DispatcherObject.CheckAccess 方法

定義

判斷呼叫的執行是否可以存取這個 DispatcherObjectDetermines whether the calling thread has access to this DispatcherObject.

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

傳回

如果呼叫的執行緒可以存取這個物件則為 true,否則為 falsetrue if the calling thread has access to this object; otherwise, false.

範例

下列範例會使用 CheckAccess 來判斷線程是否有權存取 Button 建立所在的執行緒。The following example uses CheckAccess to determine whether a thread has access to the thread that a Button was created on. 呼叫 Button 上的 CheckAccess 方法,以驗證對執行緒的存取。The CheckAccess method on the Button is called to verify access to the thread. 如果呼叫的執行緒有存取權,則只需存取 Button的成員,即可更新 Button。否則,會將接受 Button 做為引數的委派張貼到 ButtonDispatcherIf the calling thread has access, the Button is updated by just accessing the members of the Button; otherwise, a delegate, which accepts a Button as an argument, is posted onto the Dispatcher of the 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

備註

只有建立 Dispatcher 的執行緒可以存取 DispatcherObjectOnly the thread the Dispatcher was created on may access the DispatcherObject.

任何執行緒都可以檢查是否有此 DispatcherObject的存取權。Any thread can check to see whether it has access to this DispatcherObject.

CheckAccessVerifyAccess 之間的差異在於 CheckAccess 會傳回布林值,指定呼叫執行緒是否具有此 DispatcherObject 的存取權,而如果呼叫的執行緒沒有這個 VerifyAccess 的存取權,DispatcherObject會擲回例外狀況。The difference between CheckAccess and VerifyAccess is that CheckAccess returns a Boolean that specifies whether the calling thread has access to this DispatcherObject and VerifyAccess throws an exception if the calling thread does not have access to the this DispatcherObject.

呼叫這個方法等同于在相關聯的 Dispatcher 物件上呼叫 CheckAccessCalling this method is identical to calling CheckAccess on the associated Dispatcher object.

適用於