Dispatcher.CheckAccess メソッド

定義

呼び出し元のスレッドがこの Dispatcher に関連付けられたスレッドであるかどうかを判断します。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

戻り値

呼び出し元のスレッドがこの Dispatcher に関連付けられたスレッドである場合は true。それ以外の場合は falsetrue if the calling thread is the thread associated with this Dispatcher; otherwise, false.

次の例でCheckAccessは、を使用して、 Buttonスレッドがにアクセスできるかどうかを判断します。The following example uses CheckAccess to determine whether a thread has access to a Button. に関連付けらDispatcherれているButtonのメソッドを呼び出して、スレッドへのアクセスを確認します。CheckAccessThe CheckAccess method on the Dispatcher associated with the Button is called to verify access to the thread. 呼び出し元のスレッドDispatcherがにアクセスできる場合Button 、はのメンバーにButtonアクセスすることによって更新されます。それ以外Buttonの場合は、を引数としDispatcherて受け取るデリゲートがに配置されます。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. は、のButton更新作業を委任します。 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

注釈

によって作成DispatcherObjectされただけがオブジェクトにアクセスできます。DispatcherOnly the Dispatcher that a DispatcherObject is created on may access the object. InvokeBeginInvokeスレッドからオブジェクトにアクセスするには、またはを使用します。Use Invoke or BeginInvoke to access the object from a different thread.

CheckAccess任意のスレッドから呼び出すことができます。CheckAccess can be called from any thread.

CheckAccess Dispatcher VerifyAccessとの違いはCheckAccess 、呼び出し元のスレッドがにアクセスできるかどうかを示すブール値を返し、例外をスローします。 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.

適用対象

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