Thanks to everyone answering my previous question. Decide to put the entire flutter widget program here. Using input from I got from the experts here. 

Major Issues found -

keyboardType: Flutter complains The named parameter keyboardType isn't defined.
How do I define it here?

if (inValue.length ==0) Flutter says use isempty
So I replaced like this if (inValue.isEmpty) but then Flutter shows the following
The property "isEmpty" can't be unconditionally accessed the because the receiver can be null
Try making the access conditional (using?.) or adding a null check to the target('!')

Also the onsave feature isn't working. There are others too many too list

The entire code is listed below. This code was written in a book in 2019.

import 'package:flutter/material.dart';

void main() {
runApp(const MyApp());
}

class MyApp extends StatefulWidget {
const MyApp({super.key});

@override
_MyApp createState() => _MyApp();
}



class LoginData {
String username = "";
String password = "";

}

class _MyApp extends State {

LoginData loginData = LoginData();
final GlobalKey<FormState> _formkey = GlobalKey<FormState>();

@override
Widget build(BuildContext inContext) {
return MaterialApp(home: Scaffold(
body : Container(
padding : const EdgeInsets.all(50.0),
child : Form(
key: _formkey,
child: Column(
children: [
TextFormField(
keyboardType:
TextInputType.emailAddress,
validator: (String? inValue) {
if (inValue.length ==0) {
{//do something
return "Please enter username";}
}
return null;

};
},
onsaved: (String inValue) {
loginData.username = inValue;
},
decoration: const InputDecoration(
hintText: "[email protected]",
labelText: "Username (eMail address)"
)
),
TextFormField(
obscureText: true,
validator: (String inValue)
if (inValue.length < 10) {
return "Password must be >=10 in length";
}
return null;
},
onSaved: (String inValue) {
this.loginData.password = inValue;
},
decoration: InputDecoration(
hintText : "Password"
labelText : "Password"
)
),
ElevatedButton(
child : Text("Log In!"),
onPressed: (){
if (_formkey.currentState.validate()){
_formkey.currentState.save();
print ("Username: ${_loginData.username}");
print ("Password: $_loginData.password}");
}
}
)
]
)
)
)
));
}
}

My Flutter code got the error message - No MediaQuery widget ancestor found. 

You responded back to do this - 

return MediaQuery(

    data: MediaQueryData(),

    child: MaterialApp(

    home: Scaffold(

    body: SizedBox(

    height: MediaQuery.of(context).size.height,

    child: const Dashboard(),

   ),

)

So where do I put this in my code listed below?

import 'package:flutter/material.dart';
void main() {runApp(const FoodList());}

class MyApp extends StatelessWidget {
const MyApp({super.key});

@override
Widget build(BuildContext context) {
return const MaterialApp(
home: FoodList(),
);
}
}



class FoodList extends StatelessWidget {
const FoodList({super.key});

@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text("Food List"),
),
body: ListView(
children: const <Widget>[
ListTile(
title: Text("Food Item 1"),
trailing: Checkbox(value: false, onChanged: null),
),
ListTile(
title: Text("Food Item 2"),
trailing: Checkbox(value: false, onChanged: null),
),
ListTile(
title: Text("Food Item 3"),
trailing: Checkbox(value: false, onChanged: null),
),
ListTile(
title: Text("Food Item 4"),
trailing: Checkbox(value: false, onChanged: null),
),
ListTile(
title: Text("Food Item 5"),
trailing: Checkbox(value: false, onChanged: null),
),
ElevatedButton(
onPressed: null,
child: Text('Submit'),
)
],
),
);
}
}

Using Flutter ver 3.3.6 the following flutter program  gets

No MediaQuery widget ancestor found. Someone gave me an example of this but I have no idea where to put it  my code.

return MediaQuery(

    data: MediaQueryData(),

    child: MaterialApp(

    home: Scaffold(

    body: SizedBox(

    height: MediaQuery.of(context).size.height,

    child: const Dashboard(),

   ),

)

My Original code listed below

import 'package:flutter/material.dart';
void main() {runApp(const FoodList());}

class MyApp extends StatelessWidget {
const MyApp({super.key});

@override
Widget build(BuildContext context) {
return const MaterialApp(
home: FoodList(),
);
}
}



class FoodList extends StatelessWidget {
const FoodList({super.key});

@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text("Food List"),
),
body: ListView(
children: const <Widget>[
ListTile(
title: Text("Food Item 1"),
trailing: Checkbox(value: false, onChanged: null),
),
ListTile(
title: Text("Food Item 2"),
trailing: Checkbox(value: false, onChanged: null),
),
ListTile(
title: Text("Food Item 3"),
trailing: Checkbox(value: false, onChanged: null),
),
ListTile(
title: Text("Food Item 4"),
trailing: Checkbox(value: false, onChanged: null),
),
ListTile(
title: Text("Food Item 5"),
trailing: Checkbox(value: false, onChanged: null),
),
ElevatedButton(
onPressed: null,
child: Text('Submit'),
)
],
),
);
}
}

How to resolve this error message in flutter - library_private_types_in_public_api

The line of code it's complaining is  this -

_MyPageState createState() => _MyPageState();



The flutter code lines - class MyPage extends StatefulWidget {
const MyPage({super.key});

@override
_MyPageState createState() => _MyPageState();
}