需要帮助从 Angular 2 中的服务访问变量

Question

将用户上一页的 URL id 传递给我可以在对话框中引用的服务。

issuer.service.ts

import { Injectable, EventEmitter } from '@angular/core';
import { Observable, of } from 'rxjs';
import { BehaviorSubject } from 'rxjs';

@Injectable()
export class IssuerService {


private urlidSource = new BehaviorSubject<string>('');
currentUrlid = this.urlidSource.asObservable();
public onChange: EventEmitter<string> = new EventEmitter<string>();

  constructor () {
  }

  changeUrlid(urlid: string) {
    this.currentUrlid = of(urlid);
    this.onChange.emit(urlid);
  }

  getUrlid(currentUrlid: string) {
    return this.currentUrlid;
  }


}

具有我想要的 URL id 的页面 (dashboard.component.ts)

import { IssuerService } from './../../issuer.service';
import { ActivatedRoute } from '@angular/router';
import { Router } from '@angular/router';
urlid: string;
  constructor(
    private route: ActivatedRoute,
    private router: Router,
    private issuerService: IssuerService,
    public dialog: MatDialog
  ) {}

newUrlid() {
  this.issuerService.changeUrlid(this.route.snapshot.paramMap.get('id'));
  console.log(this.urlid);
}

  ngOnInit() {
    // Get URL ID
    this.issuerService.onChange.subscribe(urlid => this.urlid = urlid);
    this.newUrlid();
}

组件我要读取的值：

    import { ActivatedRoute } from '@angular/router';
    import { Router } from '@angular/router';
    import { IssuerService } from './../../issuer.service';

        urlid: string;

        constructor(
          private route: ActivatedRoute,
          private router: Router,
          private issuerService: IssuerService,
          public dialog: MatDialog
        ) {}

  ngOnInit() {
 this.issuerService.onChange.subscribe(urlid => {
           this.urlid = urlid;
           console.log(this.urlid);
   });

  }

所以目前当我访问我的仪表板页面时，它会显示正确的值 2。我的目标是，当用户访问任何页面时，我可以读取此值 2。如何访问此值？上面的代码有效，我的 Header 显示 2 但仅在仪表板页面上时才显示。无论用户在哪个页面上，我都需要它显示 2。

Answer 1

你可以看到这个example，它是修改列表：

• 使用 queryPamas 获取查询字符串，而不是参数（DashboardComponent）

• 使用ReplaySubject(1)返回最后一个urlId；它没有默认值，只返回前一个值（IssuerService）

• 从 getUrlid 获取 observable 并在想要显示 url id 的组件中订阅它

export class IssuerService {


  private urlidSource = new ReplaySubject<string>(1);

  constructor() {
  }

  changeUrlid(urlid: string) {
    this.urlidSource.next(urlid);
  }

  getUrlid() {
    return this.urlidSource;
  }

}

export class DashboardComponent implements OnInit {

  urlid: string;
  constructor(
    // private route: ActivatedRoute,
    private router: Router,
    private issuerService: IssuerService,
    // public dialog: MatDialog
  ) { }

  newUrlid() {
    // Get URL ID
    this.route.queryParams.subscribe((queryParam) => {
      const id = queryParam['id'];
      if (!id) {
        return;
      }
      this.issuerService.changeUrlid(id);
    });
  }

  ngOnInit() {
    this.newUrlid();

    this.issuerService.getUrlid().subscribe(urlid => {
      this.urlid = urlid;
    });
  }

}

export class HelloComponent implements OnInit {
  urlid;
  constructor(
    private issuerService: IssuerService
  ) { }

  ngOnInit() {
    this.issuerService.getUrlid().subscribe(urlid => {
      this.urlid = urlid;
    });
  }
}

Answer 2

您的 get 方法不需要参数，因为您已经在服务中获得了值，

  getUrlid() {
    return this.currentUrlid;
  }

您可以使用检索第二个组件中的值，如下所示，

this.issuerService.currentUrlid.subscribe((value: string) => {
         this.urlid = value;
}