typescript: Observer Pattern

 

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/**  * Observer Pattern 观察者是一种行为设计模式， 允许一个对象将其状态的改变通知其他对象  * file: Observerts.ts  * The Subject interface declares a set of methods for managing subscribers.  */ interface GeovinSubject {       // Attach an observer to the subject.     attach(observer: Observer):string ; //void       // Detach an observer from the subject.     detach(observer: Observer):string ; //void       // Notify all observers about an event.     notify(): string; //void }   /**  * The Subject owns some important state and notifies observers when the state  * changes.  */ class ConcreteSubject implements GeovinSubject {     /**      * @type {number} For the sake of simplicity, the Subject's state, essential      * to all subscribers, is stored in this variable.      */     public state: number;       /**      * @type {Observer[]} List of subscribers. In real life, the list of      * subscribers can be stored more comprehensively (categorized by event      * type, etc.).      */     private observers: Observer[] = [];       /**      * The subscription management methods.      */     public attach(observer: Observer): string { //void         const isExist = this.observers.includes(observer);  //es2016 later         if (isExist) {             // console.log('Subject: Observer has been attached already.');             return "Subject: Observer has been attached already.";         }           console.log('Subject: Attached an observer.');         this.observers.push(observer);         return "Subject: Attached an observer.";     }       public detach(observer: Observer): string {         const observerIndex = this.observers.indexOf(observer);         if (observerIndex === -1) {             console.log('Subject: Nonexistent observer.');             return "Subject: Nonexistent observer.";         }           this.observers.splice(observerIndex, 1);         console.log('Subject: Detached an observer.');         return "Subject: Detached an observer.";     }       /**      * Trigger an update in each subscriber.      */     public notify(): string {         let getstr="";         console.log('Subject: Notifying observers...');         for (const observer of this.observers) {             observer.update(this);             getstr=getstr+"Subject: Notifying observers...";         }         return getstr;     }       /**      * Usually, the subscription logic is only a fraction of what a Subject can      * really do. Subjects commonly hold some important business logic, that      * triggers a notification method whenever something important is about to      * happen (or after it).      */     public someBusinessLogic(): string { //void         let getstr="";         console.log('\nSubject: I\'m doing something important.');         this.state = Math.floor(Math.random() * (10 + 1));           getstr=getstr+this.state.toString();           console.log(`Subject: My state has just changed to: ${this.state}`);         getstr=getstr+this.notify();         return getstr;     } }   /**  * 接口  * The Observer interface declares the update method, used by subjects.  */ interface Observer {     // Receive update from subject.     update(subject: GeovinSubject): string; //void }   /**  * Concrete Observers react to the updates issued by the Subject they had been  * attached to.  */ class ConcreteObserverA implements Observer {       /**      *      * @param subject      * @returns      */     public update(subject: GeovinSubject): string { //void         if (subject instanceof ConcreteSubject && subject.state < 3) {             console.log('ConcreteObserverA: Reacted to the event.');             return "ConcreteObserverA: Reacted to the event.";         }     } }   /**  *  */ class ConcreteObserverB implements Observer {       /**      *      * @param subject      * @returns      */     public update(subject: GeovinSubject): string { //void           if (subject instanceof ConcreteSubject && (subject.state === 0 || subject.state >= 2)) {               console.log('ConcreteObserverB: Reacted to the event.');             return "ConcreteObserverB: Reacted to the event.";         }     } } //bing AI 生成的代码示例 // 定义被观察者接口 interface Observable {     // 添加观察者     addObserver(observer: DuObserver): void;     // 删除观察者     removeObserver(observer: DuObserver): void;     // 通知所有观察者     notifyObservers(): void;   }       // 定义观察者接口   interface DuObserver {     // 接收被观察者的通知     update(observable: Observable): void;   }       // 定义一个具体的被观察者类：温度计   class Thermometer implements Observable {     // 存储观察者列表     private observers: DuObserver[] = [];     // 存储温度值     private temperature: number;         // 添加观察者     public addObserver(observer: DuObserver): void {       this.observers.push(observer);       console.log("添加了一个观察者");     }         // 删除观察者     public removeObserver(observer: DuObserver): void {       const index = this.observers.indexOf(observer);       if (index > -1) {         this.observers.splice(index, 1);         console.log("删除了一个观察者");       }     }         // 通知所有观察者     public notifyObservers(): void {       for (const observer of this.observers) {         observer.update(this);       }       console.log("通知了所有观察者");     }         // 获取温度值     public getTemperature(): number {       return this.temperature;     }         // 设置温度值，并通知所有观察者     public setTemperature(temperature: number): void {       this.temperature = temperature;       console.log("温度变化了");       this.notifyObservers();     }   }       // 定义一个具体的观察者类：手机   class Phone implements DuObserver {     // 接收被观察者的通知，并打印温度值     public update(observable: Observable): void {       if (observable instanceof Thermometer) {         console.log("手机收到了温度变化的通知，温度是：" + observable.getTemperature());       }     }   }       // 定义一个具体的观察者类：电脑   class Computer implements DuObserver {     // 接收被观察者的通知，并打印温度值     public update(observable: Observable): void {       if (observable instanceof Thermometer) {         console.log("电脑收到了温度变化的通知，温度是：" + observable.getTemperature());       }     }   }       // 测试代码   const thermometer = new Thermometer(); // 创建一个温度计对象   const phone = new Phone(); // 创建一个手机对象   const computer = new Computer(); // 创建一个电脑对象       thermometer.addObserver(phone); // 让手机订阅温度计   thermometer.addObserver(computer); // 让电脑订阅温度计       thermometer.setTemperature(25); // 设置温度为25       thermometer.removeObserver(phone); // 让手机取消订阅       thermometer.setTemperature(30); // 设置温度为30     //ECMAScript 2023 //https://262.ecma-international.org/14.0/ //https://github.com/tc39/ecma262   let pubObserver1=""; let pubObserver2=""; let pubObserver3="Geovin Du"; let pubObserver4="geovindu";   /**  * The client code.  */   const subject = new ConcreteSubject();   const observer1 = new ConcreteObserverA(); pubObserver1=subject.attach(observer1);   const observer2 = new ConcreteObserverB(); subject.attach(observer2);   pubObserver2=subject.someBusinessLogic(); pubObserver3=subject.someBusinessLogic();   subject.detach(observer2);   pubObserver4=subject.someBusinessLogic();   let messageObserver: string = 'Hello World,This is a typescript!,涂聚文 Geovin Du.Web'; document.body.innerHTML = messageObserver+",<br/>one="+pubObserver1+",<br/>two="+pubObserver2+",<br/>three="+pubObserver3+",<br/>four="+pubObserver4+",<br/>TypeScript Observer Pattern 观察者模式";

　　

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