Block

转自：http://goshdarnblocksyntax.com/
As a local variable:
returnType (^blockName)(parameterTypes) = ^returnType(parameters) {...};
As a property:

@property (nonatomic, copy, nullability) returnType (^blockName)(parameterTypes);
As a method parameter:

• (void)someMethodThatTakesABlock:(returnType (^nullability)(parameterTypes))blockName;
  As an argument to a method call:

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

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