ARC委托内存管理 [英] ARC delegate memory management

问题描述

在Apple的文档中，它说

In Apple's docs it says

如果您需要管理除释放实例变量之外的资源，则可以实现dealloc方法。您不必（实际上不能）释放实例变量，但您可能需要在系统类和其他未使用ARC编译的代码中调用[systemClassInstance setDelegate：nil]。

You may implement a dealloc method if you need to manage resources other than releasing instance variables. You do not have to (indeed you cannot) release instance variables, but you may need to invoke [systemClassInstance setDelegate:nil] on system classes and other code that isn’t compiled using ARC.

这是否包括UIKit和Framework委托，例如， UIPageViewController 的父代有委托 UIPageViewControllerDelegate - 这必须在dealloc中填充吗？

Does this include UIKit and Framework delegates, for example, the parent of a UIPageViewController has the delegate UIPageViewControllerDelegate - does this have to be nilled in the dealloc?

推荐答案

当你有一个关系在父控制器及其视图之间，父控制器作为视图委托，其中一个关系不能保留另一个，否则将有一个保留周期和内存泄漏。

When you have a relationship between the a parent controller and its view, where the parent controller acts as the views delegate, one of those relationships must not retain the other, otherwise you will have a retain cycle and a memory leak.

有两种方法可以执行此操作：

• 首先是将委托标记为__unsafe_unretained。如果这样做，您将需要在控制器的dealloc中手动删除引用。

• There first is to mark the delegate as __unsafe_unretained. If you do this you will need to manually nil out the reference in the dealloc of the controller.

第二个是使用弱引用。大多数ARC发生在编译时。这有助于通过减少垃圾收集器会发生的CPU周期来节省电池消耗。然而，对于弱引用，有一个运行时过程来维护这些变量的映射，观察它们，并根据需要对它们进行排序。这就是为什么弱引用需要iOS5.1 - 它不仅仅是一个编译器功能。

The second is to use a weak reference. Most of ARC happens at compile time. This helps to save battery drain by reducing the CPU cycles that would otherwise occur with a garbage collector. However, for weak references, there's a run-time process that maintains a map of these variables, observes them, and nils them out as required. This is why weak references required iOS5.1 - its not just a compiler feature.

如果使用太多的弱引用，它可能是一个性能开销。在实践中，这几乎不会成为一个问题。

If you use too many weak references, it can be a performance overhead. In practice this will hardly ever be a concern.

摘要

• 如果使用弱引用，则不需要手动将其删除。检查你没有内存，通过一个强有力的引用的保留周期。


• 如果你真的必须使用__unsafe_unretained（也就是'assign'）。


• 同样的规则适用于UIKit和框架类。好的是，它们非常一致。

更新

纠正我的诡计评论：如果您的代表在控制器执行之前移除，那么您将需要手动将其关闭控制器 - 谢谢@borrden。

• Correcting my dodgy comment: If your delegate goes away before the controller does, then you will need to nil it off the controller manually - thanks @borrden.

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