Rotate icon 180 degree with animation in flutter

Question

I have a IconButton, Normally, It's icon is Icons.expand_more but When I press that its icon should be Icons.expand_less. I want to animated this so that if I press that button, it will rotate and point the downwords from upwords. and same when I press the expand_less then it should become expand_more with rotating animation. How can I acheive this ? below is my code :

    IconButton(
      icon:  _expanded ? Icon(Icons.expand_less) : Icon(Icons.expand_more),
      onPressed: () {
        setState(() {
           _expanded = !_expanded;
        });
      },
   )

I tried to use animatedContainer but it didn't work as I am using two different icons and that rotation effect I cannot acheive with this. I also tried to rotate the icon with below approach but it cannot show the animation when it is rotating from 0 to 180 degree.

IconButton(
              icon: AnimatedContainer(
                  duration: Duration(seconds: 3),
                  child: Transform.rotate(
                      angle: _expanded ? 0 : 180 * math.pi / 180,
                      child: Icon(Icons.expand_less))),
              // icon:
              //     _expanded ? Icon(Icons.expand_less) : Icon(Icons.expand_more),
              onPressed: () {
                setState(() {
                  _expanded = !_expanded;
                });
              },
            )

This is before expansion :

This is after expansion :

I want the rotation animation on button click.

Answer 1

Thanks to @krumpli.

1. Define AnimationController _controller.

2. Define init method as :

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

    _controller = AnimationController(
      vsync: this,
      duration: Duration(milliseconds: 300),
      upperBound: 0.5,
    );
  }

3. Define dispose method as :

@override
  void dispose() {
    super.dispose();
    _controller.dispose();
  }

4. With the use of the widget RotationTransition :

RotationTransition(
              turns: Tween(begin: 0.0, end: 1.0).animate(_controller),
              child: IconButton(
                icon: Icon(Icons.expand_less),
                onPressed: () {
                  setState(() {
                    if (_expanded) {
                      _controller..reverse(from: 0.5);
                    } else {
                      _controller..forward(from: 0.0);
                    }
                    _expanded = !_expanded;
                  });
                },
              ),
            )

Don't forget to add with SingleTickerProviderStateMixin in the class defintion.