The method 'getUsers' was called on null. Receiver: null Tried calling: getUsers() - flutter

Question

I am getting error on red screen right after i run my app. My first screen is login screen. I want to simply register the user and login the user. but when i use the getUsers() or getLogin() I get the above error. I am fed up of this error. Searched everywhere but m not able to find any working solutions. Please can u please write the code which i need to add. Please help me.
UserLogin.dart
import 'dart:ui';
import 'package:customer/models/registerUser.dart';
import 'package:customer/screens/UserRegistration.dart';
import 'package:customer/screens/people_list.dart';
import 'package:customer/services/db_service.dart';
import 'package:customer/utils/form_helper.dart';
import 'package:flutter/material.dart';
import 'ForgotPassword.dart';
class UserLogin extends StatefulWidget {
#override
State<StatefulWidget> createState() {
return UserLoginState();
}
}
class UserLoginState extends State<UserLogin>{
final reguser = RegisterUser();
String name,_password,_email;
var _formKey=GlobalKey<FormState>();
RegisterUser model;
DBService dbService;
var _minimumPadding = 5.0;
TextEditingController usernameController=TextEditingController();
TextEditingController passwordController=TextEditingController();
bool isHiddenPassword=true;
final scaffoldKey = new GlobalKey<ScaffoldState>();
void _showSnackBar(String text) {
scaffoldKey.currentState.showSnackBar(new SnackBar(
content: new Text(text),
));
}
void _togglePasswordView() {
setState(() {
isHiddenPassword = !isHiddenPassword;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.white,
appBar: AppBar(
title: Text('Customer Tracking System'),),
body:_fetchData(),
);
}
Widget _fetchData(){
return FutureBuilder<List<RegisterUser>>(
future: dbService.getUsers(),
builder:
(BuildContext context, AsyncSnapshot<List<RegisterUser>> userDetails) {
if (userDetails.hasData) {
return _loginUI(userDetails.data);
}
return CircularProgressIndicator();
},
);
}
Widget _loginUI(List<RegisterUser> userDetails){
TextStyle textStyle = Theme.of(context).textTheme.title;
var height = MediaQuery.of(context).size.height;
var width = MediaQuery.of(context).size.width;
Form(
key: _formKey,
child: Container(
child: Padding(
padding: EdgeInsets.all(_minimumPadding * 2),
child: ListView
(
children: <Widget>[
Text("Login".toUpperCase(),
style: TextStyle(
fontSize: 40.0, fontWeight: FontWeight.bold),
textAlign: TextAlign.center),
SizedBox(height: height * 0.08,),
Divider(),
Padding(
padding: EdgeInsets.only(
top: _minimumPadding * 3,
bottom: _minimumPadding),
child: TextFormField(
controller: usernameController,
style: textStyle,
validator: (String value) {
if (value.isEmpty) {
return 'Please Enter Name';
}
return null;
},
onSaved: (String value) {
_email = value;
},
decoration: InputDecoration(
// filled: true,
//fillColor: Colors.white,
prefixIcon: Icon(Icons.person),
labelText: 'Username',
hintText: 'Username',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(25.0)
)
)
)),
Padding(
padding: EdgeInsets.only(
top: _minimumPadding * 3,
bottom: _minimumPadding),
child: TextFormField(
style: textStyle,
obscureText: isHiddenPassword,
controller: passwordController,
validator: (String value) {
if (value.isEmpty) {
return 'Please Enter Name';
}
return null;
},
onSaved: (String value) {
_password = value;
},
decoration: InputDecoration(
prefixIcon: Icon(Icons.lock),
suffixIcon: InkWell(
onTap: _togglePasswordView,
child: Icon(Icons.visibility)),
labelText: 'Password',
hintText: 'Password',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(25.0)
)
)
)
),
InkWell(
onTap: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => ForgotPassword()));
},
child: Text(
"Forgot Password ?",
style: TextStyle(
fontSize: 18,
color: Colors.purpleAccent,
//fontWeight: FontWeight.bold,
letterSpacing: 1.7),
textAlign: TextAlign.right,
),
),
SizedBox(
height: height * 0.08,
),
GestureDetector(
onTap: () {
_submit();
},
child: Container(
padding:
EdgeInsets.symmetric(horizontal: 26, vertical: 20),
decoration: BoxDecoration(
//gradient: new LinearGradient(
//colors: [Colors.purple, Colors.purpleAccent]),
color: Theme.of(context).primaryColor,
borderRadius: BorderRadius.circular(20),
boxShadow: [
BoxShadow(
blurRadius: 4,
//color: Colors.purpleAccent,
offset: Offset(2, 2))
]),
child: Text(
"Login".toUpperCase(),
style: TextStyle(
fontSize: 20,
color: Colors.white,
fontWeight: FontWeight.bold,
letterSpacing: 1.7),
textAlign: TextAlign.center,
),
),
),
SizedBox(
height: height * 0.05,
),
SizedBox(
height: height * 0.05,
),
Row(
children: <Widget>[
Expanded(
child: Text("Not yet registered?",
style: TextStyle(
fontSize: 25.0)
)
),
GestureDetector(
onTap: () {
Navigator.push(context,
MaterialPageRoute(builder: (context) => UserRegistration()));
},
child: Center(
child: Container(
padding:
EdgeInsets.symmetric(
horizontal: 26, vertical: 10),
decoration: BoxDecoration(
//gradient: new LinearGradient(
// colors: [Colors.purple, Colors.purpleAccent]),
color: Theme.of(context).primaryColor,
borderRadius: BorderRadius.circular(20),
boxShadow: [
BoxShadow(
blurRadius: 4,
//color:,
offset: Offset(2, 2))
]),
child: Text(
"Register".toUpperCase(),
style: TextStyle(
fontSize: 20,
color: Colors.white,
fontWeight: FontWeight.bold,
letterSpacing: 1.7),
textAlign: TextAlign.center,
),
),
),
)
],
),
],
)),
),
);
}
bool validateAndSave() {
final form = _formKey.currentState;
if (form.validate()) {
form.save();
return true;
}
return false;
}
void _submit(){
final form = _formKey.currentState;
var res;
if (validateAndSave()) {
setState(() {
//getLogin(_email, _password);
res=dbService.getLogin(_email, _password).then((value) {
if(res!=0){
FormHelper.showMessage(
context,
"Login",
"Login Successfull",
"Ok",
() {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => People_List(),
),
);
},
);}
else {
FormHelper.showMessage(
context,
"Login",
"Login not Successfull",
"Ok", () {}
);
}
});
});
}
}
}
RegisterUser.dart
import 'model.dart';
class RegisterUser extends Model {
static String table = 'userDetails';
int id;
String firstName;
String lastName;
String mobileNum;
String emailId;
String address;
String userType;
String password;
RegisterUser({
this.id,
this.firstName,
this.lastName,
this.mobileNum,
this.emailId,
this.address,
this.userType,
this.password
});
static RegisterUser fromMap(Map<String, dynamic> map) {
return RegisterUser(
id: map["id"],
firstName: map['firstName'].toString(),
lastName: map['lastName'],
mobileNum: map['mobileNum'],
emailId: map['emailId'],
address: map['address'],
userType: map['userType'],
password: map['password']
);
}
Map<String, dynamic> toMap() {
Map<String, dynamic> map = {
'id': id,
'firstName': firstName,
'lastName': lastName,
'mobileNum': mobileNum,
'emailId': emailId,
'address': address,
'userType':userType,
'password':password
};
if (id != null) {
map['id'] = id;
}
return map;
}
}
db_service.dart
import 'package:customer/models/registerUser.dart';
import 'package:customer/utils/database_helper.dart';
Future<List<RegisterUser>> getUsers() async {
await DB.init();
List<Map<String, dynamic>> userDetails = await DB.query(RegisterUser.table);
return userDetails.map((item) => RegisterUser.fromMap(item)).toList();
}
Future<List<RegisterUser>> getLogin(String email, String password) async {
await DB.init();
List<Map<String, dynamic>> res = await DB.rawQuery("SELECT * FROM userDetails WHERE emailId = '$email' and password = '$password'");
if (res.length > 0) {
return res.map((item) => RegisterUser.fromMap(item)).toList();
//return new User.fromMap(res.first);
}
return null;
}

Answer 1

You need a line with dbService = something before you can do dbService.getUsers() because just saying DbService dbService; initializes it to be null.
It's like a paper with no phone number on it and you are trying to call someone with it. You need to write down a phone number on it.

Answer 2

I finally got the answer to my question.
I had to just instantiate the DBService.
i.e DBService dbService=new DBService();
class UserLoginState extends State<UserLogin>{
final reguser = RegisterUser();
String name,_password,_email;
var _formKey=GlobalKey<FormState>();
RegisterUser model;
DBService dbService=new DBService();
...