Class extension in OC

The extension of OC classes is summarized as follows:

There are 4 in total:

1. subClass

Purpose: You can use class inheritance to add the variables and methods of the parent class.

Statement: In the. h file

@ Interface Student: Person

2. Category

Function: you can add a parent class, but cannot define variables. It is often used to extend the parent class without knowing the source code.

Syntax: In the. h and. m files, the file name is in the format of "parent class name + category name.

After @ interface @ implementation, "parent class name (category name )"

3. Extension

Purpose: Define private methods. You can hide methods that are not published. Mostly used to hide some intermediate steps.

Written in: implemented before @ implementation in the. m file

@ Interface Person () {NSString * _ age ;}
-(Void) aa;
@ End in this way, the private method is defined.

4. protocol

Purpose: implement methods similar to multiple inheritance. A class complies with multiple protocols. Statement: the Protocol only has. H files, and the method is defined. @ Required // required by default
-(Void) method1;

-(Void) method2;

@ Optional // optional

-(Void) method3;

Currently, we will continue to add more.