ios - didReceiveMemoryWarning，viewDidUnload

Question

我在读一本书，它建议将我的 IBOutlets 声明为 weak 应该可以解决当我的应用程序收到内存不足警告时的问题。例如，我现在不再需要在 viewDidUnload 方法中将这些 socket 设置为 nil。

我还听说在 iOS6 中 viewDidUnload 被弃用，取而代之的是 didReceiveMemoryWarning 被调用。

无论如何，我该如何继续，我是否应该将我的 IBOutlet 声明为 weak，并“忘记”实现 didReceiveMemoryWarnings 和 viewDidUnloads?

Answer 1

不是所有的 IBOutlets 都应该是 weak。来自Apple docs (Resource Programming guide)的推荐

Outlets should generally be weak, except for those from File’s Owner to top-level objects in a nib file (or, in iOS, a storyboard scene) which should be strong. Outlets that you create should therefore typically be weak, because:

• Outlets that you create to, for example, subviews of a view controller’s view or a window controller’s window, are arbitrary references between objects that do not imply ownership.

• The strong outlets are frequently specified by framework classes (for example, UIViewController’s view outlet, or NSWindowController’s window outlet).

例子:

XIB 中的顶级对象应声明为strong，任何其他 subview /控件应为weak 属性。

    @property (nonatomic, weak)   IBOutlet MyView *viewContainerSubview;
    @property (nonatomic, strong) IBOutlet MyOtherClass *topLevelObj;

使用 ARC weak 生命周期限定符有其自身的优势(Refer Apple docs)因为，

__weak specifies a reference that does not keep the referenced object alive. A weak reference is set to nil when there are no strong references to the object.

因此您不必担心设置 IBOutlets nil，它的生命周期自动受其顶级实例的约束。

应实现

didReceiveMemoryWarning 以清除任何占用内存的可重新创建资源。当您收到 didReceiveMemoryWarning 调用时，它应该用于释放使用的非关键资源，例如:自定义数据结构、用于填充 UI 的网络服务响应等。任何资源需求的非关键性由开发者决定。