Creating a weak event

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Introduction

This simple article shows that creating a weak event (an event that allows objects who respond to it to be collected) is really simple with the help of the WeakDelegateSet class.

Background

I created this class when I discovered a stupid bug (but, one that can turn to be a serious problem) in my other article. Classes that registered themselves in GCUtils.Collected where not allowed to be collected themselves if they didn't unregister from the event. It must be a weak event, so I did it, and created a class that helps this process.

Using the code

To create a weak event, you must create a WeakDelegateSet, and must redirect the add and remove handlers of the event to that WeakDelegateSet. For example:

private WeakDelegateSet fMyWeakEvent = new WeakDelegateSet();
public event EventHandler MyWeakEvent
{
    add
    {
        fMyWeakEvent.Add(value);
    }
    remove
    {
        fMyWeakEvent.Remove(value);
    }
}

And then, you invoke the event using the Invoke method in the WeakDelegateSet, passing all the required parameters to it. So, for my example event:

fMyWeakEvent.Invoke(this, EventArgs.Empty);

This is all that is needed to create a weak event. Maybe this is not a very common requirement, but I needed the weak event to be able to collect objects that were registered for the Collected event in case Dispose was not invoked. And, I am sure many events may use this as many times we need to be informed of something when the object is really alive.

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)