flutter setState isn't defined - flutter

Question

I have a Widget to create a sidebar menu:
Widget dashboard(context) {
return Material(
elevation: 8,
color: backgroundColor,
child: Container(
padding: const EdgeInsets.only(left: 16, right: 16, top: 48),
child: Column(
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
mainAxisSize: MainAxisSize.max,
children: [
InkWell(child: Icon(Icons.menu, color: Colors.white), onTap: () {
setState(() {
isCollapsed = !isCollapsed;
});
},),
Text("Corona App", style: TextStyle(fontSize: 24.0, color: Colors.white)),
Icon(Icons.settings, color: Colors.white),
])
],
),
)
);
}
But I keep getting the error that my setState function isn't defined. My main app is a statefullwidget so this is pretty weird. Can anyone help me?
Here is the full code!
import 'package:flutter/material.dart';
final Color backgroundColor = Color(0xFF4A4A58);
class MenuDashboard extends StatefulWidget {
#override
_MenuDashboardState createState() => _MenuDashboardState();
}
class _MenuDashboardState extends State<MenuDashboard> {
bool isCollapsed = true;
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: backgroundColor,
body: Stack(
children: <Widget>[
menu(context),
dashboard(context),
],
),
);
}
}
Widget menu(context) {
return Padding(
padding: const EdgeInsets.only(left: 16.0),
child: Align(
alignment: Alignment.centerLeft,
child: Column(
mainAxisSize: MainAxisSize.min,
mainAxisAlignment: MainAxisAlignment.spaceAround,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text("Home", style: TextStyle(color: Colors.white, fontSize: 20),),
SizedBox(height: 10.0),
Text("Brochures", style: TextStyle(color: Colors.white, fontSize: 20),),
SizedBox(height: 10.0),
Text("Visitekaartje", style: TextStyle(color: Colors.white, fontSize: 20),),
SizedBox(height: 10.0),
]
)
)
);
}
Widget dashboard(context) {
return Material(
elevation: 8,
color: backgroundColor,
child: Container(
padding: const EdgeInsets.only(left: 16, right: 16, top: 48),
child: Column(
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
mainAxisSize: MainAxisSize.max,
children: [
InkWell(child: Icon(Icons.menu, color: Colors.white), onTap: () {
setState(() {
isCollapsed = !isCollapsed;
});
},),
Text("Corona App", style: TextStyle(fontSize: 24.0, color: Colors.white)),
Icon(Icons.settings, color: Colors.white),
])
],
),
)
);
}
with the error message: 'The function setState isn't defined'

Answer 1

setState is a member of State class, which means it can only be called inside a class that extends a State class of a StatefulWidget. If your class is extending StatelessWidget, you can't called state members/methods provided by the super class, including setState, initState and dispose methods.
For the answer, you can't call setState outside of the State class, if possible, put the widget methods inside the class, or pass setState function as a parameter to those methods.

Answer 2

setState can only called inside StatefulWidget. So if I got it right, you use setState in Widget dashboard or menu widgets. It can't work, because those widgets in outside of class. Try to put widgets inside the class