TypeError:无法读取属性' next'为null
import { NavService } from '../../providers/services/nav-service/nav-service';
@Component({
selector: 'ion-header',
providers: [NavService],
template: `
<ion-navbar>
<ion-title>{{navService.getCurrentName()}}</ion-title>
<ion-buttons start>
<button (click)="navService.goHome()">
<span primary showWhen="ios">Cancel</span>
<ion-icon name="md-close" showWhen="android,windows"></ion-icon>
</button>
</ion-buttons>
</ion-navbar>
`
})
import { Platform } from 'ionic-angular';
import { Observable } from 'rxjs/Observable';
import { Injectable, ViewChild } from '@angular/core'
@Injectable()
export class NavService {
private dismissObserver: any
public dismiss: any
constructor (
private authService: AuthService,
private platform: Platform
) {
this.dismissObserver = null;
this.dismiss = Observable.create(observer => {
this.dismissObserver = observer;
});
}
public goHome():void {
this.dismissObserver.next(true);
}
@Component({
providers: [NavService]
})
export class MyApp {
@ViewChild(Nav) navController: Nav
constructor(
public navService: NavService
) {
this.initializeApp()
}
initializeApp() {
this.platform.ready().then(() => {
StatusBar.styleDefault()
this.setRoot()
this.navController.setRoot(HomePage);
this.navService.dismiss.subscribe((event) => {
console.log ("event", event);
this.navController.setRoot(HomePage)
})
})
}
ionicBootstrap(MyApp, [])
顺便说一下,我正在使用这个&#34;教程&#34;:
答案 0 :(得分:6)
订阅Observable.create
时,会调用dismissObserver
中您分配dismiss
的代码。因此,如果您在该订阅之前调用goHome
,那么dismissObserver
在此时为空并且您收到错误
无论如何,您使用dismiss
和dismissObserver
实施的内容是Subject
的概念。只需将您的NavService构造函数和goHome
替换为:
constructor (
private authService: AuthService,
private platform: Platform
) {
this.dismiss = new Subject();
}
public goHome():void {
this.dismiss.next(true);
}
并且你很好:如果您的订阅在它之后,您可能会错过价值,但不会引发任何错误。尝试将Subject
替换为BehaviorSubject
,以便为发布后的订阅缓存一个值。
import { Subject } from 'rxjs/Subject';