Angular5 - TypeError: Cannot read property 'template' of undefined

Question

I have added EDIT, DELETE and DETAILS buttons to each row in mat-table using Angular [email protected]. All buttons are working but, * I am getting an error "Cannot read property 'template' of undefined" and * for each button click, everything is displaying on the same page

itemlist.component.html

<mat-table #table [dataSource]="dataSource">
  <ng-container matColumnDef="name">
    <mat-header-cell *matHeaderCellDef> Name </mat-header-cell>
    <mat-cell *matCellDef="let row"> {{row.name}} </mat-cell>
  </ng-container>

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

  <ng-container matColumnDef="actions">
    <mat-cell *matCellDef="let row">
      <button mat-button (click)="showDetails(row)">DETAILS</button>
      <button mat-button (click)="editItem(row)">EDIT</button>
      <button mat-button (click)="deleteItem(row)">DELETE</button>
    </mat-cell>
  </ng-container>

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

itemlist.component.ts

export class ItemListComponent {
  @Input() dataSource;
  displayedColumns = ['name', 'description', 'actions'];

  @Input() items: Item[];
  @Output() onEdit = new EventEmitter<Item>();
  @Output() onShow = new EventEmitter<Item>();
  @Output() onDelete = new EventEmitter<Item>();

  itemsTrackByFn = (index: string, item: Item) => item.id;

  showDetails(item: Item) {
    this.onShow.emit(item);
  }
  editItem(item: Item) {
    this.onEdit.emit(item)
  }
  deleteItem(item: Item) {
    this.onDelete.emit(item)
  }
}

itemindex.component.html

<app-item-list [dataSource]="dataSource"
              (onShow)="showItem($event)"
              (onDelete)="deleteItem($event)"
              (onEdit)="editItem($event)"
></app-item-list>

itemindex.component.ts

export class ItemIndexComponent implements OnInit {
  items$: Observable<Item[]>;
  public dataSource: ItemsDatasource;

  constructor(public store: Store<fromRoot.State>, private router: Router){}

  ngOnInit() {
    this.items$ = this.store.select(fromItems.getAllItems);
    this.store.dispatch(new itemsActions.LoadAll());
    this.dataSource = new ItemsDatasource(this.items$);
  }

  editItem(item: Item) {
    this.store.dispatch(new itemsActions.SetCurrentItemId(item.id));
    this.router.navigate(['/items', item.id, 'edit'])
  }
  showItem(item: Item) {
    this.store.dispatch(new itemsActions.SetCurrentItemId(item.id));
    this.router.navigate(['/items', item.id])
  }
  deleteItem(item: Item) {
     this.store.dispatch(new itemsActions.Delete(item.id));
   }
 }
}


export class ItemsDatasource extends DataSource<Item> {

  public constructor(private items$: Observable<Item[]>) {
    super()
  }

  public connect(collectionViewer: CollectionViewer): Observable<Item[]> {
    return this.items$;
  }

  public disconnect(collectionViewer: CollectionViewer): void {}
}

Any suggestion would be helpful

Answer 1

I forgot to define the header cell for the actions. So it was throwing that error. Here is the code which solved this problem.

<ng-container matColumnDef="actions">
  <mat-header-cell *matHeaderCellDef></mat-header-cell>
  <mat-cell *matCellDef="let row">
    <button mat-button (click)="showDetails(row)">DETAILS</button>
    <button mat-button (click)="editItem(row)">EDIT</button>
    <button mat-button (click)="deleteItem(row)">DELETE</button>
  </mat-cell>
</ng-container>