setState updating inside StatefulBuilder but not updating when using a method outside - flutter

Question

I am having a showMyModalBottomSheet that calls showModalBottomSheet which returns StatefulBuilder that has some widgets. The problem i am having is that if i setState it just works fine but if i setState in a method that i have called it does not work.
Below is my showMyModalBottomSheet method
showMyModalBottomSheet() {
showModalBottomSheet(
context: context,
shape: const RoundedRectangleBorder(
borderRadius: BorderRadius.vertical(top: Radius.circular(25))),
builder: (context) {
return StatefulBuilder(builder: (context, setState) {
return Container(
padding: EdgeInsets.only(
bottom: MediaQuery.of(context).viewInsets.bottom),
child: SingleChildScrollView(
child: Container(
width: double.infinity,
child: Column(children: [
Container(
width: double.infinity,
margin: const EdgeInsets.only(
left: 10, right: 10, top: 20, bottom: 20),
child: Text(
_titleText,
textAlign: TextAlign.center,
style:
TextStyle(fontSize: 25, fontWeight: FontWeight.bold),
),
),
Container(
width: double.infinity,
margin: const EdgeInsets.only(
left: 20, right: 20, top: 10, bottom: 10),
child: TextFormField(
key: _titleFormKey,
decoration: InputDecoration(labelText: "Enter Title"),
controller: _titleController,
validator: (title) {
if (title!.isEmpty) {
return "Please enter title";
} else {
return null;
}
},
),
),
Container(
child: ElevatedButton(
onPressed: () {
if (_titleFormKey.currentState!.validate()) {
// updating title
_titleText = _titleController.text.trim().toString();
}
},
child: Text("Update Title"),
),
)
]),
),)
);
});
});
}
When i am updating my _titleText using below way it just works fine
onPressed: () {
if (_titleFormKey.currentState!.validate()) {
_titleText = _titleController.text.trim().toString();
}
},
But when i am using my method updateTitle like below it does not update
onPressed: () {
if (_titleFormKey.currentState!.validate()) {
updateTitle(_titleController.text.trim().toString());
}
},
And below is my updateTitle method
updateTitle(String title){
setState(() {
_titleText = title;
});
}
Below is my entire code
import 'package:flutter/material.dart';
class MyPage extends StatefulWidget {
const MyPage({Key? key}) : super(key: key);
#override
State<MyPage> createState() => _MyPageState();
}
class _MyPageState extends State<MyPage> {
String _titleText = "Test Title";
final _titleFormKey = GlobalKey<FormFieldState>();
TextEditingController _titleController = TextEditingController();
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text("My Page"),
),
body: Center(
child: ElevatedButton(
onPressed: () {
showMyModalBottomSheet();
},
child: Text("Show Bottom Sheet"),
),
),
);
}
showMyModalBottomSheet() {
showModalBottomSheet(
context: context,
shape: const RoundedRectangleBorder(
borderRadius: BorderRadius.vertical(top: Radius.circular(25))),
builder: (context) {
return StatefulBuilder(builder: (context, setState) {
return Container(
padding: EdgeInsets.only(
bottom: MediaQuery.of(context).viewInsets.bottom),
child: SingleChildScrollView(
child: Container(
width: double.infinity,
child: Column(children: [
Container(
width: double.infinity,
margin: const EdgeInsets.only(
left: 10, right: 10, top: 20, bottom: 20),
child: Text(
_titleText,
textAlign: TextAlign.center,
style:
TextStyle(fontSize: 25, fontWeight: FontWeight.bold),
),
),
Container(
width: double.infinity,
margin: const EdgeInsets.only(
left: 20, right: 20, top: 10, bottom: 10),
child: TextFormField(
key: _titleFormKey,
decoration: InputDecoration(labelText: "Enter Title"),
controller: _titleController,
validator: (title) {
if (title!.isEmpty) {
return "Please enter title";
} else {
return null;
}
},
),
),
Container(
child: ElevatedButton(
onPressed: () {
if (_titleFormKey.currentState!.validate()) {
updateTitle(_titleController.text.trim().toString());
}
},
child: Text("Update Title"),
),
)
]),
),)
);
});
});
}
updateTitle(String title){
setState(() {
_titleText = title;
});
}
}
The problem is that its not updating text whenever i setState using updateTitle method.

Answer 1

updateTitle is using state class(_MyPageState) setState, that's why it is not updating. You can pass setState of StatefulBuilder while StatefulBuilder's setState is out of scope.
updateTitle(
_titleController.text.trim().toString(),
setState);
And
updateTitle(String title, setState) {
setState(() {
_titleText = title;
});
}