How to access attributes of the widgets children - flutter

Question

I am opening a new activity with the startTimer method How do I set the cyclesVal variable to an attribute of my custom NumberSelector widget so I can pass it to the next activity. Any way to access an internal variable of the NumberSelector widget would work too since I have set the attribute to the variable.
class ExcersizeInput extends StatelessWidget {
const ExcersizeInput({super.key});
void startTimer(BuildContext context) {
int cyclesVal = 1;
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => TimerPage(
cycleCount: cyclesVal,
),
));
}
#override
Widget build(BuildContext context) {
return Column(children: [
Column(
children: [
NumberSelector(
title: "Cycles",
),
],
),
ElevatedButton.icon(
onPressed: (() => {startTimer(context)}),
label: const Text("Start"),
icon: const Icon(Icons.start_outlined),
)
]);
}
}
Here's the NumberSelector code:
class NumberSelector extends StatefulWidget {
final String title;
const NumberSelector(
{super.key, required this.title});
#override
State<NumberSelector> createState() => _NumberSelectorState();
}
class _NumberSelectorState extends State<NumberSelector> {
int selectorValue = 1;
void updateValue(ifAdd) {
setState(() {
if (ifAdd) {
if (selectorValue < 9999) {
selectorValue++;
}
} else {
if (selectorValue > 1) {
selectorValue--;
}
}
});
}
#override
Widget build(BuildContext context) {
final ColorScheme colors = Theme.of(context).colorScheme;
return Column(
children: [
Text(widget.title,
style: const TextStyle(fontSize: 20, fontWeight: FontWeight.bold)),
Row(
children: [
GestureDetector(
child: IconButton(
onPressed: () => updateValue(false),
icon: const Icon(Icons.remove),
style: styleContainedButton),
},
),
Text(selectorValue.toString()),
style: const TextStyle(fontSize: 16)),
GestureDetector(
child: IconButton(
onPressed: () => updateValue(true),
icon: const Icon(Icons.add),
style: styleContainedButton),
},
),
],
),
],
);
}
}

Answer 1

To get a variable from a stateful widget in flutter it needs a key that is linked to the state of the widget. Via the key, the variables can be accessed.
Define a widget you want to access from its parent and that contains any value:
class TestWidget extends StatefulWidget {
TestWidget({Key? key}) : super(key: key);
#override
State<TestWidget> createState() => TestWidgetState();
}
class TestWidgetState extends State<TestWidget> {
int? anyvalue;
#override
Widget build(BuildContext context) {
return Container();
}
}
Declare the key in the parent widget. Make sure the name of the state does not start with an underscore:
GlobalKey<TestWidgetState> _widget_key = GlobalKey();
Give the key to the widget in the build method of the parent widget:
TestWidget(
key: _widget_key,
)
Now the value of the child widget can be accessed in the parent widget via the key:
void afunction() {
print(_widget_key.currentState!.anyvalue);
}