使用FormControlName作为选择器进行聚焦

<form>
  <input type="text" formControlName="username">
</form>

import { Component } from '@angular/core';
import { FormBuilder, FormGroup } from '@angular/forms';

@Component({
  selector: 'app-example',
  templateUrl: './example.component.html',
  styleUrls: ['./example.component.css']
})
export class ExampleComponent {
  form: FormGroup;

  constructor(private formBuilder: FormBuilder) {
    this.form = this.formBuilder.group({
      username: ''
    });
  }
}

import { Component, ViewChild, ElementRef } from '@angular/core';

@Component({
  selector: 'app-example',
  templateUrl: './example.component.html',
  styleUrls: ['./example.component.css']
})
export class ExampleComponent {
  @ViewChild('usernameInput') usernameInput: ElementRef;

  focusUsername() {
    this.usernameInput.nativeElement.focus();
  }
}

<form>
  <input type="text" formControlName="username" #usernameInput>
  <button (click)="focusUsername()">Focus Username</button>
</form>