How to hot-reload State fields? - flutter

Question

How to hot-reload fields of a State subclass in Flutter?
I know that the modifying the initial value of fields isn't taken into account during hot-reload and that I can use hot-restart for them. But this is painfully slow.
Is there any way to ease the process?
A typical use-case would be animations, especially AnimationController. As it is stored inside a State field, but we usually want to iterate over its duration. Example:
class MyAnim extends StatefulWidget {
#override
_MyAnimState createState() => _MyAnimState();
}
class _MyAnimState extends State<MyAnim> with SingleTickerProviderStateMixin {
AnimationController animationController;
#override
void initState() {
animationController =
AnimationController(vsync: this, duration: const Duration(seconds: 1));
super.initState();
}
#override
void dispose() {
animationController.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return Container();
}
}

Answer 1

State provides a custom lifecycle hook for hot-reloads: reassemble
You can freely override that method to have custom hot-reload behaviors. Don't worry, this method will never be called in production.
With a small tweak you'd get the following:
class _MyAnimState extends State<MyAnim> with SingleTickerProviderStateMixin {
AnimationController animationController;
#override
void initState() {
animationController = AnimationController(vsync: this);
_initializeFields();
super.initState();
}
void _initializeFields() {
animationController.duration = const Duration(seconds: 1);
}
#override
void reassemble() {
_initializeFields();
super.reassemble();
}
#override
void dispose() {
animationController.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return Container();
}
}
Now, whenever you modify your State class, it will correctly update AnimationController's duration.