获取以前的路线Angular 7

Question

我创建了一个小服务，可以在其中存储路线更改。

import { Injectable } from '@angular/core';
import { Router, NavigationEnd } from '@angular/router';

@Injectable()
export class RouteState {

  private previousUrl: string;
  private currentUrl: string;

  constructor(private router: Router) {
    this.currentUrl = this.router.url;
    router.events.subscribe(event => {
      if (event instanceof NavigationEnd) {        
        this.previousUrl = this.currentUrl;
        this.currentUrl = event.url;
      };
    });
  }

  public getPreviousUrl() {
    return this.previousUrl;
  }    
}

但是每次路由更改时，vars currentUrl和previousUrl都是未定义的。难道我做错了什么？

Answer 1

使用angular的位置服务，它内置于angular中，并从“ @ angular / common”导入，如下所示：

import { Component, OnInit, Input } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
import { Location } from '@angular/common';

import { Hero }         from '../hero';
import { HeroService }  from '../hero.service';

@Component({
  selector: 'app-hero-detail',
  templateUrl: './hero-detail.component.html',
  styleUrls: [ './hero-detail.component.css' ]
})
export class HeroDetailComponent implements OnInit {
  @Input() hero: Hero;

  constructor(
    private location: Location
  ) {}

  goBack() {
    this.location.back();
  }   
}

然后使用location.back（）转到上一页。这是一个工作示例：

https://stackblitz.com/angular/qvvrbgrmmda

Answer 2

这是一种获取之前路线的方法@angular/router

在原始帖子中查找更多信息

import { Injectable } from '@angular/core';
import { Router, RouterEvent, NavigationEnd } from '@angular/router';
import { filter } from 'rxjs/operators';

@Injectable({
    providedIn: "root"
})
export class PreviousRouteService {

    private previousUrl: string;
    private currentUrl: string;

    constructor(private router: Router) {

        this.currentUrl = this.router.url;
        this.previousUrl = null;

        this.router.events
                    .pipe(filter((event: RouterEvent) => event instanceof NavigationEnd))
                    .subscribe((event: NavigationEnd) => {
                        this.previousUrl = this.currentUrl;
                        this.currentUrl = event.urlAfterRedirects;
                        console.log("prev: ", this.previousUrl)
                        console.log("curr: ", this.currentUrl)
                    });

    }

    public getPreviousUrl() {
        return this.previousUrl;
    }

};

Answer 3

如果你只想要以前的路线，你可以像这样创建一个 observable

 get previousRoute$(): Observable<string> {
    return this.router.events.pipe(
      filter(e => e instanceof RoutesRecognized),
      pairwise(),
      map((e: [RoutesRecognized, RoutesRecognized]) => e[0].url)
    );
  }

现在你可以订阅这个 observable 并执行任何操作（确保你在 OnDestroy 事件上取消订阅这个 observable。）

this.previousRoute$.subscribe(url => {
  //perform your action
});

注意：当用户处于第二次导航时，此 observable 将开始发出事件。