The difference between an eye and an extension like iOS

Category: Adds a new method to an existing class. (Only methods can be added and instance variables cannot be added)

To add a method:

COMMAND + n---->objective-c File----->file Type (category)

Purpose: Commonly used to add methods to system classes.

Extension (extension): is to define your own private method. (You can add a method, or an instance variable)

To add a method:

COMMAND + n---->objective-c File----->file Type (extension)

or directly under the. m file of the class

@interface mineviewcontroller ()

Write an extended method or instance variable

@end

Purpose: Used to add a method to a custom class, instance variable. Or add a method to an existing class, instance variable.

The difference between an eye and an extension like iOS