在什么情况下脱离事件是必要的? [英] In what cases are detaching from events necessary?

问题描述

我不确定我是否完全清楚附加到对象中的事件的含义.

I'm not sure if I'm entirely clear on the implications of attaching to events in objects.

这是我目前的理解，正确或详细:

This is my current understanding, correct or elaborate:

1.附加到本地类事件不需要分离

例子:

this.Closing += new System.ComponentModel.CancelEventHandler(MainWindow_Closing);

公共事件 EventHandler OnMyCustomEvent = delegate { };

我假设当你的对象被释放或垃圾回收时，函数被释放并自动从事件中分离.

I'm assuming that when your object is disposed or garbage collected, the functions are deallocated and would automatically detach from the events.

<强>2.附加到您不再需要的对象 (= null;) 必须从中分离

示例:附加到计时器的 Elapsed 事件，您只响应一次.我假设您需要将 Timer 存储在局部变量中，以便在事件触发后分离 Elapsed 事件.因此，像这样在本地方法范围内声明计时器会导致泄漏:

Examples: Attaching to a timer's Elapsed event, which you only respond to once. I would assume you need to store the Timer in a local variable so you can detached the Elapsed event after the event fires. Thus, declaring the timer in a local method scope like so would result in a leak:

System.Timers.Timer myDataTimer = new System.Timers.Timer(1000);myDataTimer.Elapsed += new System.Timers.ElapsedEventHandler(myDataTimer_Elapsed);

3.将本地对象中的事件附加到您的类不需要处置?

例如，如果您有一个 ObservableCollection，您可以创建、监控并让它消失.如果您使用本地私有函数附加到 CollectionChanged 事件，当您的类被垃圾回收时，该函数不会释放，导致 ObservableCollection 也被释放吗?

For example, if you had an ObservableCollection that your creates, monitors, and lets die. If you attached to the CollectionChanged event using a local, private function, wouldn't this function deallocate when your class is garbage collected, causing the ObservableCollection to also be freed?

我确定在某些地方我已经停止使用对象并且未能从事件中分离(例如，我制作的计时器示例)，因此我正在寻找有关其工作原理的更清晰的解释.

I'm sure I have places where I've stopped using objects and have failed to detach from an event (for example, the timer example I made), so I'm looking for a clearer explanation on how this works.

推荐答案

我认为你让它变得比它需要的更复杂.你只需要记住两件事:

I think you're making it more complicated than it needs to be. You just need to remember two things:

• 当您订阅某个事件时，该事件的所有者"(发布者)通常会保留对您订阅的委托的引用.
• 如果您使用实例方法作为委托的操作，则委托具有对其目标"对象的引用.

这意味着如果你写:

publisher.SomeEvent += subscriber.SomeMethod;

那么在 publisher 之前，subscriber 将没有资格进行垃圾回收，除非您稍后取消订阅.

Then subscriber won't be eligible for garbage collection before publisher is unless you unsubscribe later.

请注意，在许多情况下，subscriber 只是 this:

Note that in many cases, subscriber is just this:

publisher.SomeEvent += myDataTimer_Elapsed;

相当于:

publisher.SomeEvent += this.myDataTimer_Elapsed;

假设它是一个实例方法.

assuming it's an instance method.

没有由于事件订阅的反向关系 - 换句话说，订阅者不会让发布者保持活动状态.

There is no reverse relationship just due to event subscription - in other words the subscriber doesn't keep the publisher alive.

顺便说一下，有关更多信息，请参阅 我关于事件和代表的文章.

See my article on events and delegates for more information, by the way.

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