@override

Widget build(BuildContext context) {
    return

AnimatedBuilder(

builder: _buildAnimation,
      animation: controller,
    );
  }
}

Stateful widget: StaggerDemo

The stateful widget, StaggerDemo, creates the AnimationController
(the one who rules them all), specifying a 2000 ms duration. It plays
the animation, and builds the non-animating portion of the widget tree.
The animation begins when a tap is detected in the screen.
The animation runs forward, then backward.

class StaggerDemo extends StatefulWidget {
  @override
  _StaggerDemoState createState() => _StaggerDemoState();
}

class _StaggerDemoState extends State<StaggerDemo> with TickerProviderStateMixin {
  AnimationController _controller;

  @override
  void initState() {
    super.initState();