Will Event Handlers Prevent Garbage Collection of My Objects?

Do event handlers interfere with garbage collection?

Question:

Consider the following code:

<code class="language-c#">MyClass pClass = new MyClass();
pClass.MyEvent += MyFunction;
pClass = null;</code>

Will pClass be garbage collected? Or will it persist and continue to trigger events? Do you need to unsubscribe from events like this:

<code class="language-c#">MyClass pClass = new MyClass();
pClass.MyEvent += MyFunction;
pClass.MyEvent -= MyFunction;
pClass = null;</code>

Answer:

Garbage collection by event publisher:

Subscription to MyEvent does not affect the garbage collection of pClass (publisher).

Garbage collection of target object:

Generally, garbage collection behavior depends on whether MyFunction is an instance method or a static method:

• Instance methods: Subscribing MyFunction to MyEvent includes a reference to MyClass. Therefore, it may prevent garbage collection of the target object. However, this problem stops once the publisher object becomes eligible for collection.
• Static methods: Static events do not prevent the target object from being garbage collected.

Other notes:

• If the publisher (e.g., pClass) is long-lived and outlives the target object (e.g., the object containing MyFunction), you need to unsubscribe to ensure that the target object can be garbage collected.
• Static events are especially dangerous when used in conjunction with instance-based handlers, as they may prevent garbage collection of the target object indefinitely.

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