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.
BeginInvoke is asynchronous; therefore, control returns immediately to the calling object after it is called.
BeginInvoke returns a DispatcherOperation object that can be used to interact with the delegate when the delegate is in the event queue.
The DispatcherOperation object returned by BeginInvoke can be used in several ways to interact with the specified delegate, such as:
Changing the DispatcherPriority of the delegate as it is pending execution in the event queue.
Removing the delegate from the event queue.
Waiting for the delegate to return.
Obtaining the value that the delegate returns after it is executed.
If multiple BeginInvoke calls are made at the same DispatcherPriority, they will be executed in the order the calls were made.
If BeginInvoke is called on a Dispatcher that has shut down, the status property of the returned DispatcherOperation is set to Aborted.