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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 bool CheckAccess ()
public boolean CheckAccess ()
public function CheckAccess () : boolean
You cannot use methods in XAML.

Return Value

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

Only the Dispatcher that a DispatcherObject is crated 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 void TryToUpdateButtonCheckAccess(object uiObject)
{
    Button theButton = uiObject as Button;

    if (theButton != null)
    {
        // Checking if this thread has access to the object.
        if (theButton.Dispatcher.CheckAccess())
        {
            // 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(UpdateButtonUI), theButton);
        }
    }
}

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0

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