How to add additional actions to command

Question

I am inheriting from a window control that already handles the ApplicationCommands.Close command so that it handles closing the window natively.

I would like to add/override the existing functionality, however I cannot seem to figure out how to do this.

Tried:

• Adding another of the same command to CommandBindings (first declared seems to win)
• Check if the command is already existing...Cannot seem to find a way to do this

Answer 1

There are a couple of things you can try. If you are just trying to prevent your window from closing, you can override the OnClosing method and set the cancelled flag:

protected override void OnClosing(CancelEventArgs e)
{
    e.Cancel = true;
    base.OnClosing(e);
}

If you want to specifically alter the behavior, you can register with preview versions of the command:

<Window.CommandBindings>
    <CommandBinding Command="ApplicationCommands.Close"
                    PreviewExecuted="CloseCommandHandler"
                    PreviewCanExecute="CanExecuteHandler" />
</Window.CommandBindings>

The preview routed events will happen before the standard events, allowing you to handle the logic before your base class.

Answer 2

If you want to replace functionality of the global command, you can find the specific command binding, remove it then add your own logic. See below.

    public ChildWindow()
        :base()
    {
        var appCloseCommandBinding =
            CommandBindings.Cast<CommandBinding>().SingleOrDefault(item => item.Command == ApplicationCommands.Close);

        if(appCloseCommandBinding != null)
            CommandBindings.Remove(appCloseCommandBinding);

        CommandBindings.Add(new CommandBinding(ApplicationCommands.Close, YourCommandLogic));
    }

Hope it can help.