PHP常用的设计模式

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本文介绍了四种常见的设计模式：工厂模式、单例模式、观察者模式和命令链模式，并通过PHP代码示例展示了每种模式的基本用法及其实现。

工厂模式：

工厂模式是一种类，它具有为您创建对象的某些方法。您可以使用工厂类创建对象，而不直接使用 new。这样，如果您想要更改所创建的对象类型，只需更改该工厂即可。使用该工厂的所有代码会自动更改。

<?php
interface IUser
{
  function getName();
}

class User implements IUser
{
  public static function Load( $id ) 
  {
        return new User( $id );
  }

  public static function Create( ) 
  {
        return new User( null );
  }

  public function __construct( $id ) { }

  public function getName()
  {
    return "Jack";
  }
}

$uo = User::Load( 1 );
echo( $uo->getName()."\n" );
?>

单元素模式

<?php
require_once("DB.php");

class DatabaseConnection
{
  public static function get()
  {
    static $db = null;
    if ( $db == null )
      $db = new DatabaseConnection();
    return $db;
  }

  private $_handle = null;

  private function __construct()
  {
    $dsn = 'mysql://root:password@localhost/photos';
    $this->_handle =& DB::Connect( $dsn, array() );
  }
  
  public function handle()
  {
    return $this->_handle;
  }
}

print( "Handle = ".DatabaseConnection::get()->handle()."\n" );
print( "Handle = ".DatabaseConnection::get()->handle()."\n" );
?>

观察者模式

<?php
interface IObserver
{
  function onChanged( $sender, $args );
}

interface IObservable
{
  function addObserver( $observer );
}

class UserList implements IObservable
{
  private $_observers = array();

  public function addCustomer( $name )
  {
    foreach( $this->_observers as $obs )
      $obs->onChanged( $this, $name );
  }

  public function addObserver( $observer )
  {
    $this->_observers []= $observer;
  }
}

class UserListLogger implements IObserver
{
  public function onChanged( $sender, $args )
  {
    echo( "'$args' added to user list\n" );
  }
}

$ul = new UserList();
$ul->addObserver( new UserListLogger() );
$ul->addCustomer( "Jack" );
?>

命令链模式

<?php
interface ICommand
{
  function onCommand( $name, $args );
}

class CommandChain
{
  private $_commands = array();

  public function addCommand( $cmd )
  {
    $this->_commands []= $cmd;
  }

  public function runCommand( $name, $args )
  {
    foreach( $this->_commands as $cmd )
    {
      if ( $cmd->onCommand( $name, $args ) )
        return;
    }
  }
}

class UserCommand implements ICommand
{
  public function onCommand( $name, $args )
  {
    if ( $name != 'addUser' ) return false;
    echo( "UserCommand handling 'addUser'\n" );
    return true;
  }
}

class MailCommand implements ICommand
{
  public function onCommand( $name, $args )
  {
    if ( $name != 'mail' ) return false;
    echo( "MailCommand handling 'mail'\n" );
    return true;
  }
}

$cc = new CommandChain();
$cc->addCommand( new UserCommand() );
$cc->addCommand( new MailCommand() );
$cc->runCommand( 'addUser', null );
$cc->runCommand( 'mail', null );
?>

文章来源：https://www.ibm.com/developerworks/cn/opensource/os-php-designptrns/