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Object-C 中声明一个Block，共有四种类型

1、声明一个局部Block

NSString * (blockName)(NSString *) = ^ NSString* (NSString* ){ return};

2、声明一个Block属性变量

@property (nonatomic, copy)  NSString * ( ^blockName )(NSString *)

3、block作为一个函数的输入参数(省去了blockName)

- (void) someMethodThatTakesBlock:( NSString * (^)(NSString *) )blockName;

4、block作为回调对象而存在(省去了blockName)

[someObj someMethodThatTakesBlock: ^ NSString * (NSString *){...}];

5、宏定义TypedefBlock

typedef NSString* (TypeName)(NSString *);
TypeName blockName = ^NSString* (NSString* ){...};