DispatcherObject.CheckAccess Método

Definição

Determina se o thread de chamada tem acesso a este DispatcherObject.Determines 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

Retornos

Boolean

true se o thread de chamada tiver acesso a esse objeto; caso contrário, false.true if the calling thread has access to this object; otherwise, false.

Exemplos

O exemplo a seguir usa CheckAccess para determinar se um thread tem acesso ao thread em que um Button foi criado.The following example uses CheckAccess to determine whether a thread has access to the thread that a Button was created on. O método CheckAccess na Button é chamado para verificar o acesso ao thread.The CheckAccess method on the Button is called to verify access to the thread. Se o thread de chamada tiver acesso, o Button será atualizado acessando apenas os membros da Button; caso contrário, um delegado, que aceita um Button como argumento, é Postado na Dispatcher do Button.If 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

Comentários

Somente o thread no qual o Dispatcher foi criado pode acessar o DispatcherObject.Only the thread the Dispatcher was created on may access the DispatcherObject.

Qualquer thread pode verificar se ele tem acesso a esse DispatcherObject.Any thread can check to see whether it has access to this DispatcherObject.

A diferença entre CheckAccess e VerifyAccess é que CheckAccess retorna um booliano que especifica se o thread de chamada tem acesso a esse DispatcherObject e VerifyAccess gera uma exceção se o thread de chamada não tem acesso a esse DispatcherObject.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.

Chamar esse método é idêntico a chamar CheckAccess no objeto Dispatcher associado.Calling this method is identical to calling CheckAccess on the associated Dispatcher object.

Aplica-se a