Executes the specified delegate asynchronously with the specified arguments on the thread that the Dispatcher was created on.
Assembly: WindowsBase (in WindowsBase.dll)
Public Function BeginInvoke ( _ method As Delegate, _ ParamArray args As Object() _ ) As DispatcherOperation
public DispatcherOperation BeginInvoke( Delegate method, params Object[] args )
public:
DispatcherOperation^ BeginInvoke(
Delegate^ method,
... array<Object^>^ args
)
member BeginInvoke : method:Delegate * args:Object[] -> DispatcherOperation
Parameters
- method
- Type: System.Delegate
The delegate to a method that takes parameters specified in args, which is pushed onto the Dispatcher event queue.
- args
- Type: System.Object[]
An array of objects to pass as arguments to the given method. Can be null.
Return Value
Type: System.Windows.Threading.DispatcherOperationAn object, which is returned immediately after BeginInvoke is called, that can be used to interact with the delegate as it is pending execution 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.
BeginInvoke is asynchronous; therefore, control returns immediately to the calling object after it is called.
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.
If BeginInvoke is called on a Dispatcher that has shut down, the status property of the returned DispatcherOperation is set to Aborted.
.NET Framework
Supported in: 4, 3.5 SP1, 3.0 SP2.NET Framework Client Profile
Supported in: 4, 3.5 SP1Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Reference
Other Resources
After starting a thread to do some background work, it is often necessary to provide a visual cue to the user that the work has completed. Performing long-running activities on the foreground UI thread can result in an application that looks like it has died after a user initiated request, which creates a poor application experience. However, starting a thread on-demand in a click event handler can cause other issues if an impatient user repeatedly presses the "do it now" button. One simple solution for this problem is to disable the button and set its content to a brief status message (like, Saving...) in the click handler, and then starting a thread to do the long part of the work (using ThreadPool.QueueUserWorkItem, for example) before returning.
It then becomes necessary to reenable the button and restore the text content from the worker thread when it completes, but since this thread doesn't own the control, it will be prevented from doing so directly. An Action generic delegate that encapsulates a statement lambda can be used with Dispatcher.BeginInvoke to yield a compact and concise method for accomplishing the required task:
Action act = () => {
saveButton.Content = "Save";
saveButton.IsEnabled = true;
};
this.Dispatcher.BeginInvoke(act);