RoutedCommands Executed and PreviewExecuted events

Question

My problem is that I would like to handle a commands in multiple places. For instance I have my custom UserControl where a Button is bound to some command. I have a command binding in that control but I also have a command binding in a Window which uses this control.

My aim is to perform some action inside the control while not interrupting handling of the command in the Window.

I tried experimenting with Executed and PreviewExecuted events but with no luck. Then I simulated the problem in a single window (code posted below).

<Window x:Class="CommandingEvents.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:CommandingEvents="clr-namespace:CommandingEvents" 
    Title="Window1" Height="300" Width="300">
<Window.CommandBindings>
    <CommandBinding 
        Command="{x:Static CommandingEvents:Window1.Connect}"
        Executed="CommandBindingWindow_Executed"
        PreviewExecuted="CommandBindingWindow_PreviewExecuted"/>
</Window.CommandBindings>
<Grid>
    <Grid.CommandBindings>
        <CommandBinding 
        Command="{x:Static CommandingEvents:Window1.Connect}"
        Executed="CommandBindingGrid_Executed"
        PreviewExecuted="CommandBindingGrid_PreviewExecuted" />
    </Grid.CommandBindings>
    <Button Command="{x:Static CommandingEvents:Window1.Connect}" 
            CommandTarget="{Binding RelativeSource={RelativeSource Self}}"
            Content="Test" HorizontalAlignment="Center" VerticalAlignment="Center" />
</Grid>

namespace CommandingEvents
{
    public partial class Window1
    {
        public static readonly RoutedUICommand Connect = new
            RoutedUICommand("Connect", "Connect", typeof(Window1));

        public Window1()
        {
            InitializeComponent();
        }

        private void CommandBindingWindow_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            Console.WriteLine("CommandBindingWindow_Executed");
            e.Handled = false;
        }

        private void CommandBindingGrid_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            Console.WriteLine("CommandBindingGrid_Executed");
            e.Handled = false;
        }

        private void CommandBindingWindow_PreviewExecuted(object sender, ExecutedRoutedEventArgs e)
        {
            Console.WriteLine("CommandBindingWindow_PreviewExecuted");
            e.Handled = false;
        }

        private void CommandBindingGrid_PreviewExecuted(object sender, ExecutedRoutedEventArgs e)
        {
            Console.WriteLine("CommandBindingGrid_PreviewExecuted");
            e.Handled = false;
        }
    }
}

When I hit the button only "CommandBindingWindow_PreviewExecuted" is printed out. Why is that? I tried to set e.Handled to false but it doesn't make a difference. Can anyone explain this behaviour?

Answer 1

I have no idea why that happens (and how it isn't a bug) but here is what was written in the WPF wiki:

There is a particularity about CommandBinding which is extremely interesting and important to know.

The CommandManager uses routed events to notify the different CommandBinding objects that a command execution was invoked (through default gestures, input bindings, explicitly, etc.).

Up to now, this is fairly straightforward. However, what is more important is that CommandBinding will mark the routed event from the CommandManager as handled as soon as a handler gets executed (either PreviewExecuted or Executed).

Finally, even if your handler has a prototype that matches a delegate called ExecutedRoutedEventHandler, the Executed event from the CommandBinding is not a RoutedEvent but a normal CLR event. Setting or leaving the e.Handled flag to false will change nothing.

Therefore, as soon as an Executed or PreviewExecuted handler is invoked, the RoutedCommand will halt its routing.