Dispatcher.BeginInvoke Method (DispatcherPriority, Delegate, Object)
Executes the specified delegate asynchronously at the specified priority and with the specified argument on the thread the Dispatcher is associated with.
Assembly: WindowsBase (in WindowsBase.dll)
<BrowsableAttribute(False)> Public Function BeginInvoke ( priority As DispatcherPriority, method As Delegate, arg As Object ) As DispatcherOperation
The priority, relative to the other pending operations in the Dispatcher event queue, the specified method is invoked.
A delegate to a method that takes one argument, which is pushed onto the Dispatcher event queue.
The object to pass as an argument to the specified method.
Arg can be null if no arguments are needed.
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.
The following example shows how to place an operation onto a Dispatcher.
First, a delegate is created that accepts one argument, in this case a string.
Next, DispatcherObject has a property that returns the Dispatcher it is associated with, the desired Dispatcher is obtained by querying the DispatcherObject, in this case a Grid named tomorrowsWeather. The call to takes three parameters: the priority, which is set to DispatcherPriority.Normal; the callback, which is passed in through an instance of the delegate OneArgDelegate; and a string named weather, which is the argument for the callback.is called. Because every
Available since 3.0