如何在OC中正确声明block

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) {...};