xcode ARC 中的保留循环
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Retain Cycle in ARC
提问by Raj
I have never worked on non ARC based project. I just came across a zombie on my ARC based project. I found it was because of retain cycle.I am just wondering what is a retain cycle.Can
我从未从事过非基于 ARC 的项目。我刚刚在我的基于 ARC 的项目中遇到了一个僵尸。我发现这是因为保留周期。我只是想知道什么是保留周期。可以
Could you give me an example for retain cycle?
你能给我一个保留周期的例子吗？
回答by dasblinkenlight
A retain cycle is a situation when object Aretains object B, and object Bretains object Aat the same time*. Here is an example:
保留周期是对象A保留对象B，对象同时B保留对象A的情况*。下面是一个例子：
@class Child;
@interface Parent : NSObject {
Child *child; // Instance variables are implicitly __strong
}
@end
@interface Child : NSObject {
Parent *parent;
}
@end
You can fix a retain cycle in ARC by using __weakvariables or weakproperties for your "back links", i.e. links to direct or indirect parents in an object hierarchy:
您可以通过为“反向链接”使用__weak变量或weak属性来修复 ARC 中的保留循环，即链接到对象层次结构中的直接或间接父级：
@class Child;
@interface Parent : NSObject {
Child *child;
}
@end
@interface Child : NSObject {
__weak Parent *parent;
}
@end
**这是最原始的保留循环形式；可能有一长串对象将彼此保留在一个圆圈中。
回答by Simon Germain
Here's what a retain cycle is: When 2 objects keep a reference to each other and are retained, it creates a retain cycle since both objects try to retain each other, making it impossible to release.
这是什么是保留循环：当两个对象保持对彼此的引用并被保留时，它会创建一个保留循环，因为两个对象都试图相互保留，从而无法释放。
@class classB;
@interface classA
@property (nonatomic, strong) classB *b;
@end
@class classA;
@interface classB
@property (nonatomic, strong) classA *a;
@end
To avoid retain cycles with ARC, simply declare one of them with a weakreference, like so:
为避免使用 ARC 保留循环，只需使用weak引用声明其中之一，如下所示：
@property (nonatomic, weak) classA *a;
回答by Nick McConnell
This is swift, but here's an interactive demo of retain cycles in iOS: https://github.com/nickm01/RetainCycleLoggerExample
这很快，但这里是 iOS 中保留周期的交互式演示：https: //github.com/nickm01/RetainCycleLoggerExample
