Thanks to everyone for there help on my previous question.

Using Flutter ver 3.3.8 and Android Studio Dolphin | 2021.3.1 Patch 1 (This is the latest version that i'm using. Since the book is using an older version.)

Modified the Widget with this code see below

Still having issues with this line of code -

if (inValue?.isEmpty) {
return "Please enter username";
}

Flutter shows this msg - A nullable expression can't be used as a condition. Try checking that the value isn't 'null' before using it as a condition. See screenshot of the message listed below. A;so put the full code below the screenshot.

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?.isEmpty) {
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();
}