Objective-C/块-这不是保留周期吗? [英] Objective-C / Blocks - Isn't this a retain cycle?

问题描述

@interface ClassA : NSObject

@property (strong, nonatomic) dispatch_queue_t dispatchQ;
@property (strong, nonatomic) NSString *string;

@end

@implementation ClassA

- (id)init
{
    self = [super init];
    if (self) {
        _dispatchQ = dispatch_queue_create("com.classa.q", NULL);
    }

    return self;
}

- (void)longRunningTaskWithCompletion:(void(^)(void))completion
{
    dispatch_async(self.dispatchQ, ^{

        for (int i = 0; i < 10000; i++) {
            NSLog(@"%i", i);
        }

        dispatch_sync(dispatch_get_main_queue(), ^{
            self.string = @"Class A Rocks!";

            if(completion) {
                completion();
            }
        });
    });
}

@end

我想这段代码会创建一个保留周期，因为-longRunningTaskWithCompletion:中的块将自身(设置字符串属性)捕获到一个块中并将该块添加到调度队列属性中.

I'm thinking this code creates a retain cycle because the block in -longRunningTaskWithCompletion: captures self (to set the string property) in a block and adds the block to the dispatch queue property.

推荐答案

有一个保留周期，但这是临时的.保留周期如下:

There is a retain cycle, but it's temporary. The retain cycle looks like this:

• self保留dispatchQ
• dispatchQ保留该块
• 该图块保留self

• self retains dispatchQ
• dispatchQ retains the block
• the block retains self

当块返回时，dispatchQ释放它.在这一点上，保留周期被打破了.释放该块并释放self.

When the block returns, dispatchQ releases it. At that point, the retain cycle is broken. The block is deallocated and releases self.

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