Clear All Events Listeners of an Instance or Static Event

Introduction

We had the need to cleanup a WPF Visual tree on windows closing. To do that, we developed a WPF Behavior on the Window component.

On closing, this behavior just ran across the visual tree of the window. Take each component and to this:

• Clear all bindings
• Clear all event listeners (static or not)
• Set the dataContext to null

This helps the GC to collect speedily...

Using the Code

The code to do the clear events part is the following:

public static void ClearEvents(object instance)
{
    var eventsToClear = instance.GetType().GetEvents(
        BindingFlags.Public | BindingFlags.NonPublic
        | BindingFlags.Instance | BindingFlags.Static);

    foreach (var eventInfo in eventsToClear)
    {
        var fieldInfo = instance.GetType().GetField(
            eventInfo.Name, 
            BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Instance);
            
        if (fieldInfo.GetValue(instance) is Delegate eventHandler)
            foreach (var invocatedDelegate in eventHandler.GetInvocationList())
                eventInfo.GetRemoveMethod(fieldInfo.IsPrivate).Invoke(
                    instance, 
                    new object[] { invocatedDelegate });
    }
}

Points of Interest

Reflection is a very powerful tool, but this must not be the main way. This must only be used in critical scenarios.

Be careful of that!

History

• 29^th September, 2021: Version 1