ARC捕获self ...阻塞块内部并在执行之前释放引用 [英] ARC capturing self... block inside a block and reference being released before execution

问题描述

我有这个问题：一个块里面的一个块。

I have this problem: a block inside a block.

  self.createStuff = ^ (NSString *text) {       
        self.post.onCompletion = ^(NSURLResponse *response, NSData *data, NSError *error){
                [self doStuff];  // error here
        };
        [self doMoreStuff];  // error here
  };

我将在[self doStuff]和[self doMoreStuff]中出错。错误在此区块中强烈捕获自我可能会导致保留周期

I will have errors in [self doStuff] and on [self doMoreStuff]. The error is capturing 'self' strongly in this block is likely to lead to a retain cycle

很容易说，只需添加

id mySelf = self; 

在第一个块之前并改为使用mySelf。

before the first block and use mySelf instead.

不。这不会保存我的问题，只是因为我自己是一个善意的id不会给我一个post属性，第二行需要。所以我需要声明它像

Nope. This will not save my problem, simply because mySelf being of kind id will not give me a post property, needed by the second line. So I need to declare it like

MyClass *mySelf = self;

如下所示：

MyClass *mySelf = self;

  self.createStuff = ^ (NSString *text) {       
        mySelf.post.onCompletion = ^(NSURLResponse *response, NSData *data, NSError *error){
                [self doStuff];  // error here
        };
        [mySelf doMoreStuff];  
  };

好吧，你说，现在self.post.onCompletion行和doMoreStuff不再抱怨了，但是我们在onCompletion中有另一个self ...因为这是一个块内的块。我可以重复创建另一个弱引用的过程，这将是弱引用的弱引用

OK, you say, now the self.post.onCompletion line and doMoreStuff are not complaining anymore, but we have another self inside onCompletion... because this is a block inside a block. I can repeat the process creating another weak reference like and this will have to be a weak reference to a weak reference

MyClass *internalMyself = mySelf;

并使用

   [internalMyself doStuff];

在我看来这是一个非常可怜的方式来做这个以及更多，应用程序挂起时，这个方法运行。在方法执行之前，类似于引用的东西被释放...

this seems to me to be a pretty pathetic way to do this and more, the app hangs when this method runs. Something like the reference is being deallocated before the method executes...

如何解决这个问题？

谢谢。

注意：这是编译到iOS 6 +

note: this is being compiled to iOS 6+

推荐答案

你非常接近。只需更换您的解决方案

You're pretty close. Just replace your solution

MyClass *mySelf = self;

self.createStuff = ^ (NSString *text) {       
     mySelf.post.onCompletion = ^(NSURLResponse *response, NSData *data, NSError *error) {
          [self doStuff];  // error here
     };
     [mySelf doMoreStuff];  
};

with

__weak MyClass *mySelf = self;

self.createStuff = ^ (NSString *text) {       
     mySelf.post.onCompletion = ^(NSURLResponse *response, NSData *data, NSError *error) {
          [self doStuff];  // error here
     };
     [mySelf doMoreStuff];  
};

第一个解决方案的问题是 mySelf 未指定弱，因此所有权限定符隐式 __ strong （请参阅LLVM的文档）。我不确定为什么这会在第一个块中消除警告，但是指定引用 __ weak 将完全删除保留周期。

The problem with the first solution is that mySelf isn't designated weak, so it's ownership qualifier is implicitly __strong (see LLVM's documentation). I'm not sure why this quiets the warning in the first block, but designating the reference __weak will fully remove the retain cycle.

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