Angular mat-table可扩展行:如何自动扩展第一行？当我折叠它的时候该如何控制？

<mat-table [dataSource]="dataSource">
  <!-- 表格列定义 -->
  <ng-container matColumnDef="column1">
    <mat-header-cell *matHeaderCellDef> Column 1 </mat-header-cell>
    <mat-cell *matCellDef="let element"> {{element.column1}} </mat-cell>
  </ng-container>

  <!-- 其他列定义 -->

  <!-- 展开行定义 -->
  <ng-container matColumnDef="expandedRow">
    <mat-cell *matCellDef="let element" [attr.colspan]="displayedColumns.length">
      <ng-container *ngIf="expandedRow === element">
        <!-- 展开行的内容 -->
        <div>Expanded content for {{element.column1}}</div>
      </ng-container>
    </mat-cell>
  </ng-container>

  <!-- 表格行定义 -->
  <mat-row *matRowDef="let row; columns: displayedColumns;"></mat-row>
  <mat-row *matRowDef="let row; columns: ['expandedRow']; when: isExpanded"></mat-row>
</mat-table>

import { Component } from '@angular/core';

@Component({
  selector: 'app-table',
  templateUrl: './table.component.html',
  styleUrls: ['./table.component.css']
})
export class TableComponent {
  dataSource: any[] = [
    { column1: 'Data 1' },
    { column1: 'Data 2' },
    { column1: 'Data 3' }
  ];
  displayedColumns: string[] = ['column1'];
  expandedRow: any;

  isExpanded = (index: number, row: any) => this.expandedRow === row;

  toggleExpand(row: any) {
    this.expandedRow = this.expandedRow === row ? null : row;
  }
}