Can an AnimatedContainer animate its height?

Question

I'd like to animate a gap between two items in a list. I thought of using an AminatedContainer with a height initially at zero but I'm not familiar with how to make this work. My code at the moment is:

    new AnimatedContainer(
      duration: const Duration(milliseconds: 200),
      height: App.itemSelected==id ? 50.0 : 0.0,
      curve: Curves.fastOutSlowIn,
    ),

That does change the height of the Container but not in an animated way as I had hoped. Any help would be gratefully received!

Answer 1

You can use an AnimatedSize for that purpose.

https://docs.flutter.io/flutter/widgets/AnimatedSize-class.html

Answer 2

I am not sure if AnimatedSize is suitable for your use case, but I have added an example on how to make a simple animation with it:

The coloring is a bit off due to the recording but you should be able to test this yourself.

class MyAppState extends State<MyApp> with TickerProviderStateMixin {
  double _height = 50.0;
  double _width = 20.0;
  var _color = Colors.blue;

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        body: new Center(
          child: new Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              new AnimatedSize(

                curve: Curves.fastOutSlowIn, child: new Container(
                width: _width,
                height: _height,
                color: _color,
              ), vsync: this, duration: new Duration(seconds: 2),),
              new Divider(height: 35.0,),
              new Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  new IconButton(
                      icon: new Icon(Icons.arrow_upward, color: Colors.green,),
                      onPressed: () =>
                          setState(() {
                            _color = Colors.green;
                            _height = 95.0;
                          })),
                  new IconButton(
                      icon: new Icon(Icons.arrow_forward, color: Colors.red,),
                      onPressed: () =>
                          setState(() {
                            _color = Colors.red;
                            _width = 45.0;
                          })),
                ],
              )
            ],)
          ,)
    );
  }
}