1. Block是否一定会造成循环引用
根据上篇文我们知道，循环引用的关键是:相互强引用,如果没有达到这一必要条件，则block不会造成循环引用
两个简单的例子:
@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]; // 会造成循环引用，因为self->Block, block -> self self.testBlock1 = ^{ NSLog(@"== self = %p",self); }; //不会造成循环引用，因为只有self->block self.testBlock2 = ^{ }; } - (void)dealloc { NSLog(@"dealloc = %@", self); } @end
编译成cpp源码:
testBlock0
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)));
testBlock1:
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)));
或者如下:也不会造成循环引用，虽然block持有self，但self没有持有block
BlockViewController2 *vc = [[BlockViewController2 alloc] init]; [self.navigationController pushViewController:vc animated:true]; vc.testBlock10 = ^{ NSLog(@"-----vc.testBlock10 = %p", self); };
2. UIView动画是否会造成循环引用
不会，+ (void)animateWithDuration:(NSTimeInterval)duration animations:是类方法，当前控制器无法强引用一个类，所以循环引用无法构成
3. Masonry是否会造成循环引用
不会 ， self持有了Masonry,但是Masonry源码中并没有持有View,,如果将源码的block(constrainMaker)改成self.block = block(constrainMaker)，那么此时view才会持有block，才会造成循环引用
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源码: - (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *))block { self.translatesAutoresizingMaskIntoConstraints = NO; MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc] initWithView:self]; block(constraintMaker); return [constraintMaker install]; }
4. AFN 是否会造成循环引用
项目中用到AFN的代码
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); } }];
AFN源码
- (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; }
可见： self并没有持有manager， dataTask也没有持有success和failure这两个block，即使block中持有了self。也不会构成循环引用
