How to set autofocus on a matInput element on click event in Angular 6?

问题

Similar to Google Login page, I want to have autofocus on input element after on click event. I have tried @ViewChild('id') and document.getElementId('id'). Both of it doesn't work. It's always null or undefined. How can I achieve this?

       <mat-form-field class="example-full-width col-sm-4">
        <input autofocus id="login-username" matInput 
       formControlName="userName" minlength="5" maxlength="20" 
       name="userName" placeholder="Username" required #input> 
      </mat-form-field>

        <div class="col-sm-12">
           <button (click)="changeView()" type="button" mat-raised-
             button color="primary">Next</button>
          </div>

         <mat-form-field class="example-full-width col-sm-4" 
          #passwordInput>
        <input autofocus type="password" matInput 
       placeholder="Password" minlength="5" maxlength="20" 
       formControlName="userPassword" #passwordInput>  
      </mat-form-field>

回答1:

Unfortunately all other solutions do not work with autofocusing matInput at the moment of rendering.

The reason is that one should use a high-level api of the matInput instead of attempting to focus the input itself.

What should be done instead is calling matInput.focus(). Here is a simple directive that uses this approach:

import { Directive, OnInit } from '@angular/core';
import { MatInput } from '@angular/material';

@Directive({
  selector: '[matInputAutofocus]',
})
export class AutofocusDirective implements OnInit {

  constructor(private matInput: MatInput) { }

  ngOnInit() {
    setTimeout(() => this.matInput.focus());
  }

}

The timeout is required to delay focusing the element because matInput does not properly function at the moment of creating yet. Usage:

<mat-form-field>
  <input type="text" matInput matInputAutofocus>
</mat-form-field>

Of course, naming the selector matInputAutofocus is dangerous because material itself can come to this solution one day. Use it on your own risk or just rename with your prefix (recommended).

回答2:

If you want to set focus to an Input field as soon as the page loads, you can do it simply by applying HTML attribute to that element, such as :

<input type="text" #input1 autofocus>

Else if you want to do this from your component.ts conditionally, use:

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

 @ViewChild('input1') inputEl:ElementRef;

 ngAfterViewInit() {
 this.inputEl.nativeElement.focus();
 }

Or you can use:

First import the renderer2 from @angular/core and then,

    const element = this.renderer.selectRootElement('#input1');

 setTimeout(() => element.focus(), 0);

Whatever you seems to be comfortable with your existing code.

回答3:

When you use Angular Material, you can use cdkFocusInitial to tell the library where you want to focus after component is ready. No native approaches are required:

<mat-form-field class="example-full-width">
  <mat-label>My Label</mat-label>
  <textarea 
    cdkFocusInitial           <---------
    cdkTextareaAutosize
    matInput>
  </textarea>
</mat-form-field>

回答4:

You need to use template ref to input element then use ViewChild it will work

Example: https://stackblitz.com/edit/angular-frqm8b

 <mat-form-field class="example-full-width col-sm-4">
        <input autofocus id="login-username" matInput 
       formControlName="userName" minlength="5" maxlength="20" 
       name="userName" placeholder="Username" required #input> 
      </mat-form-field>

        <div class="col-sm-12">
           <button (click)="changeView()" type="button" mat-raised-
             button color="primary">Next</button>
          </div>

         <mat-form-field class="example-full-width col-sm-4" 
          >
        <input autofocus type="password" matInput 
        ****#passwordInput****
       placeholder="Password" minlength="5" maxlength="20" 
       formControlName="userPassword" #passwordInput>  
      </mat-form-field>

来源：https://stackoverflow.com/questions/51510936/how-to-set-autofocus-on-a-matinput-element-on-click-event-in-angular-6