Dispatcher.VerifyAccess 方法

定義

命名空間:

System.Windows.Threading

組件:

WindowsBase.dll

判斷呼叫執行緒是否能存取此 Dispatcher。

public:
 void VerifyAccess();

public void VerifyAccess();

member this.VerifyAccess : unit -> unit

Public Sub VerifyAccess ()

例外狀況

InvalidOperationException

呼叫執行緒無法存取此 Dispatcher。

範例

以下範例用 VerifyAccess 來判斷執行緒是否能存取 a Button 所建立的執行緒。 此方法取一個物件作為參數，並將其鑄造成 Button。 VerifyAccess呼叫 的 DispatcherButton 方法來驗證對執行緒的存取。

如果呼叫執行緒能存取 Dispatcher，則 Button 只需存取 的成員 Button即可更新。

若呼叫執行緒無法存取，則拋出 an InvalidOperationException 執行緒。 此範例捕捉例外，並將接受 a Button 作為參數的代理推入 DispatcherButton的 。 這 Dispatcher 會完成更新 Button.

// Uses the Dispatcher.VerifyAccess method to determine if
// the calling thread has access to the thread the UI object is on.
private void TryToUpdateButtonVerifyAccess(object uiObject)
{
    Button theButton = uiObject as Button;

    if (theButton != null)
    {
        try
        {
            // Check if this thread has access to this object.
            theButton.Dispatcher.VerifyAccess();

            // The thread has access to the object, so update the UI.
            UpdateButtonUI(theButton);
        }

        // Cannot access objects on the thread.
        catch (InvalidOperationException e)
        {
            // Exception Error Message.
            MessageBox.Show("Exception ToString: \n\n" + e.ToString(),
                "Exception Caught! Thrown During AccessVerify().");

            MessageBox.Show("Pushing job onto UI Thread Dispatcher");

            // Placing job onto the Dispatcher of the UI Thread.
            theButton.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
                new UpdateUIDelegate(UpdateButtonUI), theButton);
        }
    }
}

' Uses the Dispatcher.VerifyAccess method to determine if 
' the calling thread has access to the thread the UI object is on.
Private Sub TryToUpdateButtonVerifyAccess(ByVal uiObject As Object)
    Dim theButton As Button = TryCast(uiObject, Button)

    If theButton IsNot Nothing Then
        Try
            ' Check if this thread has access to this object.
            theButton.Dispatcher.VerifyAccess()

            ' The thread has access to the object, so update the UI.
            UpdateButtonUI(theButton)

            ' Cannot access objects on the thread.
        Catch e As InvalidOperationException
            ' Exception Error Message.
            MessageBox.Show("Exception ToString: " & vbLf & vbLf & e.ToString(), "Execption Caught! Thrown During AccessVerify().")

            MessageBox.Show("Pushing job onto UI Thread Dispatcher")

            ' Placing job onto the Dispatcher of the UI Thread.
            theButton.Dispatcher.BeginInvoke(DispatcherPriority.Normal, New UpdateUIDelegate(AddressOf UpdateButtonUI), theButton)
        End Try
    End If
End Sub

備註

只有 所 Dispatcher 建立的執行緒才能存取 Dispatcher。

此方法是公開的;因此，任何執行緒都可以檢查是否能存取 Dispatcher。

若呼叫執行緒無法存取 ，CheckAccess則 與 之間的差異VerifyAccessCheckAccessDispatcher會回傳布林值，並VerifyAccess拋出例外。

另請參閱

• CheckAccess()