methods in objective-c

Question

为什么有时需要将方法签名放入.h文件中，而有时却不需要呢？

Answer 1

This is just because some people like to put it in the header. Some people don't. You might have notice that in the .h files there is an @interface . You technically just need to put method signatures there. But, trust me, it makes life a lot easier if its in the header file (mostly because its more readable).

Answer 2

It's always a good idea to put the signature of your public methods in the .h file. You will avoid compiler warnings, and you'll know that if you do get a warning, it's for a good reason (you mistyped your method name, parameter type, etc).

Answer 3

It's always a good idea to declare methods in the @interface before using them (it helps the compiler, allowing the compiler to help you by catching more type errors), but the header file should really only have public methods (methods you want other classes to know about). For private methods that are used internally by the class, a class extension within the .m file is a good idea, ie:

@interface MyClass () 

-(void) superSecretMethod;

@end

Answer 4

Because technically objects have no methods in Objective-C as we know them from other languages, instead what you are doing is to send messages to the object, if there is a corresponding method (message) on the object with the same signature, it will be called. This means there is no real need to have the signatures in the header however it is good practice to have them so that the compiler can warn if you write the wrong signature.

Answer 5

Methods which you are overriding from your superclass do not need to be redeclared in your class's interface. It is sometimes a good idea to do so, but is not required.

Similarly, you do not need to declare methods that you are implementing from a protocol; simply declaring that you conform to the protocol is enough.

You should declare methods which are "new" to your class: those which are not inherited from a superclass nor part of a protocol. This is to give the compiler the necessary information to determine the correct argument and return types and is necessary to the correct running of your application.

Those answerers who have said that you don't have to declare your methods are technical correct, however be aware that this is a very bad practice as the compiler will infer parameter and return types which may not match the definition and can cause undefined behavior when the method is called.