Dispatcher.CheckAccess Method ()

 

Determines whether the calling thread is the thread associated with this Dispatcher.

Namespace:   System.Windows.Threading
Assembly:  WindowsBase (in WindowsBase.dll)

Public Function CheckAccess As Boolean

Return Value

Type: System.Boolean

true if the calling thread is the thread associated with this Dispatcher; otherwise, false.

Only the Dispatcher that a DispatcherObject is created on may access the object. Use Invoke or BeginInvoke to access the object from a different thread.

CheckAccess can be called from any thread.

The difference between CheckAccess and VerifyAccess is CheckAccess returns a Boolean indicating whether the calling thread has access to the Dispatcher and VerifyAccess throws an exception.

The following example uses CheckAccess to determine whether a thread has access to a Button. The CheckAccess method on the Dispatcher associated with the Button is called to verify access to the thread. If the calling thread has access to the Dispatcher, the Button is updated by accessing the members of the Button; otherwise, a delegate, which accepts a Button as an argument, is placed onto the Dispatcher. The Dispatcher will delegate the work of updating the Button.

' Uses the Dispatcher.CheckAccess method to determine if 
' the calling thread has access to the thread the UI object is on.
Private Sub TryToUpdateButtonCheckAccess(ByVal uiObject As Object)
	Dim theButton As Button = TryCast(uiObject, Button)

	If theButton IsNot Nothing Then
		' Checking if this thread has access to the object.
		If theButton.Dispatcher.CheckAccess() Then
			' This thread has access so it can update the UI thread.
			UpdateButtonUI(theButton)
		Else
			' This thread does not have access to the UI thread.
			' Place the update method on the Dispatcher of the UI thread.
			theButton.Dispatcher.BeginInvoke(DispatcherPriority.Normal, New UpdateUIDelegate(AddressOf UpdateButtonUI), theButton)
		End If
	End If
End Sub

.NET Framework
Available since 3.0
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
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