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HomeBackend DevelopmentPHP Tutorial学习php设计模式 php实现状态模式_PHP

一、意图
允许一个对象在其内部状态改变时改变它的行为。对象看起来似乎修改了它的类
状态模式变化的位置在于对象的状态

二、状态模式结构图

三、状态模式中主要角色
抽象状态(State)角色:定义一个接口,用以封装环境对象的一个特定的状态所对应的行为
具体状态(ConcreteState)角色:每一个具体状态类都实现了环境(Context)的一个状态所对应的行为
环境(Context)角色:定义客户端所感兴趣的接口,并且保留一个具体状态类的实例。这个具体状态类的实例给出此环境对象的现有状态
四、状态模式的优点和缺点
1、它将与特定状态相关的行为局部化
2、它使得状态转换显示化
3、State对象可被共享
五、状态模式适用场景
1、一个对象的行为取决于它的状态,并且它必须在运行时刻根据状态改变它的行为
2、一个操作中含有庞大的多分支的条件语句,且这些分支依赖于该对象的状态。这个状态通常用一个或多个枚举常量表示。通常,有多个操作包含这一相同的条件结构。State模式模式将每一个条件分支放入一个独立的类中。这使得你可以要所对象自身的情况将对象的状态作为一个对象,这一对象可以不依赖于其他对象而独立变化
六、状态模式与其它模式
单例模式(singleton模式):具体状态对象通常是单例模式
享元模式(flyweight模式):享元模式解释了何时以及怎样共享状态对象
七、状态模式PHP示例

<&#63;php
/**
 * 抽象状态角色
 */
interface State {
 
  /**
   * 方法示例
   */
  public function handle(Context $context);
}
 
/**
 * 具体状态角色A
 * 单例类
 */
class ConcreteStateA implements State {
  /* 唯一的实例 */
  private static $_instance = null;
 
  private function __construct() {
 
  }
 
  /**
   * 静态工厂方法,返还此类的唯一实例
   */
  public static function getInstance() {
    if (is_null(self::$_instance)) {
      self::$_instance = new ConcreteStateA();
    }
 
    return self::$_instance;
  }
 
  public function handle(Context $context) {
    echo 'Concrete Sate A handle method<br />';
    $context->setState(ConcreteStateB::getInstance());
  }
 
}
 
/**
 * 具体状态角色B
 * 单例类
 */
class ConcreteStateB implements State {
  /* 唯一的实例 */
 
  private static $_instance = null;
 
  private function __construct() {
  }
 
  /**
   * 静态工厂方法,返还此类的唯一实例
   */
  public static function getInstance() {
    if (is_null(self::$_instance)) {
      self::$_instance = new ConcreteStateB();
    }
 
    return self::$_instance;
  }
 
  public function handle(Context $context) {
    echo 'Concrete Sate B handle method<br />';
    $context->setState(ConcreteStateA::getInstance());
  }
 
}
 
/**
 * 环境角色
 */
class Context {
 
  private $_state;
 
  /**
   * 默认为StateA
   */
  public function __construct() {
    $this->_state = ConcreteStateA::getInstance();
  }
 
  public function setState(State $state) {
    $this->_state = $state;
  }
 
  public function request() {
    $this->_state->handle($this);
  }
 
}
 
/**
 * 客户端
 */
class Client {
 
  /**
   * Main program.
   */
  public static function main() {
    $context = new Context();
    $context->request();
    $context->request();
    $context->request();
    $context->request();
  }
 
}
 
Client::main();
&#63;>

以上就是使用php实现状态模式的代码,还有一些关于状态模式的概念区分,希望对大家的学习有所帮助。

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