Dispatcher.CheckAccess 方法

定义

确定调用线程是否为与此 Dispatcher 关联的线程。Determines whether the calling thread is the thread associated with this Dispatcher.

public:
 bool CheckAccess();
public bool CheckAccess ();
member this.CheckAccess : unit -> bool
Public Function CheckAccess () As Boolean

返回

Boolean

如果调用线程是与此 Dispatcher 关联的线程,则为 true;否则为 falsetrue if the calling thread is the thread associated with this Dispatcher; otherwise, false.

示例

下面的示例使用 CheckAccess 来确定线程是否有权访问 ButtonThe following example uses CheckAccess to determine whether a thread has access to a Button. CheckAccess Dispatcher 调用与关联的的方法 Button 来验证对线程的访问。The CheckAccess method on the Dispatcher associated with the Button is called to verify access to the thread. 如果调用线程具有对的访问权限 Dispatcher ,则将 Button 通过访问的成员进行更新 Button ; 否则,会将接受作为参数的委托 Button 置于上 DispatcherIf 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. Dispatcher将委托更新的工作 ButtonThe 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);
        }
    }
}
' Uses the Dispatcher.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.Dispatcher.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.
            ' Place the 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 Dispatcher DispatcherObject 在上创建的可以访问对象。Only the Dispatcher that a DispatcherObject is created on may access the object. 使用 InvokeBeginInvoke 从其他线程访问对象。Use Invoke or BeginInvoke to access the object from a different thread.

CheckAccess 可以从任何线程调用。CheckAccess can be called from any thread.

与之间的 CheckAccess 差异 VerifyAccessCheckAccess 返回一个布尔值,该值指示调用线程是否有权访问 DispatcherVerifyAccess 引发异常。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.

适用于

另请参阅