在MonoBehaviour中注销事件处理程序

Question

I register an event handler (delegate) in the Start method within a class inherited from MonoBehaviour . I want to prevent memory leaks in this case.

public class CharactersController: MonoBehaviour
{
    void Start()
    {
        npc.CollisionEntered += OnNpcCollisionEnter;
    }
}

What is correct or the best method to unregister the delegate? There is a method OnDestroy http://docs.unity3d.com/ScriptReference/MonoBehaviour.OnDestroy.html

The doc says that

This function is called when the MonoBehaviour will be destroyed.

OnDestroy will only be called on game objects that have previously been active.

But it's not clear when MonoBehaviour will be destroyed and what if a gameobject hasn't been activated previously.

Answer 1

在OnEnable中注册事件，然后在OnDisable中注销事件是适当的。

Answer 2

Start() method will not get called unless the behavior is enabled . And it can only be enabled if the game object that it's on is activated. So, you can safely assume that if the behavior gets OnDestroy() called, it did get a call to Start() earlier.

The destruction of mono behaviour happens within the same frame (before rendering) . However, if you are not just asking this because of precaution for memory leaks, but your logic depends on that, something is definitely wrong with it.

As @Programmer correctly noted, your code, most likely, should subscribe and unsubscribe to events in OnEnabled and OnDisabled instead. This follows the concept of component design pattern much better: after all, this pattern assumes (and quite logically so) that components only do their work when deliberately activated by outside systems, and go back to sleep when deactivated. Now, Unity developers have to bend these guidelines a little in a lot of places, because MonoBehaviours are almost the only point of entry they have in terms of C# code, but still, it's better to follow the implicit rules of the system.

And finally, I honestly never saw considerable performance problems in a Unity project because of memory leaks. It is a good that you thinking about it, but your time would be considerably better spent if you eliminated instantiation and destruction of the objects altogether, by moving them to use an object pool , as they are much more often tend to be a source of problems.

Answer 3

If you are only registering the one handler on Start and your CharactersController lasts the lifetime of the application then you aren't going to be leaking memory. It would be more likely to leak if you were registering the handler at some recurring event in the object's lifetime, and then not unregistering it later.