CommandManager.AddPreviewCanExecuteHandler 方法

定義

命名空間:
System.Windows.Input
組件:
PresentationCore.dll

將指定 CanExecuteRoutedEventHandler 元素附加到指定元素上。

public:
 static void AddPreviewCanExecuteHandler(System::Windows::UIElement ^ element, System::Windows::Input::CanExecuteRoutedEventHandler ^ handler);
public static void AddPreviewCanExecuteHandler(System.Windows.UIElement element, System.Windows.Input.CanExecuteRoutedEventHandler handler);
static member AddPreviewCanExecuteHandler : System.Windows.UIElement * System.Windows.Input.CanExecuteRoutedEventHandler -> unit
Public Shared Sub AddPreviewCanExecuteHandler (element As UIElement, handler As CanExecuteRoutedEventHandler)

參數

element
UIElement

該 handler 依靠的元素。

handler
CanExecuteRoutedEventHandler

可以執行處理器。

例外狀況

ArgumentNullException

element 或 handler 為 null。

範例

以下範例會產生 a CanExecuteRoutedEventHandler 和 an ExecutedRoutedEventHandler ，並將其附加到 a，a Button 是該指令的指令來源 Help 。

首先，建立 並 Button 與 Help 指令相關聯。

<Button Command="ApplicationCommands.Help"
        Name="helpButton">Help</Button>

接著，創造 和 CanExecuteRoutedEventHandler 。ExecutedRoutedEventHandler

private void HelpCmdExecuted(object sender, ExecutedRoutedEventArgs e)
{
    // OpenHelpFile opens the help file
    OpenHelpFile();
}

Private Sub HelpCmdExecuted(ByVal sender As Object, ByVal e As ExecutedRoutedEventArgs)
    ' OpenHelpFile opens the help file
    OpenHelpFile()
End Sub

private void HelpCmdCanExecute(object sender, CanExecuteRoutedEventArgs e)
{
    // HelpFilesExists() determines if the help file exists
    if (HelpFileExists())
    {
        e.CanExecute = true;
    }
    else
    {
        e.CanExecute = false;
    }
}

Private Sub HelpCmdCanExecute(ByVal sender As Object, ByVal e As CanExecuteRoutedEventArgs)
    ' HelpFilesExists() determines if the help file exists
    If HelpFileExists() = True Then
        e.CanExecute = True
    Else
        e.CanExecute = False
    End If
End Sub

最後，處理器會使用 AddCanExecuteHandler 和 AddExecutedHandler附加到 Button 。

CommandManager.AddExecutedHandler(helpButton, HelpCmdExecuted);
CommandManager.AddCanExecuteHandler(helpButton, HelpCmdCanExecute);

CommandManager.AddExecutedHandler(helpButton, AddressOf HelpCmdExecuted)
CommandManager.AddCanExecuteHandler(helpButton, AddressOf HelpCmdCanExecute)

適用於

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