The getter 'length' was called on null. Receiver: null Tried calling: length - flutter

Question

I am trying to fetch device contacts in flutter using the package contacts_service and I am getting an error like this. I tried declaring the list _contact to be an empty list but that didn't worked for me. By searching on internet, I got to know that some of the fields that are fetched are null that is why it causes this error. Please help me to Solve This.
Here is my Error
import 'dart:io';
import 'package:android_intent/android_intent.dart';
import 'package:contacts_service/contacts_service.dart';
import 'package:flutter/services.dart';
import 'package:permission_handler/permission_handler.dart';
import 'package:flutter/material.dart';
import 'package:udhar/widgets/bottom_sheet.dart';
import 'dart:math';
class ContactList extends StatefulWidget {
#override
_ContactListState createState() => _ContactListState();
}
class _ContactListState extends State<ContactList> {
List<Contact> _contacts;
refreshContactsWithQuery(String query) async {
PermissionStatus permissionStatus = await _getContactPermission();
if (permissionStatus == PermissionStatus.granted) {
// Load without thumbnails initially.
var contacts = (await ContactsService.getContacts(
withThumbnails: false, query: '$query'))
.toList();
// var contacts = (await ContactsService.getContactsForPhone("8554964652"))
// .toList();
setState(() {
_contacts = contacts;
});
} else {
_handleInvalidPermissions(permissionStatus);
}
}
List colors = [
Colors.redAccent,
Colors.greenAccent,
Colors.purpleAccent,
Colors.blueAccent,
Colors.orangeAccent
];
Random random = new Random();
bool isNumeric(String s) {
if (s == null) {
return false;
}
return double.tryParse(s) != null;
}
String firstLetterWord(String str) {
String result = "";
if (isNumeric(str)) {
return "#";
}
// Traverse the string.
bool v = true;
for (int i = 0; i < str.length; i++) {
// If it is space, set v as true.
if (str[i] == ' ')
v = true;
// Else check if v is true or not.
// If true, copy character in output
// string and set v as false.
else if (str[i] != ' ' && v == true) {
result += (str[i]);
v = false;
}
}
return result;
}
#override
initState() {
super.initState();
refreshContacts();
}
refreshContacts() async {
PermissionStatus permissionStatus = await _getContactPermission();
if (permissionStatus == PermissionStatus.granted) {
// Load without thumbnails initially.
var contacts =
(await ContactsService.getContacts(withThumbnails: false)).toList();
// var contacts = (await ContactsService.getContactsForPhone("8554964652"))
// .toList();
setState(() {
_contacts = contacts;
});
} else {
_handleInvalidPermissions(permissionStatus);
}
}
updateContact() async {
Contact ninja = _contacts
.toList()
.firstWhere((contact) => contact.familyName.startsWith("Ninja"));
ninja.avatar = null;
await ContactsService.updateContact(ninja);
refreshContacts();
}
Future<PermissionStatus> _getContactPermission() async {
PermissionStatus permission = await PermissionHandler()
.checkPermissionStatus(PermissionGroup.contacts);
if (permission != PermissionStatus.granted &&
permission != PermissionStatus.disabled) {
Map<PermissionGroup, PermissionStatus> permissionStatus =
await PermissionHandler()
.requestPermissions([PermissionGroup.contacts]);
return permissionStatus[PermissionGroup.contacts] ??
PermissionStatus.unknown;
} else {
return permission;
}
}
void _handleInvalidPermissions(PermissionStatus permissionStatus) {
if (permissionStatus == PermissionStatus.denied) {
throw new PlatformException(
code: "PERMISSION_DENIED",
message: "Access to location data denied",
details: null);
} else if (permissionStatus == PermissionStatus.disabled) {
throw new PlatformException(
code: "PERMISSION_DISABLED",
message: "Location data is not available on device",
details: null);
}
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: new AppBar(
leading: IconButton(
icon: Icon(
Icons.arrow_back,
color: Colors.grey,
),
onPressed: () {
Navigator.pop(context);
}),
title: Text(
'Customer Select Karein',
style: TextStyle(color: Colors.black),
),
// Positioned(
// top: 20, child: Text('Apne customer aur supplier select karein'))
backgroundColor: Colors.white,
elevation: 0,
),
body: Column(children: <Widget>[
Expanded(
flex: 0,
child: Padding(
padding: EdgeInsets.all(10.0),
child: TextField(
decoration: inputDecoration3,
textInputAction: TextInputAction.search,
onChanged: (String s) {
refreshContactsWithQuery(s);
},
))),
Expanded(
flex: 0,
child: Padding(
padding: EdgeInsets.all(0),
child: Card(
color: Colors.white,
margin: EdgeInsets.symmetric(vertical: 10.0, horizontal: 0.0),
child: GestureDetector(
onTap: () {
openAddContacts();
},
child: ListTile(
leading: Icon(
Icons.add,
color: Colors.green,
),
title: Text(
'Manually add karein',
style: TextStyle(fontSize: 15, color: Colors.green),
),
onTap: () {
NewCustomerSheet(context);
},
),
)),
)),
Expanded(
flex: 6,
child: _contacts != null
? ListView.builder(
// separatorBuilder: (context, index) => Divider(
// color: Colors.black,
// ),
itemCount: _contacts?.length ?? 0,
itemBuilder: (BuildContext context, int index) {
Contact c = _contacts?.elementAt(index);
return Card(
elevation: 1.0,
child: ListTile(
onTap: () {
debugPrint('Name:');
debugPrint(c.displayName ?? "");
print(c.phones.first.value);
},
leading: CircleAvatar(
child: Text(
firstLetterWord(c.displayName).toUpperCase(),
style: TextStyle(color: Colors.white),
),
backgroundColor:
colors[random.nextInt(colors.length)],
),
title: Container(
child: Row(
children: <Widget>[
Flexible(
child: Text(c.displayName ?? "",
overflow: TextOverflow.ellipsis,
style: TextStyle(fontSize: 15.0)),
),
],
)),
trailing: Text(
'₹ 500',
style: TextStyle(
fontSize: 20.0,
color: Colors.blue,
),
),
//Divider(height:50,);
),
);
},
)
: Center(
child: CircularProgressIndicator(),
),
)
]),
);
}
void openAddContacts() async {
if (Platform.isAndroid) {
final AndroidIntent intent = AndroidIntent(
action: 'ContactsContract.Intents.Insert.ACTION',
category: 'ContactsContract.RawContacts.CONTENT_TYPE',
);
await intent.launch();
}
}
InputDecoration inputDecoration3 = InputDecoration(
hintText: 'Search',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10),
),
fillColor: Colors.grey[200],
filled: true,
prefixIcon: Icon(
Icons.search,
color: Colors.grey,
),
);enter code here
}