CommandManager.InvalidateRequerySuggested 方法

public:
 static void InvalidateRequerySuggested();

public static void InvalidateRequerySuggested();

static member InvalidateRequerySuggested : unit -> unit

Public Shared Sub InvalidateRequerySuggested ()

示例

以下示例使用 a DispatcherTimer 定期调用 InvalidateRequerySuggested 来强制 CommandManager 引发 RequerySuggested 事件。

//  System.Windows.Threading.DispatcherTimer.Tick handler
//
//  Updates the current seconds display and calls
//  InvalidateRequerySuggested on the CommandManager to force 
//  the Command to raise the CanExecuteChanged event.
private void dispatcherTimer_Tick(object sender, EventArgs e)
{
    // Updating the Label which displays the current second
    lblSeconds.Content = DateTime.Now.Second;

    // Forcing the CommandManager to raise the RequerySuggested event
    CommandManager.InvalidateRequerySuggested();
}

'  System.Windows.Threading.DispatcherTimer.Tick handler
'
'  Updates the current seconds display and calls
'  InvalidateRequerySuggested on the CommandManager to force 
'  the Command to raise the CanExecuteChanged event.
Private Sub dispatcherTimer_Tick(ByVal sender As Object, ByVal e As EventArgs)
    ' Updating the Label which displays the current second
    lblSeconds.Content = Date.Now.Second

    ' Forcing the CommandManager to raise the RequerySuggested event
    CommandManager.InvalidateRequerySuggested()
End Sub

注解

CommandManager唯一注意确定命令目标何时发生更改的某些条件，例如键盘焦点的更改。 CommandManager如果条件不足以确定导致命令无法执行的更改，InvalidateRequerySuggested则可以调用它来强制CommandManager引发RequerySuggested事件。