php框架的设计模式

class Database {
    private static $instance = null;

    public static function getInstance() {
        if (self::$instance === null) {
            self::$instance = new Database();
        }

        return self::$instance;
    }

    private function __construct() {}
}

$db = Database::getInstance();
$db->connect();

interface Shape {
    public function draw();
}

class Circle implements Shape {
    public function draw() {
        echo '绘制一个圆形' . PHP_EOL;
    }
}

class ShapeDecorator implements Shape {
    protected $shape;

    public function __construct(Shape $shape) {
        $this->shape = $shape;
    }

    public function draw() {
        $this->shape->draw();
    }
}

class ColoredShapeDecorator extends ShapeDecorator {
    public function draw() {
        parent::draw();
        echo '用红色填充' . PHP_EOL;
    }
}

$circle = new Circle();
$coloredCircle = new ColoredShapeDecorator($circle);
$coloredCircle->draw();

interface Subject {
    public function attach(Observer $observer);
    public function detach(Observer $observer);
    public function notify();
}

interface Observer {
    public function update(Subject $subject);
}

class ConcreteSubject implements Subject {
    private $observers = [];

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

    public function detach(Observer $observer) {
        $index = array_search($observer, $this->observers);
        if ($index !== false) {
            unset($this->observers[$index]);
        }
    }

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

class ConcreteObserver implements Observer {
    public function update(Subject $subject) {
        echo 'Observer notified of state change' . PHP_EOL;
    }
}

$subject = new ConcreteSubject();
$observer = new ConcreteObserver();
$subject->attach($observer);

// 观察者监听来自主题的通知
$subject->notify();