Dispatcher.CheckAccess 方法

定義

判斷呼叫的執行緒是否為與這個 Dispatcher 關聯的執行緒。Determines whether the calling thread is the thread associated with this Dispatcher.

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

傳回

如果呼叫的執行緒為與這個 Dispatcher 關聯的執行緒則為 true,否則為 falsetrue if the calling thread is the thread associated with this Dispatcher; otherwise, false.

範例

下列範例會使用CheckAccess來判斷線程是否Button可存取。The following example uses CheckAccess to determine whether a thread has access to a Button. 會呼叫與Dispatcher CheckAccess相關聯之上的方法,以驗證執行緒的存取權。 ButtonThe CheckAccess method on the Dispatcher associated with the Button is called to verify access to the thread. 如果呼叫Dispatcher的執行緒具有的存取權Button ,就會藉由Button存取的成員來更新, Button否則會將接受做為引數的委派放在Dispatcher上。If the calling thread has access to the Dispatcher, the Button is updated by accessing the members of the Button; otherwise, a delegate, which accepts a Button as an argument, is placed onto the Dispatcher. 會委派更新的Button工作。 DispatcherThe Dispatcher will delegate the work of updating the 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

Dispatcher 只有在上建立的DispatcherObject才可存取物件。Only the Dispatcher that a DispatcherObject is created on may access the object. 使用InvokeBeginInvoke從不同的執行緒存取物件。Use Invoke or BeginInvoke to access the object from a different thread.

CheckAccess可以從任何執行緒呼叫。CheckAccess can be called from any thread.

CheckAccess CheckAccess Dispatcher之間的差異會傳回布林值,指出呼叫執行緒是否具有的存取權, VerifyAccess並擲回例外狀況。 VerifyAccessThe difference between CheckAccess and VerifyAccess is CheckAccess returns a Boolean indicating whether the calling thread has access to the Dispatcher and VerifyAccess throws an exception.

適用於

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