angular - 如何在焦点上显示自动完成选项

Question

我正在用最新的 angular-material 编写一个 angular6 应用程序。
我使用组件 mat-autocomplete与 mat-input用于自动完成功能。
我想要实现的是，当用户专注于输入元素时，即使不输入任何内容，他也会看到所有可用的自动完成选项。
这是 mat-autocomplete 组件的 html 文件

<form [formGroup]="carTypeFormGroup" (ngSubmit)="okButton()">
  <mat-form-field>
    <input matInput formControlName="carCompany"
           placeholder="foo" aria-label="foo" [matAutocomplete]="autoCarCompany">
    <mat-autocomplete  #autoCarCompany="matAutocomplete">
      <mat-option *ngFor="let carCompany of filteredCarCompanies | async" [value]="carCompany">
        <span>{{carCompany}}</span>
      </mat-option>
    </mat-autocomplete>
  </mat-form-field>
...

这是组件类的代码:

@Component({
  selector: 'app-car-type',
  templateUrl: './car-type.component.html',
  styleUrls: ['./car-type.component.scss']
})
export class CarTypeComponent implements OnInit {

  carTypeFormGroup: FormGroup;

  filteredCarCompanies: Observable<CarType[]>;
  filteredCarModels: Observable<CarType[]>;
  carCompanies = [];
  carCompaniesLowercase = [];
  carModels = [];
  carTypes = [];

 private _filterCarCompanies(value: string): CarType[] {
    if (this.carCompaniesLowercase.indexOf(value.toLowerCase()) >= 0) {
      this.mainGql.GetCarModels(value).subscribe((data: any) => {
        this.carModels = [];
        data.data.car_models.forEach((row) => {
          this.carModels.push(row.model_name);
        });
      });
    }
    const filterValue = value.toLowerCase();
    return this.carCompanies.filter(carCompany => carCompany.toLowerCase().indexOf(filterValue) === 0);
  }

ngOnInit() {
    this.carTypeFormGroup = this.formBuilder.group({
      carCompany: ['', Validators.required],
      carModel: ['', Validators.required],
      carType: ['', Validators.required],
      carYear: [new Date().getFullYear(), Validators.required]
    });
    this.filteredCarCompanies = this.carTypeFormGroup.get('carCompany').valueChanges
      .pipe(startWith(''), map(carCompany => carCompany ? this._filterCarCompanies(carCompany) : this.carCompanies.slice()));
}
...
}

当我查看 mat-autocomplete示例在 https://material.angular.io/components/autocomplete/examples ，当我专注于输入元素时，我确实看到了所有结果..
有什么不同？我错过了什么？

Answer 1

过滤器在页面加载时执行。但我在 graphql 上加载了数据，因此数据在第一个过滤器执行后到达。我对其进行了更改，因此只有在收到数据后才会执行过滤器。

感谢 Swox 帮助我注意到它。

ngOnInit() {
 ...
 this.carsService.GetCarCompanies().subscribe((data: any) => {
      this.carCompanies = [];
      this.carCompaniesLowercase = [];
      data.data.car_companies.forEach((row) => {
        this.carCompanies.push(row.company_name);
        this.carCompaniesLowercase.push(row.company_name.toLowerCase());
      });
      this.filteredCarCompanies = this.carTypeFormGroup.get('carCompany').valueChanges
        .pipe(startWith(''), map(carCompany => carCompany ? this._filterCarCompanies(carCompany) : this.carCompanies.slice()));
    });