How to Achieve Smooth CSS Transitions with Angular 2\'s ngIf?

Angular 2 ngIf and CSS Transition/Animation: Resolving Transition Issues

With ngIf, it's common to encounter challenges when attempting CSS transitions on elements controlled by the directive. ngIf removes elements from the DOM when its condition becomes false, hindering the ability to apply transitions.

Original Issue

When using ngIf with CSS transitions, the element is hidden initially and transitions won't work.

Solution

Since ngIf removes elements from the DOM, an alternative approach is to use the hidden attribute instead.

Code Sample

<code class="html"><div class="note" [ngClass]="{'transition':show}" [hidden]="!show">
    <p> Notes</p>
</div></code>

Alternatively, with Angular 4.1.0 and above

Angular animations provide an elegant way to handle such transitions.

Code Sample

<code class="typescript">import { trigger, style, animate, transition } from '@angular/animations';

@Component({
    animations: [
        trigger(
            'enterAnimation', [
                transition(':enter', [
                    style({transform: 'translateX(100%)', opacity: 0}),
                    animate('500ms', style({transform: 'translateX(0)', opacity: 1}))
                ]),
                transition(':leave', [
                    style({transform: 'translateX(0)', opacity: 1}),
                    animate('500ms', style({transform: 'translateX(100%)', opacity: 0}))
                ])
            ]
        )
    ],
    template: `
        <button (click)="show = !show">toggle show ({{show}})</button>

        <div *ngIf="show" [@enterAnimation]>xxx</div>
    `
})
export class App {
    show: boolean = false;
}</code>

Advantages of Using Animations

• Angular animations allow for precise control over the transition timeline and easing functions.
• They handle both entering and leaving transitions seamlessly.
• Maintainability and readability of CSS code is improved by separating transition logic into a separate component.

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