角度5材料自动完成，位置错误

我正在尝试在角度材料网站上提供自动完成的example，当我在应用程序中实现它时，选项出现在其他地方而不是在输入下如图所示

我目前在 html file 中有以下代码

<form class="example-form">
    <mat-form-field class="example-full-width">
      <input matInput placeholder="State" aria-label="State" 
       [matAutocomplete]="auto" [formControl]="stateCtrl">
      <mat-autocomplete #auto="matAutocomplete">
        <mat-option *ngFor="let state of filteredStates | async" 
          [value]="state.name">
          <img class="example-option-img" aria-hidden [src]="state.flag" 
            height="25">
          <span>{{state.name}}</span> |
          <small>Population: {{state.population}}</small>
        </mat-option>
      </mat-autocomplete>
    </mat-form-field>
</form>

这就是我所拥有的 component.ts file

import { FormControl } from '@angular/forms';
import { Observable } from 'rxjs';
import { map, startWith } from 'rxjs/operators';

  stateCtrl = new FormControl();
  filteredStates: Observable < State[] >;

  states: State[] = [
    {
      name: 'Arkansas',
      population: '2.978M',
      // https://commons.wikimedia.org/wiki/File:Flag_of_Arkansas.svg
      flag: 'https://upload.wikimedia.org/wikipedia/commons/9/9d/Flag_of_Arkansas.svg'
    }, {
      name: 'California',
      population: '39.14M',
      // https://commons.wikimedia.org/wiki/File:Flag_of_California.svg
      flag: 'https://upload.wikimedia.org/wikipedia/commons/0/01/Flag_of_California.svg'
    }, {
      name: 'Florida',
      population: '20.27M',
      // https://commons.wikimedia.org/wiki/File:Flag_of_Florida.svg
      flag: 'https://upload.wikimedia.org/wikipedia/commons/f/f7/Flag_of_Florida.svg'
    }, {
      name: 'Texas',
      population: '27.47M',
      // https://commons.wikimedia.org/wiki/File:Flag_of_Texas.svg
      flag: 'https://upload.wikimedia.org/wikipedia/commons/f/f7/Flag_of_Texas.svg'
    }
  ];

  constructor() {
    this.filteredStates = this.stateCtrl.valueChanges.pipe(startWith(''),
      map(state => state ? this._filterStates(state) : this.states.slice()));
  }

  private _filterStates(value: string): State[] {
    const filterValue = value.toLowerCase();
    return this.states.filter(state => state.name.toLowerCase().indexOf(filterValue) === 0);
}

在我的 app.module.ts 中，我有进口内的formsmodule和reactiveformsmodule .

任何想法为什么选项没有出现在输入下，如何解决问题将不胜感激 .

忘记添加，父组件调用此子组件（自动完成），如下所示 .

<div>
...
  <app-menu></app-menu>
...
</div>