Angular 2 Slide Up and Down Animation

Question

I recently built the following Angular 2 Read More component. What this component does is collapse and expand long blocks of text with \"Read more\" and \"Read Less\" links.

Answer 1

Automatic property calculation

Animation with automated height calculation

Sometimes you don't know the value of a dimensional style property until runtime. For example, elements often have widths and heights that depend on their content and the screen size. These properties are often tricky to animate with CSS.

In these cases, you can use a special * property value so that the value of the property is computed at runtime and then plugged into the animation.

In this example, the leave animation takes whatever height the element has before it leaves and animates from that height to zero :

animations: [
  trigger('shrinkOut', [
    state('in', style({height: '*'})),
    transition('* => void', [
      style({height: '*'}),
      animate(250, style({height: 0}))
    ])
  ])
]

from Angular official documentation (now as an archive) : https://v2.angular.io/docs/ts/latest/guide/animations.html#!#automatic-property-calculation

Answer 2

My Solution with :enter, :leave and *ngIf:

@Component({
    selector: 'accordion',
    templateUrl: './accordion.component.html',
    animations: [
        trigger('slideInOut', [
            state('in', style({height: '*', opacity: 0})),
            transition(':leave', [
                style({height: '*', opacity: 1}),

                group([
                    animate(300, style({height: 0})),
                    animate('200ms ease-in-out', style({'opacity': '0'}))
                ])

            ]),
            transition(':enter', [
                style({height: '0', opacity: 0}),

                group([
                    animate(300, style({height: '*'})),
                    animate('400ms ease-in-out', style({'opacity': '1'}))
                ])

            ])
        ])
    ]
})
...

Template:

<div *ngIf="shown" [@slideInOut] >
    // ...content
</div>

Unfortunately I had to incorporate this fix also (for slideOut): https://github.com/angular/angular/issues/15798

Answer 3

This is what I use in Angular 8.1.2. The beauty of the code is that it supports unlimited height of the div that needs to be shown/collapsed and also makes smooth transitions.

TS FILE:

import {Component, OnInit} from '@angular/core';
import {trigger, transition, animate, style, state} from '@angular/animations';

@Component({
    selector: 'app-all-data',
    templateUrl: './all-data.page.html',
    styleUrls: ['./all-data.page.scss'],
    animations: [
        trigger('openClose', [
            state('open', style({
                height: '*',
                opacity: 1,
            })),
            state('closed', style({
                height: '0',
                opacity: 0
            })),
            transition('open => closed', [
                animate('0.35s')
            ]),
            transition('closed => open', [
                animate('0.35s')
            ]),
        ]),
    ]
})
export class AllDataPage implements OnInit {

    showCardBody = false;

    constructor() {
    }

    ngOnInit() {
    }

    /**
     * Toggle details on click
     */
    showDetails() {
        this.showCardBody = !this.showCardBody;
    }

}

HTML FILE:

<button type="button" (click)="showDetails()">
       Toggle Details
</button>

<div class="card-body" [@openClose]="showCardBody ? 'open' : 'closed'">
       <p>This is some content</p>
       <p>This is some content</p>
       <p>This is some content</p>       
       <p>This is some content</p>
       <p>This is some content</p>
</div>

Answer 4

Threeve's answer is correct - the only problem is that the CSS transition will not work with 'auto'. So you need to capture the auto height in the ngAfterViewInit function and store it as a string. Notice also the use of the setTimeout function to stop the 'unidirectional-data-flow-violation error' that can occur.

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

@Component({
selector: 'read-more',
template: `
    <div [style.height]="isCollapsed ? maxHeight+'px' : autoHeight">
        <ng-content></ng-content>
    </div> 

    <span *ngIf="isCollapsable" class="btn-link cpointer" (click)="isCollapsed =! isCollapsed">Read {{isCollapsed? 'more':'less'}} ...</span>

    `,
styles: [` div { overflow-y: hidden; 
          -moz-transition: height .5s;
          -ms-transition: height .5s;
          -o-transition: height .5s;
          -webkit-transition: height .5s;
          transition: height .5s; ease;}
         .cpointer {cursor:pointer; }
        `]
})
export class ReadMoreComponent implements AfterViewInit {

@Input()
maxHeight: number = 40; //two lines

////set these to false to get the height of the expended container 
isCollapsed: boolean = false;
isCollapsable: boolean = false;
autoHeight: string= "auto";

constructor(private elementRef: ElementRef) {}

ngAfterViewInit() {
    // Inportant !!
    // wait a tick to avoid one-time devMode
    // unidirectional-data-flow-violation error
    setTimeout(_ => {
            let currentHeight = this.elementRef.nativeElement.getElementsByTagName('div')[0].offsetHeight;

            this.autoHeight = currentHeight + "px";
            //collapsable only if the contents make container exceed the max height
            if (currentHeight >= this.maxHeight) {
                this.isCollapsed = true;
                this.isCollapsable = true;
            }
        }
    );
}

}