如何在 Angular 2 中创建可观察对象

Question

我正在尝试评估 Angular 2，但我遇到了 observables 的问题。

我正在尝试创建一个简单的服务，该服务最初返回一个硬编码数组，但最终会从 Web 服务中获取数据。

但是，我无法让它构建正常。

有什么想法吗？

export class FleetListService {

  private data: Observable<Array<IFleet>>;

  constructor() { }

  fleets: IFleet[] = JSON.parse( `[{ "id": 1, "name": "John", "description": "John has been in the Audio/Video industry since 1990. He has led DevAv as its CEO since 2003. When not working hard as the CEO, John loves to golf and bowl. He once bowled a perfect game of 300.", "childCount": 5, "isUsed": true }, 
                                   { "id": 2, "name": "Olivia", "description": "Olivia loves to sell. She has been selling DevAV products since 2012. Olivia was homecoming queen in high school. She is expecting her first child in 6 months. Good Luck Olivia.", "childCount": 5 }, 
                                   { "id": 3, "name": "Robert", "description": "Robert was recently voted the CMO of the year by CMO Magazine. He is a proud member of the DevAV Management Team. Robert is a championship BBQ chef, so when you get the chance ask him for his secret recipe.", "childCount": 4 }, 
                                   { "id": 4, "name": "Greta", "description": "Greta has been DevAV's HR Manager since 2003. She joined DevAV from Sonee Corp.  Greta is currently training for the NYC marathon. Her best marathon time is 4 hours. Go Greta.", "childCount": 11 }, 
                                   { "id": 5, "name": "Brett", "description": "Brett came to DevAv from Microsoft and has led our IT department since 2012.  When he is not working hard for DevAV, he coaches Little League (he was a high school pitcher).", "childCount": 13 }, 
                                   { "id": 6, "name": "Sandra", "description": "Sandra is a CPA and has been our controller since 2008. She loves to interact with staff so if you've not met her, be certain to say hi.  Sandra has 2 daughters both of whom are accomplished gymnasts.", "childCount": 44 }, 
                                   { "id": 7, "name": "Kevin", "description": "Kevin is our hard-working shipping manager and has been helping that department work like clockwork for 18 months.  When not in the office, he is usually on the basketball court playing pick-up games.", "childCount": 5 }, 
                                   { "id": 8, "name": "Cynthia", "description": "Cindy joined us in 2008 and has been in the HR department for 2 years.   She was recently awarded employee of the month. Way to go Cindy!", "childCount": 4 }, 
                                   { "id": 9, "name": "Kent", "description": "As our ombudsman, Kent is on the front-lines solving customer problems and helping our partners address issues out in the field.    He is a classically trained musician and is a member of the Chamber Orchestra.", "childCount": 26 }, 
                                   { "id": 10, "name": "Taylor", "description": "If you are like the rest of us at DevAV, then you've probably reached out for help from Taylor. He does a great job as a member of our IT department.", "childCount": 5 }, 
                                   { "id": 11, "name": "Sam", "description": "Sammy is proud to be a member of the DevAV team. He joined the team in 2012 and has been in the sales department from the beginning.  He has just picked up golf so you can find him on the links every weekend.", "childCount": 11 }, 
                                   { "id": 12, "name": "Kelly", "description": "Kelly loves people and that's why she joined DevAV's support department. One of the funniest people in the company, she does stand-up on the weekends at the Laugh Factory.", "childCount": 5 }, 
                                   { "id": 13, "name": "Natalie", "description": "Natalie travels the US and teaches our partners how to explain the benefits of our products to customers.  She is a proud wife and mom and volunteers her time at the elementary school.", "childCount": 29 }, 
                                   { "id": 14, "name": "Walter", "description": "Walter has been developing apps and websites for DevAV since 2011. His passion is software and if you ever walk by his desk, you'll know why.  Wally once worked 72 hours straight - writing code and fixing bugs.", "childCount": 13 }]`);

  getFleets(): Observable<IFleet[]> {
    return new Observable((data : IFleet[]) => {
      return this.fleets;
    }
  }
}

Answer 1

你可以使用 Observable.of 方法。

getFleets(): Observable<IFleet[]> {
     return Observable.of(this.fleet)
}

不要忘记使用以下行导入

   import "rxjs/add/observable/of";  // For RxJs  5.0+

对于 RxJS 6.x

getFleets(): Observable<IFleet[]> {
         return of(this.fleet)
    }

“of”的导入语句

import { of } from "rxjs";

Answer 2

这有点晚了，无论如何只是为了澄清。如果您想模仿自己的类似承诺，这就是您如何创建一个简单的可观察对象的方法。你会的

let observable=Observable.create(observer => {
      setTimeout(() => {
        observer.next("data to send can be object or anything");
        console.log("am done");
        observer.complete(); // to show we are done with our processing
       // observer.error(new Error("error message"));
      }, 2000);

    })

订阅很简单

observable.subscribe((data) => {
console.log(data); // should be 'data to send can be object or anything'
});

您也可以使用toPromise() or fromPromise(observable) 运算符等将其转换为promise。

Answer 3

为此，您可以使用 BehaviorSubject

export class FleetListService {
    public data: any = new BehaviorSubject('your hard coded data goes here');
    getdata() {
        //do your stuff
        this.FleetListService.next('new data got from server');
    }
}

Subject 的变体之一是 BehaviorSubject，它具有“当前值”的概念。它存储发送给其消费者的最新值，并且每当有新的观察者订阅时，它将立即从 BehaviorSubject 接收“当前值”。 行为主体总是返回最后一个数据。更多info