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So, in fact now the Log class knows about the instance of the class that just subscribed to it and holds a reference to it (how else can it deliver the event, if it doesn’t know the address). Thus, the classes that subscribe to the Log and that do no unsubscribe will never be collected by the garbage collection.

I truly hope you understand the issue. If not, I recommend to read this excellent article, it dives into the issue a bit better.

Open instance delegates

The key feature behind this implementation of the weak event pattern is open instance delegates. You are probably wondering: what the hell are open instance delegates? Well, good question, and I will try to explain it. An open instance delegate is just as a regular delegate, it points to the method of a specific class, but the biggest difference is that it does not bind to a specific instance. This means that it can be described as: I know you live on that street (method), but I have not clue in which city (instance) that is. The instance can be specified later. The delegate for a regular event handler looks like this:

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