Dispatcher.CheckAccess Metodo

Definizione

Determina se il thread chiamante è il thread associato a questo oggetto Dispatcher.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

Restituisce

true se il thread chiamante è il thread associato a Dispatcher, in caso contrario false.true if the calling thread is the thread associated with this Dispatcher; otherwise, false.

Esempi

Nell'esempio seguente viene usato CheckAccess per determinare se un thread ha accesso a una Button.The following example uses CheckAccess to determine whether a thread has access to a Button. Il metodo CheckAccess sul Dispatcher associato al Button viene chiamato per verificare l'accesso al thread.The CheckAccess method on the Dispatcher associated with the Button is called to verify access to the thread. Se il thread chiamante ha accesso alla Dispatcher, il Button viene aggiornato accedendo ai membri del Button; in caso contrario, un delegato, che accetta un Button come argomento, viene inserito nel Dispatcher.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. Il Dispatcher delegherà il lavoro di aggiornamento del Button.The 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

Commenti

Solo il Dispatcher su cui viene creata una DispatcherObject può accedere all'oggetto.Only the Dispatcher that a DispatcherObject is created on may access the object. Utilizzare Invoke o BeginInvoke per accedere all'oggetto da un thread diverso.Use Invoke or BeginInvoke to access the object from a different thread.

CheckAccess possono essere chiamati da qualsiasi thread.CheckAccess can be called from any thread.

La differenza tra CheckAccess e VerifyAccess è CheckAccess restituisce un valore booleano che indica se il thread chiamante ha accesso al Dispatcher e VerifyAccess genera un'eccezione.The 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.

Si applica a

Vedi anche