In WPF, only the thread that created a DispatcherObject may access that object. For example, a background thread that is spun off from the main UI thread cannot update the contents of a Button that was created on the UI thread. In order for the background thread to access the Content property of the Button, the background thread must delegate the work to the Dispatcher associated with the UI thread. This is accomplished by using either Invoke or BeginInvoke. Invoke is synchronous and BeginInvoke is asynchronous. The operation is added to the event queue of the Dispatcher at the specified DispatcherPriority.

Invoke is a synchronous operation; therefore, control will not return to the calling object until after the callback returns.

The following example places a delegate onto a Dispatcher at Normal using Invoke. For the full source of the example, see Disable Command Source via Dispatcher Timer Sample.

// Places the delegate onto the UI Thread's Dispatcher
private void timer_Elapsed(object sender, ElapsedEventArgs e)
{
    // Place delegate on the Dispatcher.
    this.Dispatcher.Invoke(DispatcherPriority.Normal,
        new TimerDispatcherDelegate(TimerWorkItem));
}

Reference