排序在md-table angular material2中不起作用

<md-header-cell *matHeaderCellDef md-sort-header="sortById">ID</md-header-cell>

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

import { MatSort } from '@angular/material';

@Component({
  ...
})
export class YourComponent implements OnInit {
  @ViewChild(MatSort) sort: MatSort;

  ngOnInit() {
    this.dataSource.sort = this.sort;
  }
}

import { MatSort } from '@angular/material';

@Component({
  ...
})
export class YourDataSource extends DataSource<any> {
  constructor(private sort: MatSort) {
    super();
  }

  connect(): Observable<any[]> {
    const dataMutations = [
      // 数据变更操作
    ];

    return merge(...dataMutations).pipe(map(() => {
      return this.getSortedData([...this.data]);
    }));
  }

  private getSortedData(data: any[]): any[] {
    if (!this.sort.active || this.sort.direction === '') {
      return data;
    }

    return data.sort((a, b) => {
      const isAsc = this.sort.direction === 'asc';
      // 根据排序标识符进行排序
      switch (this.sort.active) {
        case 'sortById':
          return compare(a.id, b.id, isAsc);
        // 其他排序标识符的处理
        default:
          return 0;
      }
    });
  }
}

function compare(a: number | string, b: number | string, isAsc: boolean) {
  return (a < b ? -1 : 1) * (isAsc ? 1 : -1);
}