简介

跟状态机密切相关。无限状态机 FSM 蕴含 状态、事件、动作三个元素。

当产生一个事件时，引发老状态变成新状态，并执行一个动作。

状态和行为间个别是有限度的，如某些行为只能再某些状态下进行，某些状态只能触发某些行为。

简略的状态间转换可应用 if else。

更有条理的能够用查表法：二维表中纵向是状态，横向是事件，value则是新状态和动作。做成二维数组配置，事件产生时联合以后状态，组成老状态索引去查二维表，得出value是新状态和动作，如果没有value则不变换

再简单一些之后，可应用状态模式。

角色

  • Context 上下文

    可视为状态机，其外部持有State援用

    可通过扭转State的值，来达到扭转Context行为的目标

  • 形象 State
  • 具体 State

类图

如图，Context/Machine中能够changeState来扭转以后的状态，其中doThis和doThat签名与State统一，这样看起来就像扭转状态的同时，扭转了Context的行为。

代码

class Context{    private $state;    public function __construct(State $state)    {        $this->transitionTo($state);    }    public function transitionTo(State $state): void    {        echo "Context: Transition to " . get_class($state) . ".\n";        $this->state = $state;        $this->state->setContext($this);    }    public function request1(): void    {        $this->state->handle1();    }    public function request2(): void    {        $this->state->handle2();    }}abstract class State{    protected $context;    public function setContext(Context $context)    {        $this->context = $context;    }    abstract public function handle1(): void;    abstract public function handle2(): void;}class ConcreteStateA extends State{    public function handle1(): void    {        echo "ConcreteStateA handles request1.\n";        echo "ConcreteStateA wants to change the state of the context.\n";        $this->context->transitionTo(new ConcreteStateB());    }    public function handle2(): void    {        echo "ConcreteStateA handles request2.\n";    }}class ConcreteStateB extends State{    public function handle1(): void    {        echo "ConcreteStateB handles request1.\n";    }    public function handle2(): void    {        echo "ConcreteStateB handles request2.\n";        echo "ConcreteStateB wants to change the state of the context.\n";        $this->context->transitionTo(new ConcreteStateA());    }}$context = new Context(new ConcreteStateA());$context->request1();$context->request2();

output:

Context: Transition to ConcreteStateA.ConcreteStateA handles request1.ConcreteStateA wants to change the state of the context.Context: Transition to ConcreteStateB.ConcreteStateB handles request2.ConcreteStateB wants to change the state of the context.Context: Transition to ConcreteStateA.

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