Angular2 on focus event to add class

问题

I'm looking to update an Angular 1 app to Angular 2 and am having an issue with one of my old directives.

The idea is simple. When an input field is focused a class should be added (md-input-focus) and another be removed (md-input-wrapper). Then this process should be reversed on "blur" event - i.e. focus lost.

My old directive simply included the lines

.directive('mdInput',[
    '$timeout',
    function ($timeout) {
        return {
            restrict: 'A',
            scope: {
                ngModel: '='
            },
            link: function (scope, elem, attrs) {
                var $elem = $(elem);
                $elem.on('focus', function() {
                      $elem.closest('.md-input-wrapper').addClass('md-input-focus')
                })
                .on('blur', function() {
                 $(this).closest('.md-input-wrapper').removeClass('md-input-focus');
                })
             }

etc...

I obviously have the classic start to my directive but have run out of.....skill

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

@Directive({
      selector: '.mdInput',

})

export class MaterialDesignDirective {
      constructor(el: ElementRef, renderer: Renderer) {
           // Insert inciteful code here to do the above
      }
}

Any help would be appreciated.

UPDATE:

The HTML would look like (before the input element was focused):

<div class="md-input-wrapper">
   <input type="text" class="md-input">
</div>

and then

<div class="md-input-wrapper md-input-focus">
   <input type="text" class="md-input">
</div>

after.

The input element is the only one which can receive a focus event (and therefore the target for the directive) however the parent <div> requires the class addition and removal.

Further help

Please see Plunker for help/explanation - would be great if someone could help

回答1:

Update

@Directive({selector: '.md-input', host: {
  '(focus)': 'setInputFocus(true)',
  '(blur)': 'setInputFocus(false)',
}})
class MaterialDesignDirective {
  MaterialDesignDirective(private _elementRef: ElementRef, private _renderer: Renderer) {}
  setInputFocus(isSet: boolean): void {
    this.renderer.setElementClass(this.elementRef.nativeElement.parentElement, 'md-input-focus', isSet);
  }
}

Original

This can easily be done without ElementRef and Renderer (what you should strive for in Angular2) by defining host bindings:

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

@Directive({
      selector: '.mdInput',
      host: {
        '(focus)':'_onFocus()',
        '(blur)':'_onBlur()',
        '[class.md-input-focus]':'inputFocusClass'
      }

})

export class MaterialDesignDirective {
      inputFocusClass: bool = false;

      _onFocus() {
        this.inputFocusClass = true;
      }

      _onBlur() {
        this.inputFocusClass = false;
      }
}

or a bit more terse

@Directive({
      selector: '.mdInput',
      host: {
        '(focus)':'_setInputFocus(true)',
        '(blur)':'_setInputFocus(false)',
        '[class.md-input-focus]':'inputFocusClass'
      }

})

export class MaterialDesignDirective {
      inputFocusClass: bool = false;

      _setInputFocus(isFocus:bool) {
        this.inputFocusClass = isFocus;
      }
}

I tried it only in Dart where it works fine. I hope I translated it correctly to TS.

Don't forget to add the class to the directives: of the element where you use the directive.

回答2:

In addition to previous answers, if you don't want to add a directive, for the specific component (you already have a directive for a parent component, you are using Ionic 2 page or something else), you inject the renderer by adding private _renderer: Renderer in the page constructor and update the element using the event target like this:

html:

(dragstart)="dragStart($event)"

TS:

dragStart(ev){
    this._renderer.setElementClass(ev.target, "myClass", true)
}

Edit: to remove the class just do:

dragEnd(ev){
    this._renderer.setElementClass(ev.target, "myClass", false)
}

回答3:

The name of the selector has to be inside "[ ]", as shown below

@Directive({
  selector: '[.mdInput]',
  host: {
    '(focus)':'_setInputFocus(true)',
    '(blur)':'_setInputFocus(false)',
    '[class.md-input-focus]':'inputFocusClass'
  }
})

回答4:

If you want to catch the focus / blur events dynamiclly on every input on your component :

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

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: [ './app.component.css' ]
})
export class AppComponent implements AfterViewInit {
  name = 'Angular focus / blur Events';

  constructor(private el: ElementRef) {
  }

  ngAfterViewInit() {
       // document.getElementsByTagName('input') : to gell all Docuement imputs
       const inputList = [].slice.call((<HTMLElement>this.el.nativeElement).getElementsByTagName('input'));
        inputList.forEach((input: HTMLElement) => {
            input.addEventListener('focus', () => {
                input.setAttribute('placeholder', 'focused');
            });
            input.addEventListener('blur', () => {
                input.removeAttribute('placeholder');
            });
        });
    }
}

Checkout the full code here : https://stackblitz.com/edit/angular-wtwpjr

来源：https://stackoverflow.com/questions/34799667/angular2-on-focus-event-to-add-class