Angular2：在可观察的内部更改检测

Question

我刚用Angular2 RC3尝试了我的第一个应用程序（使用Angular-CLI），我迷失了...

我对变量word “更改检测”有word 。 我更新了Observable的subscribe方法中的word变量，但没有检测到任何变化。

app.component.ts

import { Component, Inject, OnInit } from '@angular/core';
import { VoiceRecognitionService } from './voice-recognition.service';

@Component({
  moduleId: module.id,
  selector: 'app-root',
  template: `<h1>{{word}}</h1>`, // => No prints any update
  providers: [VoiceRecognitionService],
  styleUrls: ['app.component.css']
})
export class AppComponent implements OnInit {

  private voice: VoiceRecognitionService;
  public word: string = '';

  constructor( @Inject(VoiceRecognitionService) voiceRecognition: VoiceRecognitionService) {
    this.voice = voiceRecognition;
  }

  ngOnInit() {
    this.voice.record('ca')
      .subscribe(word => {
        console.log(word); // => Is printing well the new word
        this.word = `${word}...`; // => No changes detected
      });
  }
}

我记得在Angular 1中使用$scope.$apply于类似的情况，我搜索相同的Angular2，我找到了NgZone.run ，我试图在NgZone.run执行，但没有。

我做错了什么？

非常感谢。

---

额外：

我与Observable分享我的服务：

语音recognition.service.ts

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Rx';

export interface IWindow extends Window {
  webkitSpeechRecognition: any;
}

@Injectable()
export class VoiceRecognitionService {

  constructor() {
    /* void */
  }

  /**
   * Record
   * @param {string} language - Language of the voice recognition
   * @returns {Observable<string>} - Observable of voice converted to string 
   */
  record(language: string): Observable<string> {
    return Observable.create((observer) => {
      const { webkitSpeechRecognition }: IWindow = <IWindow>window;
      const recognition = new webkitSpeechRecognition();

      recognition.onresult = (e) => observer.next(e.results.item(e.results.length - 1).item(0).transcript);
      recognition.onerror = observer.error;
      recognition.onend = observer.completed;

      recognition.continuous = true;
      recognition.interimResults = true;
      recognition.lang = language;
      recognition.start();
    });
  }
}

Answer 1

我假设Angulars区域没有修补webkitSpeechRecognition API。

要解决此问题，请使用zone.run(...)强制执行返回Angulars区域：

@Injectable()
export class VoiceRecognitionService {

  constructor(private zone:NgZone) {
    /* void */
  }

  /**
   * Record
   * @param {string} language - Language of the voice recognition
   * @returns {Observable<string>} - Observable of voice converted to string 
   */
  record(language: string): Observable<string> {
    return Observable.create((observer) => {
      const { webkitSpeechRecognition }: IWindow = <IWindow>window;
      const recognition = new webkitSpeechRecognition();

      recognition.onresult = (e) => this.zone.run(() => observer.next(e.results.item(e.results.length - 1).item(0).transcript));
      recognition.onerror = (e) => this.zone.run(() => observer.error(e));
      recognition.onend = (e) => this.zone.run(() => observer.completed(e));

      recognition.continuous = true;
      recognition.interimResults = true;
      recognition.lang = language;
      recognition.start();
    });
  }
}

如果回调需要不同数量的参数（ (e) ），请相应地调整代码。 我只假设了一个参数。

这种方法的优点是该服务的用户不必采取额外措施。

Answer 2

你最终可能会显式调用的detectChanges的方法ChangeDetectorRef类：

constructor( @Inject(VoiceRecognitionService) voiceRecognition: VoiceRecognitionService,
    private cdr:ChangeDetectorRef) {
  this.voice = voiceRecognition;
}

ngOnInit() {
  this.voice.record('ca')
    .subscribe(word => {
      console.log(word); // => Is printing well the new word
      this.word = `${word}...`; // => No changes detected
      this.cdr.detectChanges(); // <---------
    });
}