How can I make an Expandable Panel editable? - flutter

Question

I'm new to flutter and I'm currently working on an app for my school project. At the moment I cannot make my expanded panel editable, could anybody tell me how I can make something editable or if it's not possible tell me an alternativ solution? Here's the code btw.:
class MyItem {
MyItem({this.isExpanded = false, required this.header, required this.body});
bool isExpanded;
final String header;
final String body;
}
class fourthPage extends StatefulWidget {
#override
list createState() => list();
}
class list extends State<fourthPage> {
final List<MyItem> _items = <MyItem>[
MyItem(
header: "header1",
body: "text1"),
MyItem(
header: "header2",
body: "text2"),
MyItem(
header: "header3",
body: "text3"),
];
#override
Widget build(BuildContext context) {
return _buildPage();
}
Widget _buildPage() {
return SafeArea(
top: true,
child: Scaffold(
appBar: AppBar(
title: const Text("page4"),
),
body: Center(
child: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
const Text(
'Assignments:',
style: TextStyle(fontSize: 35),
),
ExpansionPanelList(
expansionCallback: (int index, bool isExpanded) {
setState(() {
_items[index].isExpanded = !_items[index].isExpanded;
});
},
children: _items.map((MyItem item) {
return ExpansionPanel(
headerBuilder: (BuildContext context, bool isExpanded) {
return Text(item.header);
},
isExpanded: item.isExpanded,
body: Container(child: Text(item.body)));
}).toList(),
),
ElevatedButton(
child: const Text('Page 1'),
onPressed: () {
Navigator.of(this.context).push(MaterialPageRoute(
builder: (context) => const FirstPage()));
},
),
ElevatedButton(
child: const Text('Page 2'),
onPressed: () {
Navigator.of(this.context).push(MaterialPageRoute(
builder: (context) => const SecondPage()));
},
),
ElevatedButton(
child: const Text('Page 3'),
onPressed: () {
Navigator.of(this.context).push(MaterialPageRoute(
builder: (context) => const ThirdPage()));
},
),
],
),
),
));
}
}
I have thought about using onclick in combination with a function but I just can't do it If anybody could help me I would really appreciate it