How to run animation backwards when its finished - flutter

Question

I have this simple animation of a line that goes from bottom to top of my container:
void didChangeDependencies() {
animationController = AnimationController(duration: const Duration(seconds: 2), vsync: this);
double firstPosition = (MediaQuery.of(context).size.height / 2) - (MediaQuery.of(context).size.width / 2);
double lastPosition = (firstPosition + MediaQuery.of(context).size.width * proporcaoScaner) - (espessuraContornos + esperruraLinha);
animation = Tween<double>(begin: firstPosition, end: lastPosition).animate(animationController)
..addListener(() {
setState(() {});
});
animationController.forward();
And I want it to run backwards once it reach the lastPosition, I tried animationController.repeat() but it just jump back to first position. I've also tried to make it conditional:
if (animationController.isCompleted) {
animationController.reverse();
} else {
animationController.forward();
}
But it just stops on lastPosition.

Answer 1

This code is working, but I don't know it its the best aproach.
void didChangeDependencies() {
animationController = AnimationController(duration: const Duration(seconds: 2), vsync: this);
double firstPosition = (MediaQuery.of(context).size.height / 2) - (MediaQuery.of(context).size.width / 2);
double lastPosition = (firstPosition + MediaQuery.of(context).size.width * proporcaoScaner) - (espessuraContornos + esperruraLinha);
animation = Tween<double>(begin: firstPosition, end: lastPosition).animate(animationController);
animationController.addListener(() {
if (animationController.isCompleted) {
setState(() {
animationController.reverse();
});
}
if (animationController.isDismissed) {
setState(() {
animationController.forward();
});
}
setState(() {
});
});
animationController.forward();
super.didChangeDependencies();
}