Question

When you are adding and removing event handlers and you want to have additional parameters, how do you go about doing this? The below code is like something i would want but obviously does not work.

How would you go about this? – it’s troublesome that i cant use delegates or lambdas as i need to also remove the handler.

    private static void IsDefaultChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs args)
    {
        if ((bool)args.NewValue)
        {
            Window.Current.CoreWindow.KeyUp += CoreWindowOnKeyUp(dependencyObject);
        }
        else
        {
            Window.Current.CoreWindow.KeyUp -= CoreWindowOnKeyUp(dependencyObject);
        }

    }

    private static void CoreWindowOnKeyUp(CoreWindow sender, KeyEventArgs args, DependencyObject dependencyObject)
    {
        ((ICommand)dependencyObject.GetValue(Button.CommandProperty)).Execute(null);
    }

Answer 1

What you can do is:

• Keep some collection of DependencyObjects that you add to/remove from in your IsDefaultChanged method.
• Modify your CoreWindowOnKeyUp handler so it only accepts the expected two parameters, and queries the collection of DependencyObjects itself. Bind this event once and don’t unbind it.

I.e. rather than having an event with a handler for each current dependency object, you have an event with a single handler that queries a collection for current dependency objects.

HashTable<DependencyObject> current = new HashTable<DependencyObject>();

// Bound as before
private static void IsDefaultChanged(
    DependencyObject dependencyObject,
    DependencyPropertyChangedEventArgs args)
{
    if ((bool)args.NewValue)
        current.Add(dependencyObject);
    else
        current.Remove(dependencyObject);
}

// Permanently bound, once.
private static void CoreWindowOnKeyUp(CoreWindow sender, KeyEventArgs args)
{
    foreach(var do in current)
    {
        ((ICommand)do.GetValue(Button.CommandProperty)).Execute(null);
    }
}

Alternatively, if Richard’s code doesn’t unbind lambdas properly, you can keep a Dictionary<DependencyObject, EventHandler> so you can retrieve the exact lambda that was bound and unbind it accordingly.