Dispatcher.CheckAccess 方法

定义

确定调用线程是否为与此 Dispatcher 关联的线程。

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

返回

如果调用线程是与此 Dispatcher 关联的线程,则为 true;否则为 false

示例

以下示例使用 CheckAccess 确定线程是否有权访问 ButtonCheckAccess调用与 Button 关联的 上的 Dispatcher 方法以验证对线程的访问。 如果调用线程有权访问 DispatcherButton 则通过访问 的成员 Button来更新 ;否则,接受 Button 作为参数的委托将放在 上 Dispatcher。 将 Dispatcher 委托更新 的工作 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

Dispatcher DispatcherObject只有创建 上的 可以访问 对象。 使用 InvokeBeginInvoke 从其他线程访问 对象。

CheckAccess 可以从任何线程调用。

VerifyAccess 之间的CheckAccessCheckAccess差返回一个布尔值,指示调用线程是否有权访问 DispatcherVerifyAccess引发异常。

适用于

另请参阅