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DispatcherObject.CheckAccess Method

Determines whether the calling thread has access to this DispatcherObject.

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

'Declaration
Public Function CheckAccess As Boolean

Return Value

Type: System.Boolean
true if the calling thread has access to this object; otherwise, false.

Only the thread the Dispatcher was created on may access the DispatcherObject.

Any thread can check to see whether it has access to this DispatcherObject.

The difference between CheckAccess and VerifyAccess is that CheckAccess returns a Boolean that specifies whether the calling thread has access to this DispatcherObject and VerifyAccess throws an exception if the calling thread does not have access to the this DispatcherObject.

Calling this method is identical to calling CheckAccess on the associated Dispatcher object.

The following example uses CheckAccess to determine whether a thread has access to the thread that a Button was created on. The CheckAccess method on the Button is called to verify access to the thread. If the calling thread has access, the Button is updated by just accessing the members of the Button; otherwise, a delegate, which accepts a Button as an argument, is posted onto the Dispatcher of the Button.

		' Uses the DispatcherObject.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.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
					' Pushing 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

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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