如何将焦点设置为另一个输入？

Question

I need to be able to switch focus to an input element when some event occurs. How do I do that in Angular 2?

For example:

<input (keyUp)="processKeyUp($event)"/>
<input (focusme)="alert('i am focused')"/>

I want to focus the 2nd input box when a certain key is pressed in the first. I think I need to use a custom event ( focusme in the snippet), but I don't know where or how to declare it, and whether to use a @Directive annotation for it, or include its definition in a component somehow. In short, I am stumped.

UPDATE

Forgot to mention, I know I can do that by using local variables in the html, but I want to be able to do it from the component, and I want to be able to do complex logic when firing the focusme event so that controls listening to it can determine if it is meant for them or not. Thanks!

Answer 1

You can do this just passing the second input as a variable to the first one

For example

HTML

<!-- We pass focusable as a parameter to the processKeyUp function -->
<input (keyup)="processKeyUp($event, focusable)"/>

<!-- With #focusable we are creating a variable which references to the input -->
<input #focusable /> 

Later in your js/ts

@Component({
  selector: 'plunker-app'
})
@View({
  templateUrl: 'main.html'
})
class PlunkerApp {

  constructor() {
  }

  processKeyUp(e, el) {
    if(e.keyCode == 65) { // press A
      el.focus();
    }
  }
}

el is the raw element, so you can use pure javascript on it.

Here's a plnkr so you can see it working.

I hope it helps.

Answer 2

For manipulation on DOM elements always try to use Directives. In this case you are able to write simple directive.

For accessing DOM from directive we can inject reference of our host DOM element by the ElementRef in directive constructor.

constructor(@Inject(ElementRef) private element: ElementRef) {}

For change detection of binded value we can use ngOnChanges livecycle method.

protected ngOnChanges() {}

All other stuff is simple.

Simple solution

// Simple 'focus' Directive
import {Directive, Input, ElementRef} from 'angular2/core';
@Directive({
    selector: '[focus]'
})
class FocusDirective {
    @Input()
    focus:boolean;
    constructor(@Inject(ElementRef) private element: ElementRef) {}
    protected ngOnChanges() {
        this.element.nativeElement.focus();
    }
}

// Usage
@Component({
    selector : 'app',
    template : `
        <input [focus]="inputFocused" type="text">
        <button (click)="moveFocus()">Move Focus</button>
    `,
    directives: [FocusDirective]
})
export class App {
    private inputFocused = false;
    moveFocus() {
        this.inputFocused = true;
        // we need this because nothing will 
        // happens on next method call, 
        // ngOnChanges in directive is only called if value is changed,
        // so we have to reset this value in async way,
        // this is ugly but works
        setTimeout(() => {this.inputFocused = false});
    }
}

Solution with EventEmitter

To solve the problem with setTimeout(() => {this.inputFocused = false}); We can bind our directive for events source - EventEmitter, or to Observable. Below is an example of EventEmitter usage.

// Directive
import {Directive, EventEmitter, Input, ElementRef} from 'angular2/core';

@Directive({
    selector: '[focus]'
})
class FocusDirective {
    private focusEmitterSubscription;   
    // Now we expect EventEmitter as binded value
    @Input('focus')
    set focus(focusEmitter: EventEmitter) {
        if(this.focusEmitterSubscription) {
            this.focusEmitterSubscription.unsubscribe();
        }
        this.focusEmitterSubscription = focusEmitter.subscribe(
            (()=> this.element.nativeElement.focus()).bind(this))
    }    
    constructor(@Inject(ElementRef) private element: ElementRef) {}
}

// Usage
@Component({
    selector : 'app',
    template : `
        <input [focus]="inputFocused" type="text">
        <button (click)="moveFocus()">Move Focus</button>
    `,
    directives: [FocusDirective]
})
class App {
    private inputFocused = new EventEmitter();
    moveFocus() {
        this.inputFocused.emit(null);    
    }
}

Both solutions solves your problem, but second has a little better performance and looks nicer.

Answer 3

Actually you don't need to write any TS code for that (I'm using one of the other answer's example):

<input (keyup.enter)="focusable.focus()"/>
<input #focusable /> 

Answer 4

Set focus - Angular 2/5

<input type="text" [(ngModel)]="term2" #inputBox>

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

@Component({
  selector: 'app-general',
  templateUrl: './general.component.html',
  styleUrls: ['./general.component.scss']
})
export class GeneralComponent {

  @ViewChild("inputBox") _el: ElementRef;

  setFocus() {
    this._el.nativeElement.focus();
  }
}

For setting focus on load

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

You can update this logic accordingly for key press.

More Info