Dispatcher.Invoke Method (DispatcherPriority, TimeSpan, Delegate, Object, Object())
Executes the specified delegate at the specified priority with the specified arguments synchronously on the thread the Dispatcher is associated with.
Assembly: WindowsBase (in WindowsBase.dll)
'Declaration <BrowsableAttribute(False)> _ Public Function Invoke ( _ priority As DispatcherPriority, _ timeout As TimeSpan, _ method As Delegate, _ arg As Object, _ ParamArray args As Object() _ ) As Object
- Type: System.Windows.Threading.DispatcherPriority
The priority, relative to the other pending operations in the Dispatcher event queue, the specified method is invoked.
- Type: System.TimeSpan
The maximum time to wait for the operation to finish.
- Type: System.Delegate
A delegate to a method that takes multiple arguments, which is pushed onto the Dispatcher event queue.
- Type: System.Object
An object to pass as an argument to the specified method.
- Type: System.Object()
An array of objects to pass as arguments to the specified method.
Return ValueType: System.Object
The return value from the delegate being invoked or Nothing if the delegate has no return value.
Arg can be Nothing if an argument is not needed.
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.