How to Animate Elements Controlled by ngIf in Angular 2?

Angular 2 ngIf and CSS Transitions/Animations

This question delves into the challenges of performing CSS transitions or animations on elements manipulated by the ngIf directive in Angular 2.

Issue

The goal is to animate the entrance of an element from the right using CSS. However, when ngIf is used to initially hide the element, the transition fails to trigger.

Solution

The key issue lies in the behavior of ngIf. When the expression associated with ngIf becomes false, the element is removed from the DOM. Since transitions and animations require the element to be present in the DOM, applying them to an element that is not rendered will not work.

To address this issue, the suggestion is to use hidden instead of ngIf to hide the element initially.

Updated Solution (Angular 4.1.0 and above)

In Angular 4.1.0 and later versions, the preferred approach is to use Angular animations. Here's an updated solution using animations:

<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 }))
        ])
      ]
    )
  ]
})

// ...

<div *ngIf="show" [@enterAnimation]></div></code>

This solution adds a trigger to the component called 'enterAnimation' and defines transitions for both enter and leave states. The transition includes styling for transform and opacity, allowing the element to slide in from the right with animation.

Remember, this solution is applicable for Angular 4.1.0 and above. For older versions, using hidden remains the recommended approach.

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