Objective-C/Blocks - 这不是一个保留周期吗？

Question

@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

我认为这段代码创建了一个保留周期,因为块在块中-longRunningTaskWithCompletion:捕获self(设置字符串属性)并将块添加到dispatch queue属性.

Answer 1

有一个保留周期,但这是暂时的.保留周期如下所示:

• self 保留 dispatchQ
• dispatchQ 保留块
• 块保留 self

当块返回时,dispatchQ释放它.此时,保留周期被打破.该块被解除分配并释放self.