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    <p>There are, strictly speaking, no "memory leaks" within the "sandbox" of a managed .NET project; there are only references held longer than the developer would think necessary. Fredrik has the right of it; when you attach a handler to an event, because the handler is usually an instance method (requiring the instance), the instance of the class containing the listener stays in memory as long as this reference is maintained. If the listener instance contains references to other classes in turn (e.g. backreferences to containing objects), the heap can stay quite large long after the listener has gone out of all other scopes.</p> <p>Maybe someone with a bit more esoteric knowledge of Delegate and MulticastDelegate can shed some light on this. The way I see it, a true leak COULD be possible if all of the following were true:</p> <ul> <li>The event listener requires external/unmanaged resources to be released by implementing IDisposable, but it either does not, or</li> <li>The event multicast delegate does NOT call the Dispose() methods from its overridden Finalize() method, and</li> <li>The class containing the event does not call Dispose() on each Target of the delegate through its own IDisposable implementation, or in Finalize().</li> </ul> <p>I've never heard of any best practice involving calling Dispose() on delegate Targets, much less event listeners, so I can only assume the .NET developers knew what they were doing in this case. If this is true, and the MulticastDelegate behind an event tries to properly dispose of listeners, then all that is necessary is proper implementation of IDisposable on a listening class that requires disposal.</p>
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    1. POHow do events cause memory leaks in C# and how do Weak References help mitigate that?
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    1. COMy definition of memory leak would suggest that a program generally has a memory leak iff there exists a repeating sequence of inputs which will cause the program to require an unbounded amount of memory while passing through a bounded number of observable states. By such a definition, events can certainly cause memory leaks even within an entirely-managed .net program. Event listeners should implement `IDisposable`, and should unsubscribe from their events in `Dispose`, but Microsoft does not make it easy to do that consistently, and unfortunately sloppiness doesn't usually cause trouble.
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    2. COThe `MulticastDelegate` does not itself do anything with `IDisposable`; calling `Delegate.Remove` (as event-unsubscribe methods usually do) simply creates a new `MulticastDelegate` which doesn't contain the removed item. Finalizers are generally useless with events, since an event will keep all its subscribers in scope as long as the publisher is in scope. By the time a subscriber could be finalized, the publisher will be out of scope and the event will be irrelevant.
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