ARC中__block关键字修饰的local变量在Block中不会被强引用

实验代码：

- (void)testLocalObj
{
    NSObject* localObject = [[NSObject alloc] init];

    printf("localObject address out block: %p\n", localObject);
    
    void (^TestBlock)(void) = ^{
        printf("localObject address in block: %p\n", localObject);
    };
    
    localObject = nil;
    TestBlock();
}



- (void)testBlockObj
{
    __block NSObject* blockObject = [[NSObject alloc] init];

    printf("blockObject address out block: %p\n", blockObject);
    
    void (^TestBlock)(void) = ^{
        printf("blockObject address in block: %p\n", blockObject);
    };
    
    blockObject = nil;
    TestBlock();
}



- (void)testWeakObj

{
    NSObject* object = [[NSObject alloc] init];
    __weak NSObject *weakObject = object;
    
    printf("weakObject address out block: %p\n", weakObject);
    
    void (^TestBlock)(void) = ^{
        printf("weakObject address in block: %p\n", weakObject);

    };

    object = nil;
    TestBlock();
    
}
           

输出结果：

localObject address out block: 0x8f5cfd0
localObject address in block: 0x8f5cfd0
blockObject address out block: 0x8f5cfd0
blockObject address in block: 0x0
weakObject address out block: 0x8f5cfd0
weakObject address in block: 0x0