AFNetworking，UITableView和Blocks(AFNetworking, UITableView and Blocks)

AFNetworking，UITableView和Blocks(AFNetworking, UITableView and Blocks)

所以我正在阅读如何在实现API时避免在块中捕获自身？ 关于内存管理如何在完成块中引用self并且让我思考：以下内容是否会导致保留周期？

伪代码：

[AFnetworking requestGet:@"http://www.website.com" completionBlock:(^)(RequestObj* request, NSError* error){ [self.tableView reloadData]; }];

忽略语法问题，self.tableView会导致保留周期吗？ 是否有必要做以下事情？

__weak id weakSelf = self; [AFnetworking requestGet:@"http://www.website.com" completionBlock:(^)(RequestObj* request, NSError* error){ [weakSelf.tableView reloadData]; }];

或者AFNetworking是否有某种记忆魔法可以阻止这种情况？

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编辑Aaron Brager的礼貌

这里没有保留周期。 但是如果你这样做了，在完成块中，你应该将weakSelf转换回强引用，这样它就不会在你的完成块中途被解除分配。

id strongSelf = weakSelf; [strongSelf.tableView reloadData];

So I was reading How do I avoid capturing self in blocks when implementing an API? about how memory management works in regards to referencing self within a completion block and that got me thinking: will the following cause a retain cycle?

Pseudocode:

[AFnetworking requestGet:@"http://www.website.com" completionBlock:(^)(RequestObj* request, NSError* error){ [self.tableView reloadData]; }];

Ignoring syntax problems, does self.tableView cause a retain cycle? Is it necessary to do the following instead?

__weak id weakSelf = self; [AFnetworking requestGet:@"http://www.website.com" completionBlock:(^)(RequestObj* request, NSError* error){ [weakSelf.tableView reloadData]; }];

Or is there some sort of memory magic that AFNetworking does to prevent this?

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Edit courtesy of Aaron Brager

Here you don't have a retain cycle. But if you did, in the completion block, you should convert weakSelf back into a strong reference so it won't get deallocated halfway through your completion block.

id strongSelf = weakSelf; [strongSelf.tableView reloadData];

最满意答案

当两个或多个对象具有彼此强引用时，会发生保留周期。

在这种情况下，块将具有对self的强引用，但self没有对块的强引用，所以你在这里 没 问题 ， 也不需要使用 weakSelf 。

当你有一个保留周期并且需要通过使用weakSelf来打破它的weakSelf是当类具有对块的强引用时，如下例所示：

typedef void (^CompletionCallback)(RequestObj* request, NSError* error); @interface SomeClass() { /// Strong reference to the block CompletionCallback completionBlock; } @end @implementation SomeClass() - (void)someMethod { completionBlock = ^(RequestObj* request, NSError* error) { /// Strong reference to the class [self.tableView reloadData]; }; [AFnetworking requestGet:@"http://www.website.com" completionBlock:completionBlock]; } @end

在这个例子中， completionBlock和self都有相互之间的强引用，因此你在这里有一个保留周期，需要打破它。

A retain cycle occurs when two or more objects have strong references to each other.

In this case, the block will have a strong reference to self, but self doesn't have a strong reference to the block, so you are fine here and no need to use weakSelf.

The case when you'll have a retain cycle and need to break it by using the weakSelf is when the class has a strong reference to the block too like in the following example:

typedef void (^CompletionCallback)(RequestObj* request, NSError* error); @interface SomeClass() { /// Strong reference to the block CompletionCallback completionBlock; } @end @implementation SomeClass() - (void)someMethod { completionBlock = ^(RequestObj* request, NSError* error) { /// Strong reference to the class [self.tableView reloadData]; }; [AFnetworking requestGet:@"http://www.website.com" completionBlock:completionBlock]; } @end

In this example, both completionBlock and self have strong references to each other, and therefore you'll have a retain cycle here and need to break it.