minimal_example.dart

bool isVisible = true;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Animated Switcher")),
      floatingActionButton: FloatingActionButton(onPressed: () {
        setState(() {
          isVisible = !isVisible;
        });
      }),
      body: Center(
        child: AnimatedSwitcher(
        child: isVisible
            ? Container(
                height: 100.0,
                width: 100.0,
                color: Colors.red,
              )
            : SizedBox(),
        duration: Duration(seconds: 2),
      )),
    );
  }