Black Horse programmer ___ loading and initialization of OC classes

Constructor

Two steps are required to create an available object.

1. Allocate storage space + alloc

2. initialize-init

Person * P1 = [person alloc]

Person * P2 = [P1 init]

It is equivalent to: person * P = [person new]. However, although this method can quickly create a new object, it cannot initialize the new object.

Sometimes all the objects we want to create have an initial value. At this time, we can rewrite the constructor.

-(ID) Init {// you must call back the super init method to initialize some member variables declared in the parent class and other attributes self = [Super init]; // If the initialization is successful, it is necessary to initialize if (self! = Nil) {_ age = 10; // make the created age attributes equal to 10} return self ;}

Notes for rewriting Constructor

1. First call the constructor of the parent class [Super init]

2. initialize the member variables in the subclass.

Supplement:

ID: a universal pointer that can point to any OC object.

Class Nature

The class itself is also an object of the class type, referred to as the class Object Class C = [person class], and uses the class to create the person object.

Class loading and initialization

When the program starts, all classes and categories in the project will be loaded, and the + load method for each class and category will be called back, and only once

When an object is created using a class for the first time, the + initialize method of the current class is called, that is, the initialization object, so that the created object can be used

Rule:

When the program starts, the system first loads the parent class and then the Child class (first calls the + load method of the parent class, and then calls the + load method of the Child class)

Initialize the parent class first, and then initialize the subclass (first call the + initialize method of the parent class, and then call the + initialize method of the subclass)

Sel

SEL is a method packaging. It encapsulates the method into a sel type data and finds the corresponding method address. You can find the method address to call the method.

[P test]-> directly call the test method

Sel S = @ selector (test)

[P performselector: S]-> indirect call of the test method

In the method, _ cmd indicates the SEL value of the current method. Therefore, using _ CMD in the method implementation will lead to an endless loop, for example:

-(Void) Test2 {// _ cmd indicates the current method nsstring * STR = nsstringfromselector (_ cmd); // it will lead to an endless loop // [self defined mselector: _ cmd]; nslog (@ "Test2 method called ----- % @", STR );}

Black Horse programmer ___ loading and initialization of OC classes