typescript – 从(服务器发送的)EventSource创建RxJS Observable

发布时间：2020-12-17 06:48:25 所属栏目：安全来源：网络整理

导读：我想从EventSource(服务器发送事件)创建一个RxJs Observable. 我尝试了以下方法： import {Component,OnInit} from 'angular2/core';import {Subject,Observable} from 'rxjs/Rx';@Component({ selector: 'my-app',template: `h1My second Angular 2 App/h1

我想从EventSource(服务器发送事件)创建一个RxJs Observable.

我尝试了以下方法：

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

@Component({
    selector: 'my-app',template: `<h1>My second Angular 2 App</h1>
    <ul>
        <li *ngFor="#s of someStrings">
           a string: {{ s }}
        </li>
    </ul>
    `
})
export class AppComponent implements OnInit {

    someStrings:string[] = [];

    ngOnInit() {
        let eventSource = new EventSource('/interval-sse-observable');
        let observable = Observable.create(eventSource);
        observable.subscribe({
            next: aString => this.someStrings.push(aString.data),error: err => console.error('something wrong occurred: ' + err)
        });
    }
}

但我得到以下异常：

EXCEPTION: Error: Uncaught (in promise): EXCEPTION: TypeError: this._subscribe is not a function in [null]
ORIGINAL EXCEPTION: TypeError: this._subscribe is not a function
ORIGINAL STACKTRACE:
TypeError: this._subscribe is not a function
    at Observable.subscribe (https://cdnjs.cloudflare.com/ajax/libs/angular.js/2.0.0-beta.15/Rx.js:11210:29)
    at AppComponent.ngOnInit (http://localhost:8080/scripts/app.component.ts!transpiled:30:28)
    at AbstractChangeDetector.ChangeDetector_HostAppComponent_0.detectChangesInRecordsInternal (viewFactory_HostAppComponent:21:99)
    at AbstractChangeDetector.detectChangesInRecords (https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:9689:14)
    at AbstractChangeDetector.runDetectChanges (https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:9672:12)
    at AbstractChangeDetector.detectChanges (https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:9661:12)
    at ChangeDetectorRef_.detectChanges (https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:5280:16)
    at https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:13048:27
    at Array.forEach (native)
    at ApplicationRef_.tick (https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:13047:34)

为了完整起见,这是我的index.html的内容：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>sse demo</title>
    <!-- 1. Load libraries -->
    <script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/2.0.0-beta.15/angular2-polyfills.js"></script>
    <script src="https://code.angularjs.org/tools/system.js"></script>
    <script src="https://code.angularjs.org/tools/typescript.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/2.0.0-beta.15/Rx.js"></script>
    <script src="https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/2.0.0-beta.15/http.dev.js"></script>

    <!-- 2. Configure SystemJS -->
    <script>
        System.config({
            transpiler: 'typescript',typescriptOptions: { emitDecoratorMetadata: true }
        });
        System.import('./scripts/app.ts')
                .then(null,console.error.bind(console));
    </script>
</head>
<body>

<my-app>Loading...</my-app>

</body>
</html>

有人可以帮忙吗？

编辑1：按照Yurzui的建议,我修改了我的代码如下：

ngOnInit() {
    let observable = Observable.create(observer => {
        const eventSource = new EventSource('/interval-sse-observable');
        eventSource.onmessage = x => observer.next(console.log(x));
        eventSource.onerror = x => observer.error(console.log('EventSource failed'));

        return () => {
            eventSource.close();
        };
    });
    observable.subscribe({
        next: aString => this.someStrings.push(aString.data),error: err => console.error('something wrong occurred: ' + err)
    });
}

它会在控制台中记录第一条消息,如下所示：

MessageEvent {isTrusted: true,data: "c374a15b-b37d-498e-8ab0-49643b79c1bb",origin: "http://localhost:8080",lastEventId: "",source: null…}bubbles: falsecancelBubble: falsecancelable: falsecurrentTarget: EventSourcedata: "c374a15b-b37d-498e-8ab0-49643b79c1bb"defaultPrevented: falseeventPhase: 0isTrusted: trueisTrusted: truelastEventId: ""origin: "http://localhost:8080"path: Array[0]ports: nullreturnValue: truesource: nullsrcElement: EventSourcetarget: EventSourcetimeStamp: 6257.125type: "message"__proto__: MessageEvent
Rx.js:10982 Uncaught TypeError: Cannot read property 'data' of undefinedSystem.register.exports_1.execute.AppComponent.ngOnInit.observable.subscribe.next @ app.component.ts:29SafeSubscriber.__tryOrUnsub @ Rx.js:10979SafeSubscriber.next @ Rx.js:10934Subscriber._next @ Rx.js:10894Subscriber.next @ Rx.js:10871System.register.exports_1.execute.AppComponent.ngOnInit.Rx_1.Observable.create.eventSource.onmessage @ app.component.ts:21

现在,如果不是在控制台中记录x变量,我只需将其传递给下一个方法,如下所示：

eventSource.onmessage = x => observer.next(x);

服务器发送的事件由客户端检索(我在chrome dev工具中看到它们),但模板中没有显示任何字符串数组未填充…

顺便说一句,我必须删除JSON.parse(x.data),因为它导致错误.

解决方法

您可以使用以下代码手动为EventSource流创建Observable：

export class AppComponent implements OnInit {
  someStrings:string[] = [];

  constructor(private zone: NgZone) {}

  ngOnInit(){
    const observable = Observable.create(observer => {
      const eventSource = new EventSource('/interval-sse-observable');
      eventSource.onmessage = x => observer.next(x.data);
      eventSource.onerror = x => observer.error(x);

      return () => {
        eventSource.close();
      };
    });

    this.subscription = observable.subscribe({
      next: guid => {
        this.zone.run(() => this.someStrings.push(guid));
      },error: err => console.error('something wrong occurred: ' + err)
    });
  }
}

// somewhere
// this.subscription.unsubscribe()

不要忘记导入NgZone类：

import {Component,OnInit,NgZone} from '@angular/core';

另见Angular2 View Not Changing After Data Is Updated

（编辑：李大同）

【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容!