1.深入研究Block用weakSelf、strongSelf、@weakify、@strongify解决循环引用

http://ios.jobbole.com/88708/

2.Objective-C 中涉及到的Block的写法：

局部变量returnType (^blockName)(parameterTypes) = ^returnType(parameters) {...};

作为属性（property）@property (nonatomic, copy) returnType (^blockName)(parameterTypes);

作为方法参数:- (void)someMethodThatTakesABlock:(returnType (^)(parameterTypes))blockName;

作为方法调用的参数：[someObject someMethodThatTakesABlock:^returnType (parameters) {...}];

自定义 typedef:typedef returnType (^TypeName)(parameterTypes);TypeName blockName = ^returnType(parameters) {...};

3.Swift 中Block解除循环引用的写法：

someQueue.async { [weak self] in

            guard let ss = self else {

                return

            }

}