保留使用addObserverForName：object：queue：usingBlock： [英] Retain cycles when using addObserverForName:object:queue:usingBlock:

问题描述

我是使用block编程的新手。我在我的Listener类中有以下代码（不使用弧）：

I am new to programming with block. I have following code (not using arc) in my Listener class:

- (void)someBlock:((void)^(NSDictionary *)myDictionary)myBlock
{
    __block Listener *weakSelf = self;
    weakSelf = [[NSNotificationCenter defaultCenter] 
                   addObserverForName:@"MyNotification"
                               object:nil
                                queue:nil
                           usingBlock:^(NSNotification *note) 
        { 
            //--- Here have the retain cycles
            myBlock(note.userInfo);
            [[NSNotificationCenter defaultCenter] removeObserver:weakSelf
                                                            name:@"MyNotification"];
        }];
}

和在我的DoMyStuff类中：

and in my DoMyStuff class:

... some code
Listener *myListener = [[[Listener alloc] init] autorelease];
[myListener someBlock:((void)^(NSDictionary *)myDictionary)myBlock{
    [self.someProperty doSomething:myDictionary];
}];

任何人都能告诉我解决保留周期的正确方向？
我已检查过这两个问题。

Can anyone tell me the right direction to solve the retain cycles? I have checked these two questions

1. 正确管理addObserverForName：object：queue：usingBlock：


2. 为什么不从NSNotificationCenter中删除Observer：addObserverForName：usingBlock get called

1. "Correct management of addObserverForName:object:queue:usingBlock:"
2. "Why doesn't Remove Observer from NSNotificationCenter:addObserverForName:usingBlock get called"

但是他们没有在另一个块中使用块，所以，这里的解决方案不适合我。

but they did not use block inside another block, so, the solutions there don't work for me.

推荐答案

这里的问题是你使用 [self.someProperty doSomething：myDictionary]; 请注意，使用ivars将导致保留周期，因为它与自身> ivar相同。

The problem here is that you are using [self.someProperty doSomething:myDictionary]; inside block thus retaining self. Note that using ivars will lead to retain cycles as it's the same as self->ivar.

通常它看起来像这样（__weak / __ unsafe_unretained用于ARC，__block用于MRR ）

Usually it looks like this (__weak/__unsafe_unretained is for ARC, __block for MRR)

__weak ClassName *weakSelf = self;
[SomeClass someMethodWithBlock:^{
    // use weakSelf here; if you want to make sure that self is alive throughout whole block, do something like ClassName *strongSelf = weakSelf;
}];

有很好的库 https://github.com/jspahrsummers/libextobjc ，其中包含@ weakify / @ strongify宏（可能仅限于ARC）。

There is nice library https://github.com/jspahrsummers/libextobjc which has @weakify/@strongify macroses for this(probably ARC only).

如果可能的话，你应该使用ARC（它可以从iOS 4，如果我记得正确，从__weak从iOS 5，这应该很好这些天）。

Also you should use ARC if possible(it is available from iOS 4, if I remember correctly and has __weak from iOS 5, which should be fine these days).

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