Creating a weak event

• Download sample - 29.8 KB

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.