Dynamic matHeaderRowDef in mat-table Angular

Question

I'm about to bind the group header row in the mat-table dynamically. But the DOM couldn't find the headerId.

HTML:

<ng-container *ngFor="let result of headerData; let i = index">

                <ng-container [matColumnDef]="header-row-'+i+'-group">

                    <th mat-header-cell *matHeaderRowDef

                        [style.text-align]="center"

                        [attr.colspan]=result.Count>

                        {{result.Name}}

                    </th>

                </ng-container>

</ng-container>

<tr mat-header-row *matHeaderRowDef="groupHeaderColumns"></tr>

<tr mat-header-row *matHeaderRowDef="columnNames"></tr>

Typescript:

this.groupHeaderColumns = ['header-row-1-group', 'header-row-2-group']

Tried,

1. headerRow as 'header-row-1-group' static but still the same error
2. Replaced Div instead of ng-container

Error: Couldnot find the header with id header-row-1-group

Where am i wrong and what change i should do?

Answer 1

Try the below change, you need to join strings

index starts at zero, so we can do i+1 to get the correct value! Instead I directly used groupHeaderColumns names!

Also you need to use matHeaderCellDef instead of matHeaderRowDef!

  <ng-container
    *ngFor="let result of headerData; let i = index"
    matColumnDef="{{groupHeaderColumns[i]}}"
  >
    <th
      mat-header-cell
      *matHeaderCellDef
      [style.text-align]="'center'"
      [attr.colspan]="result.Count"
    >
      {{result.Name}}
    </th>
  </ng-container>

FULL CODE:

TS:

import { CommonModule } from '@angular/common';
import { Component } from '@angular/core';
import { MatTableModule } from '@angular/material/table';

export interface PeriodicElement {
  name: string;
  position: number;
  weight: number;
  symbol: string;
}

const ELEMENT_DATA: PeriodicElement[] = [
  { position: 1, name: 'Hydrogen', weight: 1.0079, symbol: 'H' },
  { position: 2, name: 'Helium', weight: 4.0026, symbol: 'He' },
  { position: 3, name: 'Lithium', weight: 6.941, symbol: 'Li' },
  { position: 4, name: 'Beryllium', weight: 9.0122, symbol: 'Be' },
  { position: 5, name: 'Boron', weight: 10.811, symbol: 'B' },
  { position: 6, name: 'Carbon', weight: 12.0107, symbol: 'C' },
  { position: 7, name: 'Nitrogen', weight: 14.0067, symbol: 'N' },
  { position: 8, name: 'Oxygen', weight: 15.9994, symbol: 'O' },
  { position: 9, name: 'Fluorine', weight: 18.9984, symbol: 'F' },
  { position: 10, name: 'Neon', weight: 20.1797, symbol: 'Ne' },
];

/**
 * @title Basic use of `<table mat-table>`
 */
@Component({
  selector: 'table-basic-example',
  styleUrl: 'table-basic-example.css',
  templateUrl: 'table-basic-example.html',
  standalone: true,
  imports: [MatTableModule, CommonModule],
})
export class TableBasicExample {
  displayedColumns: string[] = ['position', 'name', 'weight', 'symbol'];
  dataSource = ELEMENT_DATA;
  show = false;
  headerData: any = [
    {
      Count: 2,
      Name: 'one',
    },
    {
      Count: 2,
      Name: 'two',
    },
  ];
  groupHeaderColumns: any = ['header-row-1-group', 'header-row-2-group'];
}

HTML

<table mat-table [dataSource]="dataSource" class="mat-elevation-z8">
  <!--- Note that these columns can be defined in any order.
        The actual rendered columns are set as a property on the row definition" -->

  <!-- Position Column -->
  <ng-container matColumnDef="position">
    <th mat-header-cell *matHeaderCellDef>No.</th>
    <td mat-cell *matCellDef="let element">{{element.position}}</td>
  </ng-container>

  <!-- Name Column -->
  <ng-container matColumnDef="name">
    <th mat-header-cell *matHeaderCellDef>Name</th>
    <td mat-cell *matCellDef="let element">{{element.name}}</td>
  </ng-container>

  <!-- Weight Column -->
  <ng-container matColumnDef="weight">
    <th mat-header-cell *matHeaderCellDef>Weight</th>
    <td mat-cell *matCellDef="let element">{{element.weight}}</td>
  </ng-container>

  <!-- Symbol Column -->
  <ng-container matColumnDef="symbol">
    <th mat-header-cell *matHeaderCellDef>Symbol</th>
    <td mat-cell *matCellDef="let element">{{element.symbol}}</td>
  </ng-container>

  <ng-container
    *ngFor="let result of headerData; let i = index"
    matColumnDef="{{groupHeaderColumns[i]}}"
  >
    <th
      mat-header-cell
      *matHeaderCellDef
      [style.text-align]="'center'"
      [attr.colspan]="result.Count"
    >
      {{result.Name}}
    </th>
  </ng-container>

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

Stackblitz Demo