如何在Angular 4中将md-table与服务一起使用 [英] How to use md-table with services in Angular 4

问题描述

我在Angular世界中还很陌生，我正尝试在Angular Material 2和Angular 4中使用新的md-table组件.

I am quite new in the angular world and i'm trying to use the new md-table component in Angular Material 2 with Angular 4.

我已经通过API提供了服务，该API可以检索简单的内容数组. 现在，我正在尝试将此服务用作md-table的数据源，但是我找不到从该服务获取数据的方法(它总是向我返回一个空数组).

I've made a service from an API which retrieves simple arrays of content. Now I'm trying to use this service as a data source for the md-table but I can't find a way to get the data from the service (it always return me an empty array).

请注意，在使用md-table之前，我已经在使用该服务，并且可以正常工作.

Please note that before using md-table, I was using already using the service and it worked normally.

这是组件的代码:

import { Component, OnInit, ViewChild } from '@angular/core';
import {DataSource} from '@angular/cdk';
import {MdPaginator} from '@angular/material';
import {BehaviorSubject} from 'rxjs/BehaviorSubject';
import {Observable} from 'rxjs/Observable';
import 'rxjs/add/operator/startWith';
import 'rxjs/add/observable/merge';
import 'rxjs/add/operator/map';

import { GroupService } from '../shared/group.service';
import { Group } from '../shared/group';

@Component({
  selector: 'app-group-list',
  templateUrl: './group-list.component.html',
  styleUrls: ['./group-list.component.css'],
  providers: [GroupService]
})
export class GroupListComponent implements OnInit{

  public DisplayedColumns = ['name', 'email', 'directMembersCount'];
  public groupDatabase = new GroupDatabase();
  public dataSource : CustomDataSource | any;

  @ViewChild(MdPaginator) paginator : MdPaginator;

  constructor() {}

  ngOnInit() {
    this.dataSource = new CustomDataSource(this.groupDatabase, this.paginator);
    console.log(this.dataSource);
  }

}

export class GroupDatabase implements OnInit {

  public dataChange: BehaviorSubject<Group[]> = new BehaviorSubject<Group[]>([]);
  get data(): Group[] { return this.dataChange.value }

  private _groupService : GroupService

  private getAllGroups(){
    return this._groupService
      .getAllGroups();
  }

  constructor (){}

  ngOnInit() {
      this.getAllGroups();
      console.log(this.getAllGroups());
  }
}

export class CustomDataSource extends DataSource<any> {

  constructor(private _groupDatabase = new GroupDatabase(), private _paginator: MdPaginator){
    super();
  }

  connect(): Observable<Group[]> {
    const displayDataChanges = [
      this._groupDatabase.dataChange,
      this._paginator.page
    ];
    return Observable.merge(...displayDataChanges).map(() => {
      const data = this._groupDatabase.data.slice();
      console.log(data);

      const startIndex = this._paginator.pageIndex * this._paginator.pageSize;
      return data.splice(startIndex, this._paginator.pageSize);
    })
  }

  disconnect() {}
}

这是HTML的代码:

<md-table #table [dataSource]="dataSource">

  <ng-container *cdkColumnDef="name">
    <md-header-cell *cdkCellDef>Nom</md-header-cell>
    <md-cell *cdkCellDef="let row"> {{row.name}} </md-cell>
  </ng-container>

  <ng-container *cdkColumnDef="email">
    <md-header-cell *cdkCellDef>Email</md-header-cell>
    <md-cell *cdkCellDef="let row"> {{row.email}} </md-cell>
  </ng-container>

  <ng-container *cdkColumnDef="directMembersCount">
    <md-header-cell *cdkCellDef>Nombre de membres</md-header-cell>
    <md-cell *cdkCellDef="let row"> {{row.directMembersCount}} </md-cell>
  </ng-container>

  <md-header-row *cdkHeaderRowDef="displayedColumns"></md-header-row>
  <md-row *cdkRowDef="let row; columns: DisplayedColumns;"></md-row>

</md-table>

<md-paginator #paginator
              [length]="groupDatabase.data.length"
              [pageIndex]="0"
              [pageSize]="25"
              [pageSizeOptions]="[5, 10, 25, 100]">
</md-paginator>

以及相关服务:

private groupApiUrl: string;
  private groupsApiUrl: string;
  private headers: Headers;
  constructor(public http:Http, private config: Config) {
    this.groupApiUrl = config.serverWithApi + "group";
    this.groupsApiUrl = config.serverWithApi + "groups";

    this.headers = new Headers();
    this.headers.append('Content-Type', 'application/json');
    this.headers.append('Accept', 'application/json');
  }

  public getAllGroups = (): Observable<Group[]> => {
    return this.http.get(this.groupsApiUrl)
      .map((response: Response) => <Group[]>response.json())
      .catch(this.handleError)
  }

我不确定如何使用数据源调用服务，这就是为什么我像以前那样做它；使用ngOnInit方法.

I'm not sure how I should call the service using the datasource, that's why I did it as I was doing before; using the ngOnInit method.

感谢您的帮助.

推荐答案

以下是通过HTTP检索数据的示例:

Here's an example of retrieving data through HTTP: https://plnkr.co/edit/mjQbufh7cUynD6qhF5Ap?p=preview

您丢失了一个片段，其中GroupDatabase不会在dataChange流上放置任何数据值.它是一个BehaviorSubject，它以一个空数组开头，但是您不再在其上放置任何数据.这就是为什么表只接收一个空数组的原因.

You are missing a piece where GroupDatabase does not put any data values on the dataChange stream. It is a BehaviorSubject that starts with an empty array but you do not put any more data on it. This is why the table is only receiving an empty array.

首先，要知道ngOnInit不会被Angular调用，因为GroupDatabase不是指令，也不属于更改检测周期的一部分.

First, know that ngOnInit will not be called by Angular since GroupDatabase is not a directive and is not part of the change detection cycle.

相反，将this.getAllGroups()移到GroupDatabase的构造函数.然后订阅其结果:

Instead, move this.getAllGroups() to the constructor of GroupDatabase. and then subscribe to its result:

export class GroupDatabase {
  public dataChange: BehaviorSubject<Group[]> = new BehaviorSubject<Group[]>([]);
  get data(): Group[] { return this.dataChange.value }

  constructor(groupService: GroupService) {
    groupService.getAllGroups().subscribe(data => this.dataChange.next(data));
  }
}

或者，完全摆脱GroupDatabase，让您的CustomDataSource直接调用GroupService.

Alternatively, get rid of GroupDatabase altogether and have your CustomDataSource directly call your GroupService.

export class CustomDataSource extends DataSource<Group> {

  constructor(
      private _groupService: GroupService, 
      private _paginator: MdPaginator) { }

  connect(): Observable<Group[]> {
    const displayDataChanges = [
      this._groupService.getAllGroups(),
      this._paginator.page
    ];

    return Observable.merge(...displayDataChanges).map((data, page) => {
      const clonedData = data.slice();

      const startIndex = this._paginator.pageIndex * this._paginator.pageSize;
      return data.splice(startIndex, this._paginator.pageSize);
    })
  }

  disconnect() {}
}

这篇关于如何在Angular 4中将md-table与服务一起使用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！