Add class to an element in Angular 4

Question

I was trying to create an image gallery with Angular 4.The logic behind this is to add a Cascading Style Sheet (CSS) class to the selected image that will show a red border on the selected (clicked) image. This is the CSS stylesheet for an image gallery.

I want to show a red selection square on the image I have clicked. this-is-a-class should be added to the selected image.

#container{
  border:1px solid red;
  height:auto;
}

ul li{
  margin-right:20px;
  margin-left:0;
  list-style-type:none;
  display:inline;
}

ul li img{
  width: 200px;
  height:200px;
  border:1px solid grey;
}

#select{
  border:2px solid violet;
}

.this-is-a-class{
  border: 10px solid red !important;
}

following is the template code

<div id="container">
  <ul>
    <li><img class="this-is-a-class" id="1" src="../../assets/images/1.jpg" (click)="addClass(id=1)"/></li>
    <li><img id="select" src="../../assets/images/2.png" (click)="addClass(id=2)"/></li>
    <li><img id="3" src="../../assets/images/3.jpg" (click)="addClass(id=3)"/></li>
    <li><img id="4" src="../../assets/images/4.png" (click)="addClass(id=4)"/></li>
    <li><img id="5" src="../../assets/images/5.jpg" (click)="addClass(id=5)"/></li>
  </ul>
</div>

<div>
  <h1>You Clicked on: {{id}}</h1>
</div>

The component code is as follows

import { Component, OnInit } from '@angular/core';
import { DataService } from '../../services/data.service';

@Component({
  selector: 'app-user',
  templateUrl: './user.component.html',
  styleUrls: ['./user.component.css']
})

export class UserComponent implements OnInit {
  id: number;
  constructor() {
    console.log("Constructor working..")

  }

  ngOnInit() {
    console.log('ngOnInit works..');
  }

  //function to add the class to selected image to show the border.
  addClass(id) {
    this.id = id;
    //id = this.id? 'selectedImg' : 'null';
  }
}

Answer 1

Use [ngClass] and conditionally apply class based on the id.

In your HTML file:

<li>
    <img [ngClass]="{'this-is-a-class': id === 1 }" id="1"  
         src="../../assets/images/1.jpg" (click)="addClass(id=1)"/>
</li>
<li>
    <img [ngClass]="{'this-is-a-class': id === 2 }" id="2"  
         src="../../assets/images/2.png" (click)="addClass(id=2)"/>
</li>

In your TypeScript file:

addClass(id: any) {
    this.id = id;
}

Answer 2

Here is a plunker showing how you can use it with the ngClass directive.

I'm demonstrating with divs instead of imgs though.

Template:

<ul>
      <li><div [ngClass]="{'this-is-a-class': selectedIndex == 1}" (click)="setSelected(1)"> </div></li>
      <li><div [ngClass]="{'this-is-a-class': selectedIndex == 2}" (click)="setSelected(2)"> </div></li>
      <li><div [ngClass]="{'this-is-a-class': selectedIndex == 3}" (click)="setSelected(3)"> </div></li>
</ul>

TS:

export class App {
  selectedIndex = -1;

  setSelected(id: number) {
    this.selectedIndex = id;
  }
}

Answer 3

If you want to set only one specific class, you might write a TypeScript function returning a boolean to determine when the class should be appended.

TypeScript

function hideThumbnail():boolean{
    if (/* Your criteria here */)
        return true;
}

CSS:

.request-card-hidden {
    display: none;
}

HTML:

<ion-note [class.request-card-hidden]="hideThumbnail()"></ion-note>

Answer 4

If you need that each div will have its own toggle and don't want clicks to affect other divs, do this:

Here's what I did to solve this...

<div [ngClass]="{'teaser': !teaser_1 }" (click)="teaser_1=!teaser_1">
...content...
</div>

<div [ngClass]="{'teaser': !teaser_2 }" (click)="teaser_2=!teaser_2">
...content...
</div>

<div [ngClass]="{'teaser': !teaser_3 }" (click)="teaser_3=!teaser_3">
...content...
</div>

it requires custom numbering which sucks, but it works.

Answer 5

2024 answer:

Inject renderer2:

import { Renderer2 } from '@angular/core';

constructor(private renderer: Renderer2) { }

Then pass in the element reference the new class will be added to and the class name:

this.renderer.addClass(this.myButton.nativeElement, 'copied');

Answer 6

you can try this without any java script you can do that just by using CSS

img:active,
img:focus,
img:hover{ 
border: 10px solid red !important
}

of if your case is to add any other css class by clicking you can use query selector like

<img id="image1" ng-click="changeClass(id)" >
<img id="image2" ng-click="changeClass(id)" >
<img id="image3" ng-click="changeClass(id)" >
<img id="image3" ng-click="changeClass(id)" >

in controller first search for any image with red border and remove it then by passing the image id add the border class to that image

$scope.changeClass = function(id){
angular.element(document.querySelector('.some-class').removeClass('.some-class');
angular.element(document.querySelector(id)).addClass('.some-class');
}