DispatcherObject.CheckAccess DispatcherObject.CheckAccess DispatcherObject.CheckAccess DispatcherObject.CheckAccess Method

定义

确定调用线程是否可以访问此 DispatcherObjectDetermines 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

返回

如果调用线程可以访问此对象,则为 true;否则,为 falsetrue if the calling thread has access to this object; otherwise, false.

示例

下面的示例使用CheckAccess来确定线程是否具有访问该线程的Button上创建。The following example uses CheckAccess to determine whether a thread has access to the thread that a Button was created on. CheckAccess方法Button调用以验证是否可以访问该线程。The CheckAccess method on the Button is called to verify access to the thread. 如果调用线程具有访问权限,Button只需访问的成员更新Button; 否则为一个委托,它接受Button作为参数,发布到DispatcherButtonIf 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

注解

只有线程Dispatcher创建在可访问DispatcherObjectOnly the thread the Dispatcher was created on may access the DispatcherObject.

任何线程可以检查以查看其是否具有访问此DispatcherObjectAny thread can check to see whether it has access to this DispatcherObject.

之间的差异CheckAccessVerifyAccess在于CheckAccess返回一个布尔值,指定调用线程是否具有访问此DispatcherObjectVerifyAccess将引发异常,如果调用线程不具有访问这DispatcherObjectThe 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.

调用此方法等同于调用CheckAccess关联Dispatcher对象。Calling this method is identical to calling CheckAccess on the associated Dispatcher object.

适用于