Question

我尝试使用Observable和ChangeDetectionStrategy来通知其他组件有关更改的信息。不幸的是，Observable对象addItemStream未定义。这有什么不对？

import { Component, ChangeDetectionStrategy, ChangeDetectorRef, Input }          from '@angular/core'
import { ROUTER_DIRECTIVES, Router }  from '@angular/router';
import {Observable} from 'rxjs/Observable';

@Component({
    selector: 'bp-header',
    templateUrl: 'app/header.component.html',
    directives: [ROUTER_DIRECTIVES],
    changeDetection: ChangeDetectionStrategy.OnPush
})
export class HeaderComponent {
    @Input() addItemStream: Observable<any>;
    public isActive: number;
    public language: string = "en";
    constructor(private cd: ChangeDetectorRef) {}
    ngOnInit() {
        this.isActive = 1;
     }
    ngAfterViewInit() {
    this.addItemStream.subscribe(() => {
        this.setLanguage; // application state changed
        this.cd.markForCheck();
       })
    }
    public setLanguage = (language: string) => {
        if (this.language === language) { return }
        else { this.language = language };
    }
    public setActive(active: number) {
        if (this.isActive === active) return;
        this.isActive = active;
    }
}

Answer 1

您正在订阅Observable中的ngOnInit。由于它是Input，Observable（以及所有其他Inputs）此时将为undefined。

尝试在ngAfterViewInit订阅它。或者，提供服务。这使你的生活（和分享Observable）变得更加容易。

Answer 2

您订阅它的位置并不重要。我通常在构造函数中执行此操作。但是，当组件初始化时，流是未定义的，所以只需在构造函数中初始化它：

constructor(private cd: ChangeDetectorRef) {
  this.addItemStream = new Observable<any>();
}

Angular 2. Observable未定义

2 个答案: