PreviewCanExecuteEvent not executed

Question

Hi folks

I have a problem with my WPF program. I'm trying to create an object that will add handlers to all controls in the same scope.

The following line does not work. The event is not handled.

element.AddHandler(CommandManager.PreviewCanExecuteEvent, new CanExecuteRoutedEventHandler(scope.CanExecutedHandler), true);

I also have a Command binded to the button. So the idea is that i want CanExecute of the Command to run: This works fine. I also want a handler for the PreviewCanExecute: This does not work.

I'm sorry that I can not explain any better.

See my code below:

XAML:

<Window.Resources>
    <my:PermissionScope x:Key="permissionManager"/>
</Window.Resources>
<StackPanel>
    <TextBox Height="23" Name="textBox1" Width="120" />
    <Button Content="Permission Required" Command="{Binding Path=PermissionRequired}" my:PermissionScope.SharedPermissionScope="{StaticResource permissionManager}"/>
    <Button Content="Permission not required" Command="{Binding Path=PermissionRequired}"/>
</StackPanel>

PermissionScope.cs

public class PermissionScope
{

    public static readonly DependencyProperty SharedPermissionScopeProperty =
        DependencyProperty.RegisterAttached("SharedPermissionScope", typeof(PermissionScope), typeof(PermissionScope),
        new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.Inherits,
        new PropertyChangedCallback(OnUseGlobalSharedPermissionScopeChanged)));

    public static void SetSharedPermissionScope(DependencyObject depObj, PermissionScope scope)
    {
        // never place logic in here, because these methods are not called when things are done in XAML
        depObj.SetValue(SharedPermissionScopeProperty, scope);
    }

    public static PermissionScope GetSharedPermissionScope(DependencyObject depObj)
    {
        // never place logic in here, because these methods are not called when things are done in XAML
        return depObj.GetValue(SharedPermissionScopeProperty) as PermissionScope;
    }

    private static void OnUseGlobalSharedPermissionScopeChanged(DependencyObject depObj, DependencyPropertyChangedEventArgs args)
    {
        if (depObj is Button)
        {
            if (args.OldValue != null)
            {
                RemoveEventHandlers(depObj as UIElement, args.OldValue as PermissionScope);
            }
            if (args.NewValue != null)
            {
                AttachEventHandlers(depObj as UIElement, args.NewValue as PermissionScope);
            }
        }
    }

    private static void AttachEventHandlers(UIElement element, PermissionScope scope)
    {
        if (element != null && scope != null)
        {
            element.AddHandler(CommandManager.PreviewCanExecuteEvent, new CanExecuteRoutedEventHandler(scope.CanExecutedHandler), true); // we need to see all events to subvert the built-in undo/redo tracking in the text boxes
        }
    }

    private static void RemoveEventHandlers(UIElement element, PermissionScope scope)
    {
        if (element != null && scope != null)
        {
            element.AddHandler(CommandManager.PreviewCanExecuteEvent, new CanExecuteRoutedEventHandler(scope.CanExecutedHandler));
        }
    }

    private void CanExecutedHandler(object sender, CanExecuteRoutedEventArgs e)
    {
        if (e.Command is CommandBase)
        {
            bool hasPermission = false;
            hasPermission = ((CommandBase)e.Command).HasPermission();

            ShowControl((UIElement)e.OriginalSource, hasPermission);
        }
    }

    public static void ShowControl(UIElement element, bool show)
    {
        element.Visibility = show ? Visibility.Visible : Visibility.Collapsed;
    }
}

I really not some help.

Best regards, Michael

Answer 1

I found out my self. This will only work with RoutedCommands and not ICommand