animate method
Implementation
Future<void> animate({Duration? duration, Curve curve = Curves.linear}) {
assert(!_controller.isAnimating, 'cannot animate until current animation is complete');
var update = false;
for (final value in _data.values) update |= value.update();
if (update) {
_controller.value = _controller.lowerBound;
return _controller.animateTo(_controller.upperBound, duration: duration, curve: curve);
}
return Future.value();
}