__block : 理解-优快云博客

本文通过一个具体的Objective-C代码示例，深入探讨了不同类型的对象（如实例对象、全局对象、静态对象等）在内存中的管理方式。文章还展示了如何使用_block对象以及块(Block)内的对象引用，并分析了它们对内存计数的影响。

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转：http://blog.youkuaiyun.com/hherima/article/details/38620175

@interface ViewController(){
    NSObject* _instanceObj;
}

@implementation ViewController
- (void) viewDidLoad
{
    _instanceObj = [[NSObject alloc] init];

    static NSObject* __staticObj = nil;
    __globalObj = [[NSObject alloc] init];
    __staticObj = [[NSObject alloc] init];

    NSObject* localObj = [[NSObject alloc] init];
    NSLog(@"localObj count = %d", _objc_rootRetainCount(localObj));

    __block NSObject* blockObj = [[NSObject alloc] init];

    typedef void (^MyBlock)(void);
    MyBlock aBlock = ^{
        NSLog(@"%@", __globalObj);
        NSLog(@"%@", __staticObj);
        NSLog(@"%@", _instanceObj);
        //NSLog(@"%@", localObj);
        NSLog(@"localObj count = %d", _objc_rootRetainCount(localObj));
        NSLog(@"%@", blockObj);
    };

    //aBlock = [aBlock copy];
    aBlock();

    NSLog(@"%d", _objc_rootRetainCount(__globalObj));
    NSLog(@"%d", _objc_rootRetainCount(__staticObj));
    NSLog(@"%d", _objc_rootRetainCount(_instanceObj));
    NSLog(@"%d", _objc_rootRetainCount(localObj));
    NSLog(@"localObj count = %d", _objc_rootRetainCount(localObj));
    NSLog(@"%d", _objc_rootRetainCount(blockObj));
...