Angular 8: mat-datepicker的问题。我尝试使用[startAt]禁止在今天之前选择日期

<mat-form-field>
  <input matInput [matDatepicker]="picker" placeholder="Choose a date" [startAt]="today()">
  <mat-datepicker-toggle matSuffix [for]="picker"></mat-datepicker-toggle>
  <mat-datepicker #picker></mat-datepicker>
</mat-form-field>

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

@Component({
  selector: 'app-datepicker-example',
  templateUrl: 'datepicker-example.html',
  styleUrls: ['datepicker-example.css'],
})
export class DatepickerExample {
  constructor(private dateAdapter: DateAdapter<Date>) {}

  today(): Date {
    const today = new Date();
    this.dateAdapter.setLocale('en-US'); // 设置日期适配器的语言环境
    return today;
  }
}