Single-Case mode

Singleton mode (duty mode):

Simply put, an object (before learning design patterns, need to understand the object-oriented thinking) is only responsible for a specific task;

Singleton class:

1. Theconstructor needs to be marked as private(access control: Prevent external code from creating objects using the new operator), the Singleton class cannot be instantiated in other classes, and can only be instantiated by itself;

2.have a static member variable that holds an instance of the class

3, has a public access to this instance of the static method (common getinstance () method to instantiate a singleton class, through the instanceof Operator can detect if the class has been instantiated)

In addition, you need to create a __clone () method to prevent the object from being copied (cloned)

Why use php Singleton mode?

1, php ,  So there's a lot of database operations in an app using singleton mode ,  new  The resources consumed by the operation.

2, If a class is required in the system to globally control some configuration information ,  .  This can be see Zf part.

3, in a page request ,  easy to debug Because all the code example Database Operations class DB) All concentrated in one class ,  We can set hooks in the class ,  output the log, thus avoiding everywhere var_dump,  echo

Code implementation:

<php

/1**

* Design pattern of a single case mode

* $_instance must be declared as a static private variable

* Constructors and destructors must be declared private to prevent external program new class to lose the meaning of a singleton pattern

* The getinstance () method must be set to public, this method must be called

* To return a reference to the instance

*:: operator can only access static variables and static functions

* New objects will consume memory

* Usage Scenario: The most common place is the database connection.

* Once an object is generated using singleton mode,

* This object can be used by many other objects .

*/

class Danli {

To save a static member variable for a class instance

private static $_instance;

How to construct private tags

Private Function __construct () {

Echo ' This is a constructed method; ' ;

}

To create a __clone method to prevent an object from being cloned

Public Function __clone () {

Trigger_error (' Clone is not allow! ' , e_user_error);

}

A singleton method, a public static method for accessing an instance

public static function getinstance() {

If(! (self::$_instance instanceof self)){

Self::$_instance = new self;

}

Return self::$_instance;

}

Public Function Test () {

Echo ' Invoke method succeeded ';

}

}

Class with new instantiation of private tag constructor will error

$danli = new Danli ();

Correct method, use double colon:: operator to access the static method to get the instance

$danli = Danli::getinstance();

$danli->test ();

Copying (cloning) an object will result in a e_user_error

$danli _clone =Clone$danli; 

Single-Case mode