Flutter: restart SlideAnimation from current object position - animation

Question

I've got a SlideAnimation on an object that get's triggered every time I tap the screen. The object simply slides up atm but when I tap the screen again the animation starts from the original position of the object again. How would I capture the position the object ended in the last animation and perform the animation from there on?
I've got the following code for the creating of the SlideTransition:
new SlideTransition(
child: new Container(
child: char,
),
position: _characterPosition,
)
And this code for the actual animation:
_characterPosition = new FractionalOffsetTween(
begin: const FractionalOffset(0.0, 0.0),
end: const FractionalOffset(0.0, -0.2),
).animate(new CurvedAnimation(
parent: _characterAnimationController,
curve: Curves.easeOut,
)
);

Answer 1

In the simplest case you can use your _characterAnimationController. AnimationController has two related methods stop and forward. Verify current animation's state and invoke required method:
void _onTap() {
if (_characterAnimationController.isAnimating) {
_characterAnimationController.stop(canceled: false);
} else {
_characterAnimationController.forward();
}
}
To extend animation after completion you can reset _characterAnimationController state via value(or create new one) and update position. Complete example:
class Home extends StatefulWidget {
#override
State createState() => new _HomeState();
}
class _HomeState extends State<Home> with TickerProviderStateMixin {
Animation _characterPosition;
AnimationController _characterAnimationController;
FractionalOffset _beginOffset;
FractionalOffset _endOffset;
FractionalOffset _animationOffset;
void _restartAnimation() {
_characterAnimationController.value = 0.0;
_beginOffset = _endOffset;
_endOffset = _endOffset + _animationOffset;
setState(() {
_characterPosition = _generateCharacterPosition();
});
_characterAnimationController.forward();
}
#override
void initState() {
_animationOffset = const FractionalOffset(0.0, 0.15);
_beginOffset = const FractionalOffset(0.0, 0.0);
_endOffset = _animationOffset;
_characterAnimationController = new AnimationController(
duration: new Duration(seconds: 5), vsync: this);
_characterPosition = _generateCharacterPosition();
}
#override
Widget build(BuildContext context) {
return new Material(
child: new InkWell(
child: new SlideTransition(
child: new Container(
child: new Text("Hello"),
),
position: _characterPosition,
),
onTap: _onTap,
),
);
}
void _onTap() {
if (_characterAnimationController.isAnimating) {
_characterAnimationController.stop(canceled: false);
} else if (_characterAnimationController.status ==
AnimationStatus.completed) {
_restartAnimation();
} else {
_characterAnimationController.forward();
}
}
Animation _generateCharacterPosition() => new FractionalOffsetTween(
begin: _beginOffset,
end: _endOffset,
)
.animate(new CurvedAnimation(
parent: _characterAnimationController,
curve: Curves.easeOut,
));
}