PHP Design Patterns: for object-oriented solutions

PHP design patterns provide general solutions to deal with common software design problems, improving code scalability, maintainability and flexibility. Common PHP design patterns include: Strategy pattern: allows dynamic switching of algorithms to adapt to different strategies. Singleton mode: Ensure that the class has only one instance for global access. Observer Pattern: Allows objects to subscribe to events to receive notifications when their state changes.

PHP Design Patterns: Solutions for Object-Oriented Programming

Introduction

Design patterns are general solutions to common software design problems that have been solved. In PHP, they are widely used to improve code scalability, maintainability, and flexibility. This tutorial will introduce some of the most common PHP design patterns and demonstrate them through practical examples.

Strategy Mode

Strategy mode allows you to define a series of algorithms and then switch them dynamically. This allows the code to flexibly adapt to different strategies without modifying its core logic.

Practical case:

Suppose we have a file upload system that needs to support multiple upload strategies, such as local storage and cloud storage. We can use the strategy pattern to separate the specific implementation of the upload strategy:

interface UploadStrategy
{
    public function upload($file);
}

class LocalUploadStrategy implements UploadStrategy
{
    public function upload($file)
    {
        // 本地存储代码
    }
}

class CloudUploadStrategy implements UploadStrategy
{
    public function upload($file)
    {
        // 云存储代码
    }
}

class FileUploader
{
    private $uploadStrategy;

    public function __construct(UploadStrategy $uploadStrategy)
    {
        $this->uploadStrategy = $uploadStrategy;
    }

    public function upload($file)
    {
        $this->uploadStrategy->upload($file);
    }
}

In this example, we can instantiate different upload strategies as needed and pass them to the FileUploader class.

Singleton pattern

The singleton pattern ensures that a class has only one instance. This is useful in situations where global access to a single object is required.

Practical case:

For example, we may have a database connection class, and we only want to create a single instance:

class DatabaseConnection
{
    private static $instance;

    private function __construct()
    {
        // 数据库连接逻辑
    }

    public static function getInstance()
    {
        if (!isset(self::$instance)) {
            self::$instance = new DatabaseConnection();
        }

        return self::$instance;
    }
}

In this way, no matter Whenever the getInstance() method is called, we will all get the same database connection instance.

Observer Pattern

The Observer pattern allows one object to subscribe to the events of another object, and when the latter changes, it will receive notifications. This is useful for loosely coupled systems where multiple objects need to react to the same event.

Practical case:

Suppose we have a news website where users can subscribe to news categories of interest. We can use the Observer pattern to notify users when new news is available:

interface NewsSubject
{
    public function attach(NewsObserver $observer);
    public function detach(NewsObserver $observer);
    public function notify();
}

interface NewsObserver
{
    public function update();
}

class News implements NewsSubject
{
    private $observers = [];

    public function attach(NewsObserver $observer)
    {
        $this->observers[] = $observer;
    }

    public function detach(NewsObserver $observer)
    {
        unset($this->observers[array_search($observer, $this->observers)]);
    }

    public function notify()
    {
        foreach ($this->observers as $observer) {
            $observer->update();
        }
    }

    public function publishNews()
    {
        // 新闻发布逻辑
        $this->notify();
    }
}

class EmailObserver implements NewsObserver
{
    public function update()
    {
        // 发送电子邮件通知
    }
}

class SMSObserver implements NewsObserver
{
    public function update()
    {
        // 发送短信通知
    }
}

Using this design pattern, the News object will notify its subscribers (e.g. e-mail) when new news is released. Email and SMS Watcher).

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