设计模式之状态模式

/**
*环境类
*/
class Context{
    public $stateFlag;
    private $state;
    
    public function setState(State $state){
        $this->state = $state;
    }
    
    public function request(){
        $this->state && $this->state->handle($this);
    }
}

/**
*抽象状态类
*/
abstract class State{
    
    public abstract function handle(Context $context);
}

/**
*状态A
*/
class ConcreteStateA extends State{
    public function handle(Context $context){
        if(1 == $context->stateFlag){
            echo 'State flag is 1, so do stateA action<br>';
        }else{
            $stateB = new ConcreteStateB();
            $context->setState($stateB);
            $context->request();
        }
    }
}

/**
*状态B
*/
class ConcreteStateB extends State{
    public function handle(Context $context){
        if(2 == $context->stateFlag){
            echo 'State flag is 2, so do stateB action<br>';
        }
    }
}

$context = new Context();
$context->stateFlag = 1;
$stateA = new ConcreteStateA();
$context->setState($stateA);
$context->request();
$context->stateFlag = 2;
$context->request();