angular - 如何为 Subject RxJS observable 分配初始值？

Question

我正在开发一个 Angular 2 应用程序，我需要更改列表中列的顺序，单击标题(作为数据表工作)，我从 Angularfire 2 文档示例中得到一个想法，这是我的代码:(grupos.component.ts)

import { Component, OnInit } from '@angular/core';
import { AngularFire, FirebaseListObservable, FirebaseObjectObservable    }  from 'angularfire2';
import { Subject } from 'rxjs/Subject';
import {AF} from "../providers/af";
import { Router } from "@angular/router";
{ EditGpoComponent } from '../edit-gpo/edit-gpo.component';

@Component({
  selector: 'app-grupos',
  templateUrl: './grupos.component.html',
  styleUrls: ['./grupos.component.css']
})

export class GruposComponent implements OnInit {
  public newMessage: string;
  eventos: FirebaseListObservable<any[]>;
  sizeSubject: Subject <any>;

 constructor( af: AngularFire, private router: Router ) {
    this.sizeSubject = new Subject();
    this.eventos = af.database.list('/eventos', {
          query: {
           orderByChild: this.sizeSubject

          }
        });
  }

  filterBy(size: string) {
   this.sizeSubject.next(size); 

   }

  editaGrupo(keyGrupo){

    this.router.navigate(['/add-gpo']);
  }

  ngOnInit() {

  }

}

这是我的 Grupos.components.html 的代码:

<div class="container">


<br><br><br>
  <div class="row"> 
  <a href="#" class="btn btn-info" routerLink="/add-gpo">+Add New Event</a> 
  <br><br>
   <table class="table table-striped">
   <thead>
   <tr>
    <th><button (click)="filterBy('evento')">EVENT</button></th>
    <th><button (click)="filterBy('arrival')">ARRIVAL</button></th>
    <th><button (click)="filterBy('departure')">DEPARTURE</button></th>
    <th><button (click)="filterBy('hotel')">VENUE</button></th>
    <th><button (click)="filterBy('pax')">PAX</button></th>
    <th>FUNCTIONS</th>
    </tr> 
   </thead>
   <tbody>
   <tr *ngFor="let evento of eventos | async ">
        <td>{{evento.evento}}</td>
        <td>{{evento.arrival}}</td>
        <td>{{evento.departure}}</td>
      <td>{{evento.hotel}}</td>
      <td>{{evento.pax}}</td>
      <td style="font-size: 1.2em">
      <a href="#" [routerLink]="['/editGpo']" [queryParams]="{eveId: evento.$key}"><span class="glyphicon glyphicon-edit" aria-hidden="true" title="edit event"></span></a>
      <a href="#"><span class="glyphicon glyphicon-user" aria-hidden="true" title="attendees"></span></a>
      <a href="#"><span class="glyphicon glyphicon-bullhorn" aria-hidden="true" title="speakers"></span></a>
      <a href="#"><span class="glyphicon glyphicon-trash glyphicon " aria-hidden="true" title="delete event"></span></a>

      </td>
    </tr>
    </tbody>

</table>
</div>
</div>

如您所见，它的工作非常出色，每次我单击列标题按钮时，我的表格都会获得该列的顺序。但我一直在寻找如何为“sizeSubject”(主题)赋予初始值的时间，我喜欢在“evento”上分配值，因此表格显示时按 evento 排序。现在只需向我显示按钮标题和空白表格，如果我单击任何按钮，它会按该顺序向我显示表格。

任何提示或意见将不胜感激!

Answer 1

如果您想要一个具有“初始值”的 Subject，更好的 RxJS 类是 BehaviorSubject。

使用 BehaviorSubject，您将初始值传递给它的构造函数。