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Dispatcher.VerifyAccess Method

Determines whether the calling thread has access to this Dispatcher.

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

public void VerifyAccess()
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ExceptionCondition
InvalidOperationException

The calling thread does not have access to this Dispatcher.

Only the thread the Dispatcher is created on may access the Dispatcher.

This method is public; therefore, any thread can check to see whether it has access to the Dispatcher.

The difference between CheckAccess and VerifyAccess is CheckAccess returns a Boolean if the calling thread does not have access to the Dispatcher and VerifyAccess throws an exception.

The following example uses VerifyAccess to determine whether a thread has access to the thread that a Button was created on. The method takes an object as an argument, which is cast to a Button. The VerifyAccess method on the Dispatcher of the Button is called to verify access to the thread.

If the calling thread has access to the Dispatcher, the Button is updated by just accessing the members of the Button.

If the calling thread does not have access, an InvalidOperationException is thrown. This example catches the exception and pushes a delegate, which accepts a Button as an argument, onto the Dispatcher of the Button. This Dispatcher will do the work of updating the Button.

// Check if this thread has access to this object.
theButton.Dispatcher.VerifyAccess();

// The thread has access to the object, so update the UI.
UpdateButtonUI(theButton);

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

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

.NET Framework

Supported in: 3.5, 3.0
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