DispatcherObject.CheckAccess Method
Definition
Important
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Determines whether the calling thread has access to this DispatcherObject.
public:
bool CheckAccess();
public bool CheckAccess ();
member this.CheckAccess : unit -> bool
Public Function CheckAccess () As Boolean
Returns
true
if the calling thread has access to this object; otherwise, false
.
Examples
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 void TryToUpdateButtonCheckAccess(object uiObject)
{
Button theButton = uiObject as Button;
if (theButton != null)
{
// Checking if this thread has access to the object
if(theButton.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
// Pushing update method on the Dispatcher of the UI thread
theButton.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
new UpdateUIDelegate(UpdateButtonUI), theButton);
}
}
}
' 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
Remarks
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.
Applies to
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