如何在Objective-C中声明Block?

局部变量:

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

类属性(property):

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

方法声明中的参数:

- (void)someMethodThatTakesABlock:(returnType (^)(parameterTypes))blockName;

方法调用中的参数:

[someObject someMethodThatTakesABlock:^returnType (parameters) {...}];

typedef的方式:

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