如何每隔一段时间发出HTTP请求？

Question

我对 angular 和 rxjs 还很陌生。我正在尝试创建一个 angular2 应用程序，它从静态服务的文本文件（在服务器本地）获取一些数据，我想在固定时间使用 Angular2 的 http 提供程序和 rxjs 的映射检索并映射到 Datamodel interval(5000)。反映对提供的 txt 文件的任何更改。

使用 rxjs 4.x 我知道你可以使用 Observable.interval(5000) 来完成这项工作，但它似乎不存在于 rxjs 5 中。我的解决方法目前使用 <meta http-equiv="refresh" content="5" > 刷新整个应用程序，这会重新加载整个页面，从而重新加载数据。

所以我真正想要的是使用可观察对象执行此操作的某种方法，也许可以检查是否发生了任何更改。或者只是重新加载数据。

任何帮助或other/better方式将不胜感激。

我目前拥有的：

@Injectable()
export class DataService {

    constructor(private http:Http){}

    getData(url) {
        return this.http.get(url)
            .map(res => {
                return res.text();
            })
            .map(res => {
                return res.split("\n");
            })
            .map(res => {
                var dataModels: DataModel[] = [];
                res.forEach(str => {
                    var s = str.split(",");
                    if(s[0] !== "") {
                        dataModels.push(new DataModel(s[0], parseInt(s[1]), parseInt(s[2])));
                    }
                });
                return dataModels;
            })
    }
}

@Component({
selector: 'my-app',
template: `Some html to display the data`,
providers: [DataService],
export class AppComponent {

data:DataModel[];

constructor(dataService:DataService) {}

ngOnInit() {
    this.dataService.getData('url').subscribe(
        res => {
            this.data= res;

        },
        err => console.log(err),
        () => console.log("Data received")
        );
    }
}

依赖关系：package.json

"dependencies": {
  "angular2": "^2.0.0-beta.3",
  "bootstrap": "^4.0.0-alpha.2",
  "es6-promise": "^3.0.2",
  "es6-shim": "^0.33.13",
  "jquery": "^2.2.0",
  "reflect-metadata": "^0.1.2",
  "rxjs": "^5.0.0-beta.0",
  "systemjs": "^0.19.20",
  "zone.js": "^0.5.11"
},
"devDependencies": {
  "typescript": "^1.7.5"
}

index.html 进口：

<script src="node_modules/es6-shim/es6-shim.min.js"></script>
<script src="node_modules/systemjs/dist/system-polyfills.js"></script>

<script src="node_modules/angular2/bundles/angular2-polyfills.js"></script>
<script src="node_modules/systemjs/dist/system.src.js"></script>
<script src="node_modules/rxjs/bundles/Rx.js"></script>
<script src="node_modules/angular2/bundles/angular2.dev.js"></script>
<script src="node_modules/angular2/bundles/router.dev.js"></script>
<script src="node_modules/angular2/bundles/http.dev.js"></script>

Answer 1

您可以在 Angular2 中使用 Observable 的 interval 方法。

import {Component,Input} from 'angular2/core';
import {Observable} from 'rxjs/Rx';

@Component({
  selector: 'my-app',
  template: `
    <div>
      {{message}}
    </div>
  `
})
export class AppComponent {
  constructor() {
    Observable.interval(500)
          .take(10).map((x) => x+1)
          .subscribe((x) => {
            this.message = x;
          }):
  }
}

这是相应的 plunkr 描述：https://plnkr.co/edit/pVMEbbGSzMwSBS4XEXJI?p=preview.

基于此，您可以插入您的 HTTP 请求：

initializePolling() {
  return Observable
     .interval(60000)
     .flatMap(() => {
       return this.dataService.getData('url'));
     });
}

Answer 2

对于带有 rxjs@5.0.0（回答时的 beta.6）的 TypeScript（回答时为 1.8.10）/angular2（回答时为 rc1），您需要使用 IntervalObservable它扩展了 Observable class

import {IntervalObservable} from 'rxjs/observable/IntervalObservable'

IntervalObservable.create(5000).take(10).map((x) => x + 1)

Answer 3

由于 rxjs/observable 最近的变化，我认为这个答案不再有效您现在必须使用 IntervalObservable。

https://github.com/ReactiveX/rxjs/blob/master/src/observable/IntervalObservable.ts

import { IntervalObservable } from 'rxjs/observable/IntervalObservable';

@Component({
  ...
})
export class AppComponent {
  n: number = 0;
  constructor() {
    IntervalObservable.create(1000).subscribe(n => this.n = n);
  }
}

Answer 4

正如@Adam 和@Ploppy 所提到的，Observable.interval() 现在 ~~已弃用~~ 不是创建此类可观察对象的首选方式。执行此操作的首选方法是通过 IntervalObservable 或 TimerObservable。 [目前在 Typscript 2.5.2，rxjs 5.4.3，Angular 4.0.0]

我想在此答案中添加一些用法，以展示我在 Angular 2 框架中找到的最佳方法。

首先是您的服务（通过“ng g service MyExample”命令在 angular cli 中创建）。假设服务是 RESTful（http get request returns a json):

我的-example.service.ts

import { Injectable } from '@angular/core';
import { Http, Response} from "@angular/http";
import { MyDataModel } from "./my-data-model";
import { Observable } from "rxjs";
import 'rxjs/Rx';

@Injectable()
export class MyExampleService {
  private url = 'http://localhost:3000'; // full uri of the service to consume here

  constructor(private http: Http) { }

  get(): Observable<MyDataModel>{
    return this.http
      .get(this.url)
      .map((res: Response) => res.json());
  }
}

*** 查看 Angular 5 ***

服务的底部更新

现在你的组件代码 ('ng g component MyExample'):

我的-example.component.ts:

import { Component, OnDestroy, OnInit } from '@angular/core';
import { MyDataModel } from "../my-data-model";
import { MyExampleService } from "../my-example.service";
import { Observable } from "rxjs";
import { IntervalObservable } from "rxjs/observable/IntervalObservable";
import 'rxjs/add/operator/takeWhile';

@Component({
  selector: 'app-my-example',
  templateUrl: './my-example.component.html',
  styleUrls: ['./my-example.component.css']
})
export class MyExampleComponent implements OnInit, OnDestroy {
  private data: MyDataModel;
  private display: boolean; // whether to display info in the component
                            // use *ngIf="display" in your html to take
                            // advantage of this

  private alive: boolean; // used to unsubscribe from the IntervalObservable
                          // when OnDestroy is called.

  constructor(private myExampleService: MyExampleService) {
    this.display = false;
    this.alive = true;
  }

  ngOnInit() {
    // get our data immediately when the component inits
    this.myExampleService.get()
      .first() // only gets fired once
      .subscribe((data) => {
        this.data = data;
        this.display = true;
      });

    // get our data every subsequent 10 seconds
    IntervalObservable.create(10000)
      .takeWhile(() => this.alive) // only fires when component is alive
      .subscribe(() => {
        this.myExampleService.get()
          .subscribe(data => {
            this.data = data;
          });
      });
  }

  ngOnDestroy(){
    this.alive = false; // switches your IntervalObservable off
  }
}

===编辑===

更新了组件 ts 代码以通过 TimerObservable 整合订阅：

import { Component, OnDestroy, OnInit } from '@angular/core';
import { MyDataModel } from "../my-data-model";
import { MyExampleService } from "../my-example.service";
import { Observable } from "rxjs";
import { TimerObservable } from "rxjs/observable/TimerObservable";
import 'rxjs/add/operator/takeWhile';

@Component({
  selector: 'app-my-example',
  templateUrl: './my-example.component.html',
  styleUrls: ['./my-example.component.css']
})
export class MyExampleComponent implements OnInit, OnDestroy {
  private data: MyDataModel;
  private display: boolean; // whether to display info in the component
                            // use *ngIf="display" in your html to take
                            // advantage of this

  private alive: boolean; // used to unsubscribe from the TimerObservable
                          // when OnDestroy is called.
  private interval: number;

  constructor(private myExampleService: MyExampleService) {
    this.display = false;
    this.alive = true;
    this.interval = 10000;
  }

  ngOnInit() {
    TimerObservable.create(0, this.interval)
      .takeWhile(() => this.alive)
      .subscribe(() => {
        this.myExampleService.get()
          .subscribe((data) => {
            this.data = data;
            if(!this.display){
              this.display = true;
            }
          });
      });
  }

  ngOnDestroy(){
    this.alive = false; // switches your TimerObservable off
  }
}

===编辑===

my-example-service.ts（使用 HttpClient a la Angular 5）：

import { Injectable } from '@angular/core';
import { HttpClient} from "@angular/common/http";
import { MyDataModel } from "./my-data-model";
import { Observable } from "rxjs";
import 'rxjs/Rx';

@Injectable()
export class MyExampleService {
  private url = 'http://localhost:3000'; // full uri of the service to consume here

  constructor(private http: HttpClient) { }

  get(): Observable<MyDataModel>{
    return this.http
      .get<MyDataModel>(this.url);
  }
}

注意更改为使用 HttpClient 而不是 Http（在 angular5 中已弃用）和 get 方法，该方法允许将响应解析到我们的数据模型中，而无需使用 rxjs .map() 运算符。虽然 angular5 的服务发生变化，但组件代码保持不变。

Answer 5

这可以通过 switchMap

轻松完成

Observable.timer(0, 5000)
          .switchMap((t) =>
            this.http.get(...).pipe(
                catchError(...)
            )
          )
          .subscribe(...)

Answer 6

Disaclaimer: this was originaly an edit for another answer, but contains too many changes.

这可以通过 switchMap 轻松完成：

Observable.timer(0, 5000)
  .switchMap(() => this.http.get(...).pipe(...)
  .subscribe(...)

或者在 RxJS 6 语法中：

import { timer } from 'rxjs';
import { switchMap } from 'rxjs/operators';

timer(0, 5000) // repeats every 5 seconds
  .pipe(switchMap(() => this.http.get(...).pipe(...))
  .subscribe(...);

您甚至可以使用 interval 而不是 timer:

import { interval } from 'rxjs';
import { switchMap } from 'rxjs/operators';

interval(5000) // repeats every 5 seconds
  .pipe(switchMap(() => this.http.get(...).pipe(...))
  .subscribe(...);

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