Is it possible to animate mat-tree? (Angular Material)

Question

I am using mat-tree (https://material.angular.io/components/tree/overview) from Angular Materials. When expanding a parent-tree-node, I want to animate the appearance and disappearance of the child-tree-nodes. Here is an example of how I would like the animation to be:

I know that Angular is offering a feature for animations, but yet I couldn't find out how to animate mat-tree.

Is it possible to animate mat-tree of Angular Material? Or am I forced to code my own tree-menu if I want that kind of animation?

Answer 1

Following the method in the accepted answer to do this with an animation of the child nodes sliding in/out vertically you can use a nested tree. Stackblitz

Add the animation to the component:

  @Component({
    selector: 'tree-nested-overview-example',
    templateUrl: 'tree-nested-overview-example.html',
    styleUrls: ['tree-nested-overview-example.css'],
    animations:[
          trigger('slideVertical', [
        state(
          '*',
          style({
            height: 0
          })
        ),
        state(
          'show',
          style({
            height: '*'
          })
        ),
        transition('* => *', [animate('400ms cubic-bezier(0.25, 0.8, 0.25, 1)')])
      ])
    ]
  })

Apply the animation to the element containing the child nodes:

<mat-nested-tree-node *matTreeNodeDef="let node; when: hasChild">
  <li>
    <div class="mat-tree-node">
      <button mat-icon-button matTreeNodeToggle
              [attr.aria-label]="'toggle ' + node.name">
        <mat-icon class="mat-icon-rtl-mirror">
          {{treeControl.isExpanded(node) ? 'expand_more' : 'chevron_right'}}
        </mat-icon>
      </button>
      {{node.name}}
    </div>
    <ul  [@slideVertical]="treeControl.isExpanded(node) ? 'show' : null">
      <ng-container matTreeNodeOutlet></ng-container>
    </ul>
  </li>
</mat-nested-tree-node>

Hide the overflow on the element:

.example-tree ul {
  overflow: hidden;
}