DispatcherObject.CheckAccess 方法

定义

命名空间:

System.Windows.Threading

程序集:

WindowsBase.dll

确定调用线程是否可以访问此 DispatcherObject。

public:
 bool CheckAccess();

public bool CheckAccess ();

member this.CheckAccess : unit -> bool

Public Function CheckAccess () As Boolean

返回

Boolean

如果调用线程可以访问此对象，则为 true；否则，为 false。

示例

以下示例使用 CheckAccess 来确定线程是否有权访问创建 的线程 Button 。 CheckAccess调用 上的 Button 方法以验证对线程的访问。 如果调用线程具有访问权限， Button 则仅通过访问 的成员 Button来更新 ;否则，接受 Button 作为参数的 委托将发布到 Dispatcher 的 上 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 的线程 Dispatcher 才能访问 DispatcherObject。

任何线程都可以检查它是否有权访问此 DispatcherObject。

和 VerifyAccess 之间的差异CheckAccess是 返回CheckAccess一个布尔值，指定调用线程是否有权访问此 DispatcherObject ，并在VerifyAccess调用线程无权访问此 DispatcherObject时引发异常。

调用此方法与对关联的 Dispatcher 对象调用CheckAccess相同。