Angular matSort not working

Question

I'm having trouble with importing matSort into my matTable.

I'm providing you with my code:

dashboard.component.ts

import {Component, ViewChild} from '@angular/core';
import {UserService} from "../user.service";
import {DohvatMantisaService} from "../dohvat-mantisa.service";
import {Mantisi} from "../Mantisi";
import {Observable} from "rxjs/Observable";
import {DataSource} from "@angular/cdk/collections";
import 'rxjs/add/observable/of';
import 'rxjs/add/operator/startWith';
import 'rxjs/add/observable/merge';
import {MatSort} from '@angular/material';
@Component({
  selector: 'app-dashboard',
  templateUrl: './dashboard.component.html',
  styleUrls: ['./dashboard.component.css']
})
export class DashboardComponent{
  displayedColumns = ['projekt', 'manits', 'kategorija','ozbiljnost','datum_prijave','postavio','odjel','postavio','naziv','status','planirana_isporuka'];
  constructor(private user:UserService, private dohvatMantisa:DohvatMantisaService) {
  }
  dataSource: TableDataSource | null;
  mantisi: Mantisi[];
  name = this.user.getUsername();
  @ViewChild(MatSort) sort: MatSort;
  ngOnInit() {
    this.dataSource = new TableDataSource(this.dohvatMantisa,this.sort);
  }
}

export class TableDataSource extends DataSource<Mantisi>{
  constructor(private mantisiDS: DohvatMantisaService,private sort: MatSort){
    super();
  }
  connect(): Observable<Mantisi[]> {
    const displayDataChanges = [
      this.mantisiDS.dohvatiMantise(),
      this.sort.sortChange,
    ];

    return Observable.merge(...displayDataChanges).map(() => {
      return this.getSortedData();
    });
  }
  disconnect() {}

  getSortedData(): Mantisi[]{
    const data = this.mantisiDS.prikazMantisa().slice();
    if (!this.sort.active || this.sort.direction == '') { return data; }
    return data.sort((a, b) => {
      let propertyA: number|string = '';
      let propertyB: number|string = '';
      switch (this.sort.active) {
        case 'projekt': [propertyA, propertyB] = [a.projekt, b.projekt]; break;
        case 'manits': [propertyA, propertyB] = [a.manits, b.manits]; break;
        case 'kategorija': [propertyA, propertyB] = [a.kategorija, b.kategorija]; break;
        case 'ozbiljnost': [propertyA, propertyB] = [a.ozbiljnost, b.ozbiljnost]; break;
        case 'datum_prijave': [propertyA, propertyB] = [a.datum_prijave, b.datum_prijave]; break;
        case 'postavio': [propertyA, propertyB] = [a.postavio, b.postavio]; break;
        case 'naziv': [propertyA, propertyB] = [a.naziv, b.naziv]; break;
        case 'status': [propertyA, propertyB] = [a.status, b.status]; break;
        case 'planirana_isporuka': [propertyA, propertyB] = [a.planirana_isporuka, b.planirana_isporuka]; break;
      }

      let valueA = isNaN(+propertyA) ? propertyA : +propertyA;
      let valueB = isNaN(+propertyB) ? propertyB : +propertyB;

      return (valueA < valueB ? -1 : 1) * (this.sort.direction == 'asc' ? 1 : -1);
    });
  }
}

This is my service: dohvatMantisaService

import { Injectable } from '@angular/core';
import {Http, Response, RequestOptions, Headers} from "@angular/http";
import {Observable} from "rxjs/Observable";
import {Mantisi} from "./Mantisi";
import 'rxjs';
import 'rxjs/operator/map';
import 'rxjs/operator/do';

@Injectable()
export class DohvatMantisaService {
  constructor(public http:Http) { }
  result: Mantisi[];
  dohvatiMantise(): Observable<Mantisi[]>{
    return this.http.get('/mantis/getMantisReport').map(this.extractData);
  }
  private extractData(response: Response) {
    let body = response.json();
    return body || {};
  }

  prikazMantisa(): Mantisi[]{
    this.dohvatiMantise().subscribe(res => this.result = res);
    return this.result;
  }
}

And im providing you with my dashboard.component.html matSort row:

<mat-table #table [dataSource]="dataSource" class="example-table" matSort>

The main problem here is that data is loaded and acquired from http request but I'm getting errors in console something like this:

Cannot read property 'sortChange' of undefined at TableDataSource.webpackJsonp.../../../../../src/app/dashboard/dashboard.component.ts.TableDataSource.connect (dashboard.component.ts:36) at MatTable.webpackJsonp.../../../cdk/esm5/table.es5.js.CdkTable._observeRenderChanges (table.es5.js:602) at MatTable.webpackJsonp.../../../cdk/esm5/table.es5.js.CdkTable.ngAfterContentChecked (table.es5.js:522)

It tells me that this.sort.sortChange is undefined. I searched all bit of internet and couldn't find proper answer. Hope you can help me with that.

Answer 1

I had a similar issue when passing async data from a container layer to the component layer. Here's my solution

Because the element started off with no data, there's no use to put a constructor or an OnInit as the original example does. Only After the data stream comes in (async) I implement the sort and paginator in a setter, and everything worked perfectly.

In my template:

<div class="card">

    <div class="card-header">
      <h4>{{pageTitle}}</h4>
      <mat-form-field>
        <input matInput (keyup)="applyFilter($event.target.value)" placeholder="Filter">
      </mat-form-field>
    </div>

    <div class="card-body p-0">    
      <div class="mat-elevation-z8">
        <table mat-table [dataSource]="dataSource" matSort>

          <ng-container matColumnDef="projectNumber">
            <th mat-header-cell *matHeaderCellDef mat-sort-header> Werf Nummer </th>
            <td mat-cell *matCellDef="let row"> W{{row.projectNumber}} </td>
          </ng-container>

          <ng-container matColumnDef="description">
            <th mat-header-cell *matHeaderCellDef mat-sort-header> Omschrijving </th>
            <td mat-cell *matCellDef="let row"> {{row.description}} </td>
          </ng-container>

          <tr mat-header-row *matHeaderRowDef="displayedColumns"></tr>
          <tr mat-row *matRowDef="let row; columns: displayedColumns;">
          </tr>
        </table>

        <mat-paginator [pageSizeOptions]="[10,20,100]"></mat-paginator>
      </div>      
    </div>
  </div>

In my angular component class i have

    export class ProjectListComponent {
      pageTitle = 'Projects';
      displayedColumns: string[] = ['projectNumber', 'description'];
      dataSource: MatTableDataSource<Project>;

      @ViewChild(MatPaginator, {static: true}) paginator: MatPaginator;
      @ViewChild(MatSort, {static: true}) sort: MatSort;
      @Input() set projects(value: Project[]){
        this.dataSource = new MatTableDataSource(value);
        this.dataSource.paginator = this.paginator;
        this.dataSource.sort = this.sort;
      }
      @Input() selectedProject: Project;
      @Output() selected = new EventEmitter<Project>();

      applyFilter(filterValue: string) {
        this.dataSource.filter = filterValue.trim().toLowerCase();

        if (this.dataSource.paginator) {
          this.dataSource.paginator.firstPage();
        }
      }
    }

I should mention something else that's really interesting about the filtering option. Note that project here only gets used for two fields but the interface is actually more fields than that, for instance it has an ID. Even though I'm not showing the ID, I can filter by ID with the above code which is pretty awesome.

    export interface Project {
        id: string;
        projectNumber: string;
        description: string;
        activePeriods: ProjectActivePeriod[];
    }

Also note that it's obligated that the matColumnDef="projectNumber" reference in you displayedColumns has to be the exact name of a property in the interface. If I had used 'ProjectNumber', the sort would not work.

I build this based on the info of

• example in stackblitz - Data table with sorting, pagination, and filtering.
• documentation on pagination

Answer 2

So it's happening because of your this.sort.sortChange method is getting called before your child view Initialize

You Just need to implement your class from AfterViewInit instead of OnInit

And use ngAfterViewInit life cycle method

export class ApplicantListComponent implements AfterViewInit {
    @ViewChild(MatPaginator, { static: false }) paginator: MatPaginator;
    @ViewChild(MatSort, { static: false }) sort: MatSort;

    constructor() {}

    ngAfterViewInit() {
        this.sort.sortChange.subscribe(() => {
            this.paginator.pageIndex = 0;
            this.paginator.pageSize = this.pageSize;
        });
}