咱們知道，循環引用即: 當兩個對象A和B，分別強引用對方，那麼就會產生循環引用。即A釋放的時候必須先釋放B，而B釋放的時候必須釋放A。致使誰也不能釋放而打破循環引用的方法就是其中一方弱引用另外一方async

#1. Block是否必定會形成循環引用根據上篇文咱們知道，循環引用的關鍵是:相互強引用,若是沒有達到這一必要條件，則block不會形成循環引用post

兩個簡單的例子:動畫

@interface BlockViewController ()

@property (nonatomic, copy) NSString *nickname;

@property (nonatomic, copy) void(^ testBlock1)(void);

@property (nonatomic, copy) void(^ testBlock2)(void);

@end

@implementation BlockViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor orangeColor];
    
    // 會形成循環引用，由於self->Block, block -> self
    self.testBlock1 = ^{
        NSLog(@"== self = %p",self);
    };

    //不會形成循環引用，由於只有self->block
    self.testBlock2 = ^{
    };
}

- (void)dealloc {
    NSLog(@"dealloc = %@", self);
}

@end

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編譯成cpp源碼:atom

testBlock0spa

struct __BlockViewController__viewDidLoad_block_impl_0 {
  struct __block_impl impl;
  struct __BlockViewController__viewDidLoad_block_desc_0* Desc;
  BlockViewController *self;
  __BlockViewController__viewDidLoad_block_impl_0(void *fp, struct __BlockViewController__viewDidLoad_block_desc_0 *desc, BlockViewController *_self, int flags=0) : self(_self) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
static void __BlockViewController__viewDidLoad_block_func_0(struct __BlockViewController__viewDidLoad_block_impl_0 *__cself) {
  BlockViewController *self = __cself->self; // bound by copy

        NSLog((NSString *)&__NSConstantStringImpl__var_folders_44_1ht3l6g55dv59_5s62wsv_bm0000gn_T_BlockViewController_439f5f_mi_0,self);
    }
    
        ((void (*)(id, SEL, void (*)()))(void *)objc_msgSend)((id)self, sel_registerName("setTestBlock1:"), ((void (*)())&__BlockViewController__viewDidLoad_block_impl_0((void *)__BlockViewController__viewDidLoad_block_func_0, &__BlockViewController__viewDidLoad_block_desc_0_DATA, self, 570425344)));
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testBlock1:code

struct __BlockViewController__viewDidLoad_block_impl_1 {
  struct __block_impl impl;
  struct __BlockViewController__viewDidLoad_block_desc_1* Desc;
  __BlockViewController__viewDidLoad_block_impl_1(void *fp, struct __BlockViewController__viewDidLoad_block_desc_1 *desc, int flags=0) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
static void __BlockViewController__viewDidLoad_block_func_1(struct __BlockViewController__viewDidLoad_block_impl_1 *__cself) {

    }

    ((void (*)(id, SEL, void (*)()))(void *)objc_msgSend)((id)self, sel_registerName("setTestBlock2:"), ((void (*)())&__BlockViewController__viewDidLoad_block_impl_1((void *)__BlockViewController__viewDidLoad_block_func_1, &__BlockViewController__viewDidLoad_block_desc_1_DATA)));
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或者以下:也不會形成循環引用，雖然block持有self，但self沒有持有blockorm

BlockViewController2 *vc = [[BlockViewController2 alloc] init];
    [self.navigationController pushViewController:vc animated:true];
    vc.testBlock10 = ^{
        NSLog(@"-----vc.testBlock10 = %p", self);
    };
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2. UIView動畫是否會形成循環引用

不會，+ (void)animateWithDuration:(NSTimeInterval)duration animations:是類方法，當前控制器沒法強引用一個類，因此循環引用沒法構成對象

3. Masonry是否會形成循環引用

不會， self持有了Masonry,可是Masonry源碼中並無持有View,,若是將源碼的block(constrainMaker)改爲self.block = block(constrainMaker)，那麼此時view纔會持有block，纔會形成循環引用get

self.testButton = [UIButton buttonWithType:UIButtonTypeCustom];
    [self.view addSubview:self.testButton];
    [self.view mas_makeConstraints:^(MASConstraintMaker *make) {
        make.centerX.equalTo(self.view);
        make.centerY.equalTo(self.view);
        make.size.mas_equalTo(CGSizeMake(100, 50));
    }];
 
 Masonry源碼:
- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *))block {
    self.translatesAutoresizingMaskIntoConstraints = NO;
    MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc] initWithView:self];
    block(constraintMaker);
    return [constraintMaker install];
}
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4. AFN 是否會形成循環引用

項目中用到AFN的代碼

AFHTTPSessionManager * manager = [AFHTTPSessionManager manager];
    [manager POST:completeURL parameters:params progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
        if (success) {
            success(responseObject);
        }
    } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
        if (failure) {
            failure(error);
        }
    }];
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AFN源碼

- (NSURLSessionDataTask *)POST:(NSString *)URLString
                    parameters:(id)parameters
                      progress:(void (^)(NSProgress * _Nonnull))uploadProgress
                       success:(void (^)(NSURLSessionDataTask * _Nonnull, id _Nullable))success
                       failure:(void (^)(NSURLSessionDataTask * _Nullable, NSError * _Nonnull))failure
{
    NSURLSessionDataTask *dataTask = [self dataTaskWithHTTPMethod:@"POST" URLString:URLString parameters:parameters uploadProgress:uploadProgress downloadProgress:nil success:success failure:failure];

    [dataTask resume];

    return dataTask;
}

- (NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)method
                                       URLString:(NSString *)URLString
                                      parameters:(id)parameters
                                  uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgress
                                downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgress
                                         success:(void (^)(NSURLSessionDataTask *, id))success
                                         failure:(void (^)(NSURLSessionDataTask *, NSError *))failure
{
    NSError *serializationError = nil;
    NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];
    if (serializationError) {
        if (failure) {
            dispatch_async(self.completionQueue ?: dispatch_get_main_queue(), ^{
                failure(nil, serializationError);
            });
        }

        return nil;
    }

    __block NSURLSessionDataTask *dataTask = nil;
    dataTask = [self dataTaskWithRequest:request
                          uploadProgress:uploadProgress
                        downloadProgress:downloadProgress
                       completionHandler:^(NSURLResponse * __unused response, id responseObject, NSError *error) {
        if (error) {
            if (failure) {
                failure(dataTask, error);
            }
        } else {
            if (success) {
                success(dataTask, responseObject);
            }
        }
    }];

    return dataTask;
}
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可見： self並無持有manager， dataTask也沒有持有success和failure這兩個block，即便block中持有了self。也不會構成循環引用

iOS - Block循環引用

2. UIView動畫是否會形成循環引用

3. Masonry是否會形成循環引用

4. AFN 是否會形成循環引用