Objective-C Learning 1

First of all, to learn objective-C (hereinafter referred to as OC) Well, you must have the foundation of C language, because OC is a superset of C language and OC is a process-oriented language. [C language is an object-oriented language]. Many syntaxes in OC are similar to those in C language. OC can be fully compatible with C language to achieve mixed Compiling. To learn OC well, it is best to have a C language basis. (If you have C ++ basics or ideas, you can learn OC better)

1. All files in OC are stored as. M files, and Declaration files are. H files like C files;

Personal reminder: whether it is C or oC, it is best to use the camper ID for some identifiers;

Creation class:

Class Name:GenerallyUppercase;

To define a class:1. Define the class name; 2. Compile the class attributes ---> (instance variable); 3. Compile the class behavior ---> method;

Tip: Generally, the class name should be the same as the file name for programmers to understand. The attribute declaration in a general class starts with an underscore because the global variable is declared here, convenience: duplicate the keyword in the local variable; only variables can be declared here, and no value can be assigned;

Method definition:

-(Void) method: (INT) arguments;

-(Method type: instance method, also called object method)

+ (Class method)

(Void) return value; no return value is void;

Method method name;

(INT "type"): parameter types are included;

Arguments: parameter name;

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The method definition is divided into: Without parameters, such as-(void) Shoping;

With one parameter: void (Shoping) :( float) price;

There are two parameters: void (shopping) :( float) price :( float) weight;

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Method implementation:@ Implementation in. m

// Write the implementation of the method here;

-(Void) Shopping :( float) price {

Nslog (@ "I'm shopping! ");

}

@ End;

And then apply it to the main function.

# Import "person. H"

Int main (){

//Create an object using the class name;

// Person * person = [person alloc];

// Person = [person init];

//Alloc applies for a space area in the memory to store the object information;

// Call the init method below to initialize some default data;

Person * person = [[person alloc] init]; // nest two steps together;

//The variables are declared through class type on the left, and the objects are created on the right;

++ ++

// The previous section defines the class and creates an object with the class;

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There is also a method for creating objects:

Person * person2 = [person new]; (this method is not recommended in OC)

This method is generally used: person * person1 = [[person alloc] init];

_______________________

Call methods in the object;

-The instance method (or object method) starts with +: class method;

-Objects must start with person1)

Run the following command in main:
[Person1 shopping: 200]; // 200 is a parameter
It will enter the shopping function;
// This indicates that the shopping instance method is called; the instance method must have an object before it can be called;
// Many methods can be created through the class;

----------------------------------

After creating the object person1;

Set the name and age;

No way to directly set the name and method, onlySet attributes using methods;

Method To set the name:-(void) setname :( nsstring *) Name; // method description:Set attributesName;

Implementation: In the. M file:

-(Void) setname :( nsstring *) name {

_ Name = Name;

}

----------------------------------

Return to main and set the name:

[Person1 setname: @ "Zhang San"]; // input the Zhang San string to the name function, and then pass the name of Zhang San to the _ name function;

-----------------------------------

Attribute: it is also called a member variable, a global variable, or an instance variable. global variables can be used in all methods;

----------------

The method used to set attributes is called the setter method or the set method;
The method for obtaining attributes from the outside is called the get method, which has a return value;

-----------------------------------

For example,-(nsstring *) Name;
 
-(Nsinteger) age;
Implementation:
-(Nsstring *) name {
Return _ name;
}
-(Nsinteger) Age {
Return _ age;
}
Call: nsstring * name1 = [person1 name]

++ ++

It used to be a parameter method. Learn it todayMultiple Parameter Methods;

-----------------

-(Void) setname :( nsstring *) Name setage :( nsinteger *) age; // method name has two parts: setname and setage. setage can be saved here (but not recommended );

Implementation:-(void) setname :( nsstring *) Name setage :( nsinteger *) Age {

_ Name = Name;

_ Age = age;

} // This is not generally defined here. It is only used for demonstration;Generally, a variable defines a setting method.;

Call: [person1 setname: @ "Zhang San" setage: 22]; [object call Method !]

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[Switch between. M and. H] command + cotrl + up and down keys. The Tab key can complete the keywords or identifiers we have written;

----------------

Method Type:-object method, + class method;

+: Class Method

Call the method using the class name; call it a class method;
Method Description: used to create a person object;
Define the class method: + (person *) newperson;
Implementation Method: + (person *) newperson {
Person * P = [[person alloc] init];
// Some variables can be initialized here
// [P setname: @ "zhangsan" setage: 22]
}
Call class: person * person3 = [person newperson];

--------------------------------

If no object is created, properties cannot be used;

No instance objects. Where are the attributes?

Objects must be available for use;

// Attributes cannot be accessed in class methods;

Attribute: who calls the method attribute and belongs to whom; ++ ++

Create a complementary object;
When an object is created, its member variables are not initialized. What are their default values?
@ Interface person: nsobject
Int _ age;

// The system initializes it as byte: 0; short: 0; INT: 0; long 0l; CHAR: \ u0000 '; float: 0.0f; double: 0.0d; bollean: false; All pointers: NIL;

@ End

++ ++