问远程dataSource不显示在带有MatTableDataSource的席表中

EN

    <div class="mat-elevation-z8">
  <mat-form-field>
    <input matInput (keyup)="applyFilter($event.target.value)" placeholder="Filter">
  </mat-form-field>

  <table mat-table [dataSource]="dataSource" matSort style="width: 100%;">

    <ng-container matColumnDef="accountType">
      <th mat-header-cell *matHeaderCellDef mat-sort-header> Account Type </th>
      <td mat-cell *matCellDef="let e"> {{e.accountType}} </td>
    </ng-container>

    <ng-container matColumnDef="id">
      <th mat-header-cell *matHeaderCellDef mat-sort-header> ID </th>
      <td mat-cell *matCellDef="let e"> {{e.id}} </td>
    </ng-container>

    <tr mat-header-row *matHeaderRowDef="columnsToDisplay"></tr>
    <tr mat-row *matRowDef="let row; columns: columnsToDisplay;"></tr>
  </table>
  <mat-paginator [pageSizeOptions]="[5, 10, 20]" showFirstLastButtons></mat-paginator>
</div>

import { Component, OnInit, ViewChild } from '@angular/core';
import { MatPaginator, MatTableDataSource, MatSort } from '@angular/material';

import { HeadAccount } from '../../Data/HeadAccount';
import { HeadAccountsService } from '../../Services/head-accounts.service';

import { AfterViewInit } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-head-accounts',
  templateUrl: './head-accounts.component.html',
  styleUrls: ['./head-accounts.component.css']
})
export class HeadAccountsComponent implements OnInit {

  constructor(private haser: HeadAccountsService) { }

  ngOnInit() {
    this.gets();
  }

  ngAfterViewInit() {
    this.dataSource.paginator = this.paginator;
    this.dataSource.sort = this.sort;
  }

  has: HeadAccount[];
  dataSource = new MatTableDataSource(this.has);
  columnsToDisplay: string[] = ['accountType', 'id'];
  @ViewChild(MatPaginator) paginator: MatPaginator;
  @ViewChild(MatSort) sort: MatSort;

  gets(): void {
    this.haser.gets()
      .subscribe(has => this.has = has);
  }
  applyFilter(filterValue: string) {
    this.dataSource.filter = filterValue.trim().toLowerCase();
  }
}