What is the state pattern in PHP? Learn it through examples

In the previous article "Let’s talk about the singleton mode in PHP" we introduced the singleton mode in PHP. The following article will take you to understand the state mode in PHP design pattern.

The state pattern is not very easy to understand literally. What does the status here mean? Save status? That's not the memo mode. In fact, the state here is the state of the class. By changing a certain state of the class, the class feels like a different class. It’s a bit hard to say, so let’s learn the concept first and then read it later.

Gof class diagram and explanation

GoF definition: Allows an object to change its behavior when its internal state changes. The object appears to have modified its class

GoF Class Diagram

Code Implementation

class Context
{
    private $state;
    public function SetState(State $state): void
    {
        $this->state = $state;
    }
    public function Request(): void
    {
        $this->state = $this->state->Handle();
    }
}

A context class can also be regarded as a target class, which has a state object inside it. When calling Request(), call the Handle() method of the status class. The purpose is that changes in the current context class state are controlled by the external state class.

interface State
{
    public function Handle(): State;
}

class ConcreteStateA implements State
{
    public function Handle(): State
    {
        echo '当前是A状态', PHP_EOL;
        return new ConcreteStateB();
    }
}

class ConcreteStateB implements State
{
    public function Handle(): State
    {
        echo '当前是B状态', PHP_EOL;
        return new ConcreteStateA();
    }
}

Abstract state interface and two concrete implementations. These two specific implementations are actually calling each other. The effect of the implementation is that every time the context class calls the Request() method, the internal state class changes to another state. It's like a switch that switches back and forth between on and off.

$c = new Context();
$stateA = new ConcreteStateA();
$c->SetState($stateA);
$c->Request();
$c->Request();
$c->Request();
$c->Request();

The implementation of the client instantiates the context object and sets the initial state, and then continuously calls the Request() object to realize the switch state switching.

• Do you see the way? Here, the state changes are encapsulated into the external implementation class. The state is not switched within the context or the target class.
• So what is the meaning of the state mode? This example of the default class diagram is too simple. In fact, the real purpose of the state pattern is to solve the complex if nesting problem. The complex if nesting conditions are put into the external state classes one by one for judgment. In the following examples We will see that
• applies to: the behavior of an object depends on its state, and it must change its behavior according to the state at run time; an operation contains a large number of multi-branch conditional statements, and these Branching depends on the state of the object;
• The characteristics of the state pattern are: it localizes the behavior related to a specific state; it makes state transitions explicit; State objects can be shared;
• Commonly found in order systems, membership systems, and OA systems, that is, there will be various status changes in the process, and the status pattern can be used for the overall design and architecture

We have customized our own shopping mall system in the mobile phone system, so you can conveniently place orders and purchase our products on your mobile phone. An order (Context) will have multiple states (State), such as unpaid, paid, order completed, order refunded, and a lot of states. We put these states in the corresponding state classes to implement. Different state classes will call the next action of the state. For example, after payment, wait for the receipt of the goods, and after the refund, wait for the buyer to fill in the logistics form. Wait, in this way, the state mode can be flexibly used in our mall! !

Full code: https://github.com/zhangyue0503/designpatterns-php/blob/master/22.state/source/state.php

Example

Usually there will be a membership system in shopping mall applications. Generally, the higher the level, the more discounts members can enjoy. At this time, the use of status mode can be very convenient. Easily get membership level discounts. Of course, the most important thing is that using the status mode, you can only add the corresponding member discount status subclass when you need to add or delete a membership level. No other business code needs to be changed, let’s take a look at the specific implementation!

Member Discount Picture

Full source code: https://github.com/zhangyue0503/designpatterns-php/ blob/master/22.state/source/state-member.php

<?php

class Member
{
    private $state;
    private $score;

    public function SetState($state)
    {
        $this->state = $state;
    }

    public function SetScore($score)
    {
        $this->score = $score;
    }

    public function GetScore()
    {
        return $this->score;
    }

    public function discount()
    {
        return $this->state->discount($this);
    }
}

interface State
{
    public function discount($member);
}

class PlatinumMemeberState implements State
{
    public function discount($member)
    {
        if ($member->GetScore() >= 1000) {
            return 0.80;
        } else {
            $member->SetState(new GoldMemberState());
            return $member->discount();
        }
    }
}

class GoldMemberState implements State
{
    public function discount($member)
    {
        if ($member->GetScore() >= 800) {
            return 0.85;
        } else {
            $member->SetState(new SilverMemberState());
            return $member->discount();
        }
    }
}

class SilverMemberState implements State
{
    public function discount($member)
    {
        if ($member->GetScore() >= 500) {
            return 0.90;
        } else {
            $member->SetState(new GeneralMemberState());
            return $member->discount();
        }
    }
}

class GeneralMemberState implements State
{
    public function discount($member)
    {
        return 0.95;
    }
}

$m = new Member();
$m->SetState(new PlatinumMemeberState());

$m->SetScore(1200);
echo &#39;当前会员&#39; . $m->GetScore() . &#39;积分，折扣为：&#39; . $m->discount(), PHP_EOL;

$m->SetScore(990);
echo &#39;当前会员&#39; . $m->GetScore() . &#39;积分，折扣为：&#39; . $m->discount(), PHP_EOL;

$m->SetScore(660);
echo &#39;当前会员&#39; . $m->GetScore() . &#39;积分，折扣为：&#39; . $m->discount(), PHP_EOL;

$m->SetScore(10);
echo &#39;当前会员&#39; . $m->GetScore() . &#39;积分，折扣为：&#39; . $m->discount(), PHP_EOL;

Description

• If you do not use the state mode, in Member In the discount() method, we may need to write many layers of if...else...judgment conditions
• At the same time, this also brings about the problem that the method experience is getting longer and longer, and it is becoming more and more difficult to maintain
• The state mode exists to solve this problem.
• When the result of the discount() behavior depends on the status of the Member object itself (membership points), the state mode is the best choice. , that is, the behavior of an object mentioned above depends on its state

Original address: https://juejin.cn/post/6844903991562731534

Author: Hardcore Project Manager

Recommended learning: "PHP Video Tutorial"

The above is the detailed content of What is the state pattern in PHP? Learn it through examples. For more information, please follow other related articles on the PHP Chinese website!