RxJS之Subject主题 ( Angular环境 )

一 Subject主题

Subject是Observable的子类。- Subject是多播的，允许将值多播给多个观察者。普通的 Observable 是单播的。

在 Subject 的内部，subscribe 不会调用发送值的新执行。它只是将给定的观察者注册到观察者列表中，类似于其他库或语言中的 addListener 的工作方式。

要给 Subject 提供新值，只要调用 next(theValue)，它会将值多播给已注册监听该 Subject 的观察者们。

1import { Component, OnInit } from '@angular/core';
2import { Subject } from 'rxjs/Subject';
3import { Subscription } from 'rxjs/Subscription';
4
5@Component({
6  selector: 'app-subject',
7  templateUrl: './subject.component.html',
8  styleUrls: ['./subject.component.css']
9})
10export class SubjectComponent implements OnInit {
11
12  constructor() { }
13
14  ngOnInit() {
15    const subject: Subject<string> = new Subject<string>();
16    const subscriptionA: Subscription = subject.subscribe(
17      (val: string) => {
18        console.log(`observerA: ${val}`);
19      }
20    );
21    const subscriptionB: Subscription = subject.subscribe(
22      (val: string) => {
23        console.log(`observerB: ${val}`);
24      }
25    );
26    subject.next('Mikey');
27    subject.next('Leo');
28    subscriptionA.unsubscribe(); // 取消订阅
29    subscriptionB.unsubscribe(); // 取消订阅
30    subject.next('Raph');
31    subject.complete();
32  }
33
34}

每个 Subject 都是观察者。 - Subject 是一个有如下方法的对象： next(v)、error(e) 和 complete() ，可以把 Subject 作为参数传给任何 Observable 的 subscribe 方法。

1import { Component, OnInit } from '@angular/core';
2import { Subject } from 'rxjs/Subject';
3import { Subscription } from 'rxjs/Subscription';
4import { from } from 'rxjs/observable/from';
5import { Observable } from 'rxjs/Observable';
6
7@Component({
8  selector: 'app-subject',
9  templateUrl: './subject.component.html',
10  styleUrls: ['./subject.component.css']
11})
12export class SubjectComponent implements OnInit {
13
14  constructor() { }
15
16  ngOnInit() {
17    const subject: Subject<string> = new Subject<string>();
18    const subscriptionA: Subscription = subject.subscribe(
19      (val: string) => {
20        console.log(`observerA: ${val}`);
21      }
22    );
23    const subscriptionB: Subscription = subject.subscribe(
24      (val: string) => {
25        console.log(`observerB: ${val}`);
26      }
27    );
28
29    const observable: Observable<string> = from(['Raph', 'Don']);
30    observable.subscribe(subject);
31
32  }
33
34}