Introduction to classes and objects in Objective-c

Knowledge points

1. Introduction to Classes

A class is the type of an object that is an instance of a type.

Instance variables: Used to distinguish between different objects of the same class, which are used to describe objects. Instance variables can be of various types: basic data types, pointers, composite types, and other classes.

Instance method: A function used to manipulate an object of a class, and an instance method is to give an external access interface.

In OC, use #import to include the header file. Prevents header files from being included repeatedly.

2. Declarations of classes

@interface Classname:parentclass<protocol,.. >

{

• Declaration of an instance variable

}

Method declarations//Declaration of methods

@end

3. Declaration of methods:

Mtype (returntype) Name: (type) param name1: (type1) param1 ....

Method type return value type label name parameter type parameter and first name

Example:-(ID) initwithx: (int) _x AndY: (int) _y;

• • + (int) allnum;

Object method:-Begins with an object that can be called only by an instance of the object, which accesses instances of the current object.

Class method: The + sign can only be called by a class, and the instance variable cannot be accessed in a class method.

4. Messaging mechanisms

General format for sending messages in OC: [receiver message];

[Instance object instance method];

[Class-Class method];

5. Attribute declarations

The syntax for declaring a property is: @property (parameter 1, parameter 2) type name;

Example: @property (nonatomic, retain) Circle *circle;

The parameters are divided into three main categories:

Read-Write properties: (readwrite/readonly)

Setter semantics: (assign/retain/copy/strong/weak)

Atomicity: (atomic/nonatomic)

Each parameter has the following meanings:

ReadWrite: Producing Setter/getter method;

ReadOnly: Only the Getter method is generated;

Assign: The default type, the setter method in the instance variable directly assigned value, do not perform retain operation, the main operation of the basic data type.

Retain: Shallow copy, copy the memory address of the object, so that the target object pointer and source object point to the same piece of memory space.

Copy: Deep copy, copy the specific contents of the object to a newly opened space.

New properties in Strong:arc, similar to retain, when multiple pointers point to the same piece of memory, the memory is not freed as long as there is a pointer to that memory.

New properties in Weak:arc, similar to assign, when multiple pointers point to the same piece of memory, the memory is freed as long as one does not point to that memory.

Nonatomic: Disables multi-threading and improves performance.

Atomic: When using multi-threading, to prevent two threads from waiting for each other to cause deadlocks, use atomic, but consume a certain amount of resources.

Introduction to classes and objects in Objective-c