animatedswitcher.dart

class _ClickCounterState extends State<ClickCounter> {
  int _count = 0;
  var keys = [1, 2, 3];
  var colors = [Colors.red, Colors.blue, Colors.green];
  var borderRadius = [50.0, 30.0, 0.0];
  
  Widget createBox(int key) => Container(
    decoration: BoxDecoration(
      color: colors[key],
      borderRadius: BorderRadius.circular(borderRadius[key]),
    ),
    width: 200.0,
    height: 100.0,
    key: ValueKey<int>(key),
  );

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Material(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            AnimatedSwitcher(
              duration: const Duration(milliseconds: 500),
              transitionBuilder: (Widget child, Animation<double> animation) {
                return ScaleTransition(child: child, scale: animation);
              },
              child: createBox(_count),
            ),
            Container(height: 200.0),
            RaisedButton(
              child: const Text('Switch'),
              onPressed: () {
                setState(() {
                  if(_count > 1) {
                    _count = 0;
                  } else {
                    _count++;
                  }
                });
              },
            ),
          ],
        ),
      ),
    );
  }
}