OC Section nineth class Extension

1. Category Category

①. class is to add a method to a class inside the system or to a class that does not have source code, and cannot add an instance variable

② . The added method is referred to as part of the original class, and subclasses can still use the

　　③. class Destination file name is original + file name (for example: Nsstring+wuyaun)

　　④. you can either add an instance method or add a class method

2, Extension extension

①. extensions are for custom classes that extend the functionality of the

②. above the . M file, build the extension using the @interface keyword

③.　　 in the extension, we can either declare a method or declare an instance variable or property

④.　　 the added content belongs to the private part of this class.

3, delegate agreement, agent execution.

@class A; // tell compiler a is just a class name, as to what instance variables, properties, methods are not known in the class

4. polymorphic Applications

//Polymorphic , is a variety of forms, There are many states there must be inheritance

//The nature of polymorphism is that the parent pointer points to the child class object

//polymorphic use, the system dynamically monitors what type the pointer is pointing to, althoughcar is a car * type pointer, but when car executes the method alone, TA is the Benz object

// parent pointer as a function or a parameter to a method, when executing a method or invoking a function, passing in a specific subclass object, you can execute methods such as.

Polymorphic Disadvantage, the parent pointer must be able to execute a subclass of methods, can only perform inherited methods, if you want to use, you have to do a strong turn.

OC Section nineth class Extension