatcher executes your code. You might want to use Invoke() if you need to pause an asynchronous operation until the user has supplied some sort of feedback.

For example, you could call Invoke() to run a snippet of code that shows an OK/Cancel dialog box. After the user clicks a button and your marshaled code completes, the invoke() method will return, and you can act upon the user's response.