DispatcherObject.CheckAccess 方法

public:
 bool CheckAccess();

public bool CheckAccess();

member this.CheckAccess : unit -> bool

Public Function CheckAccess () As Boolean

返回

true 如果调用线程有权访问此对象，则为 ;否则，为 false.

示例

以下示例用于 CheckAccess 确定线程是否有权访问创建线程的线程 Button 。 调用 CheckAccess 该方法 Button 以验证对线程的访问。 如果调用线程具有访问权限， Button 则只需访问成员 Button即可更新该线程;否则，接受 Button 作为参数的委托将 Dispatcher 发布到其中 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

注解

只有创建时创建的线程才能访问该Dispatcher线程DispatcherObject。

任何线程都可以检查它是否有权访问此 DispatcherObject线程。

区别在于CheckAccessVerifyAccessCheckAccess，返回一个布尔值，该值指定调用线程是否有权访问此对象，并在DispatcherObject调用线程无权VerifyAccess访问此DispatcherObject对象时引发异常。

调用此方法与调用 CheckAccess 关联的 Dispatcher 对象相同。