关于后端:行为型设计模式状态-State

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。

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

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。

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.

本文由 mdnice 多平台公布

关于后端:行为型设计模式状态-State

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