iOS Block弱引用

先weak再strong.可以很好的管理Block内部对self的引用

常规写法

 __weak typeof(self) weakSelf = self;
    self.Button.rac_command = [[RACCommand alloc] initWithEnabled:textSig signalBlock:^RACSignal *(NSString * input) {

        __strong typeof(weakSelf) strongSelf = weakSelf;
        return nil;
    }];

装逼写法

定义两个宏

#ifndef weakify
#if DEBUG
#if __has_feature(objc_arc)
#define weakify(object) autoreleasepool{} __weak __typeof__(object) weak##_##object = object;
#else
#define weakify(object) autoreleasepool{} __block __typeof__(object) block##_##object = object;
#endif
#else
#if __has_feature(objc_arc)
#define weakify(object) try{} @finally{} {} __weak __typeof__(object) weak##_##object = object;
#else
#define weakify(object) try{} @finally{} {} __block __typeof__(object) block##_##object = object;
#endif
#endif
#endif

#ifndef strongify
#if DEBUG
#if __has_feature(objc_arc)
#define strongify(object) autoreleasepool{} __typeof__(object) object = weak##_##object;
#else
#define strongify(object) autoreleasepool{} __typeof__(object) object = block##_##object;
#endif
#else
#if __has_feature(objc_arc)
#define strongify(object) try{} @finally{} __typeof__(object) object = weak##_##object;
#else
#define strongify(object) try{} @finally{} __typeof__(object) object = block##_##object;
#endif
#endif
#endif

    @weakify(self)
    [self dismissViewControllerAnimated:true completion:^{
       @strongify(self)
        
        [self.btn setTitle:@"弱引用" forState:UIControlStateNormal];
    }];