Dispatcher.CheckAccess 方法

定義

命名空間:
System.Windows.Threading
組件:
WindowsBase.dll

判斷呼叫執行緒是否即為與此 Dispatcher執行緒相關聯的執行緒。

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

傳回

Boolean

true 若呼叫執行緒是與此 Dispatcher關聯的執行緒;否則， false。

範例

以下範例用 CheckAccess 來判斷執行緒是否能存取 Button。 CheckAccess與 相關的 Dispatcher 方法Button被呼叫以驗證對執行緒的存取。 若呼叫執行緒能存取 Dispatcher， Button 則透過存取 的成員 Button進行更新;否則，接受 參數 Button 的代理將被置於 Dispatcher。 他們 Dispatcher 將委派更新 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

備註

只有 a Dispatcher 所建立的 該DispatcherObject物件才能存取該物件。 使用 Invoke 或 BeginInvoke 從不同執行緒存取該物件。

CheckAccess 可以從任何執行緒呼叫。

與 CheckAccessVerifyAccess 之間的差異CheckAccess會回傳一個布林值，表示呼叫執行緒是否有權限存取 並DispatcherVerifyAccess拋出例外。

適用於

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