How to solve "a build function has returned null" in flutter app? - flutter

Question

App was working perfectly before and then I had to make some changes to allow or restrict calling feature in the app based on subscription level of the user, by passing the variable value from one screen to another using provider.
one Screen 1 i am using :
Future<void> _verifyPuchase(String id) async {
PurchaseDetails purchase = _hasPurchased(id);
if (purchase != null && purchase.status == PurchaseStatus.purchased) {
print(purchase.productID);
if (Platform.isIOS) {
await _iap.completePurchase(purchase);
print('Achats antérieurs........$purchase');
isPuchased = true;
}
isPuchased = true;
checkIsPurchsed(isPurchsed: isPuchased);
} else {
isPuchased = false;
checkIsPurchsed(isPurchsed: isPuchased);
}
}
and have i have a class on screen 1:
class checkIsPurchsed with ChangeNotifier{
bool isPurchsed;
checkIsPurchsed({this.isPurchsed});
notifyListeners();
}
and on screen 5 I have:
Consumer<checkIsPurchsed>(
builder: (context,isPurchsed,child){
return isPurchsed.isPurchsed ? IconButton(
icon: Icon(Icons.call), onPressed: () => onJoin("AudioCall"),
):Center(child: Text(
'Sorry you have not subscribe the package',
),);
},
),
Consumer<checkIsPurchsed>(
builder: (context,isPurchsed,child){
return isPurchsed.isPurchsed ? IconButton(
icon: Icon(Icons.video_call), onPressed: () => onJoin("VideoCall"),
):Center(child: Text(
'Sorry you have not subscribe the package',
),);
},
),
on screen 5 when i try to open a chat this is what i am getting :
the icon buttons on which i am checking the purchase status appear when chat is opened , but after adding the above mentioned modifications the chat itself isnt opening and instead i am getting the red screen.
Update 1:
class ChatPage extends StatefulWidget {
final User sender;
final String chatId;
final User second;
ChatPage({this.sender, this.chatId, this.second});
#override
_ChatPageState createState() => _ChatPageState();
}
class _ChatPageState extends State<ChatPage> {
bool isBlocked = false;
final db = Firestore.instance;
CollectionReference chatReference;
final TextEditingController _textController = new TextEditingController();
bool _isWritting = false;
final _scaffoldKey = GlobalKey<ScaffoldState>();
//Ads _ads = new Ads();
#override
void initState() {
//_ads.myInterstitial()
//..load()
//..show();
print("object -${widget.chatId}");
super.initState();
chatReference =
db.collection("chats").document(widget.chatId).collection('messages');
checkblock();
}
var blockedBy;
checkblock() {
chatReference.document('blocked').snapshots().listen((onData) {
if (onData.data != null) {
blockedBy = onData.data['blockedBy'];
if (onData.data['isBlocked']) {
isBlocked = true;
} else {
isBlocked = false;
}
if (mounted) setState(() {});
}
// print(onData.data['blockedBy']);
});
}
List<Widget> generateSenderLayout(DocumentSnapshot documentSnapshot) {
return <Widget>[
Expanded(
child: Column(
crossAxisAlignment: CrossAxisAlignment.end,
children: <Widget>[
Container(
child: documentSnapshot.data['image_url'] != ''
? InkWell(
child: Column(
crossAxisAlignment: CrossAxisAlignment.end,
children: <Widget>[
new Container(
margin: EdgeInsets.only(
top: 2.0, bottom: 2.0, right: 15),
child: Stack(
children: <Widget>[
CachedNetworkImage(
placeholder: (context, url) => Center(
child: CupertinoActivityIndicator(
radius: 10,
),
),
errorWidget: (context, url, error) =>
Icon(Icons.error),
height:
MediaQuery.of(context).size.height * .65,
width: MediaQuery.of(context).size.width * .9,
imageUrl:
documentSnapshot.data['image_url'] ?? '',
fit: BoxFit.fitWidth,
),
Container(
alignment: Alignment.bottomRight,
child:
documentSnapshot.data['isRead'] == false
? Icon(
Icons.done,
color: secondryColor,
size: 15,
)
: Icon(
Icons.done_all,
color: primaryColor,
size: 15,
),
)
],
),
height: 150,
width: 150.0,
color: secondryColor.withOpacity(.5),
padding: EdgeInsets.all(5),
),
Padding(
padding: const EdgeInsets.only(right: 10),
child: Text(
documentSnapshot.data["time"] != null
? DateFormat.yMMMd()
.add_jm()
.format(documentSnapshot.data["time"]
.toDate())
.toString()
: "",
style: TextStyle(
color: secondryColor,
fontSize: 13.0,
fontWeight: FontWeight.w600,
)),
)
],
),
onTap: () {
Navigator.of(context).push(
CupertinoPageRoute(
builder: (context) => LargeImage(
documentSnapshot.data['image_url'],
),
),
);
},
)
: Container(
padding: EdgeInsets.symmetric(
horizontal: 15.0, vertical: 10.0),
width: MediaQuery.of(context).size.width * 0.65,
margin: EdgeInsets.only(
top: 8.0, bottom: 8.0, left: 80.0, right: 10),
decoration: BoxDecoration(
color: primaryColor.withOpacity(.1),
borderRadius: BorderRadius.circular(20)),
child: Column(
children: <Widget>[
Row(
crossAxisAlignment: CrossAxisAlignment.end,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Expanded(
child: Container(
child: Text(
documentSnapshot.data['text'],
style: TextStyle(
color: Colors.black87,
fontSize: 16.0,
fontWeight: FontWeight.w600,
),
),
),
),
Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
Text(
documentSnapshot.data["time"] != null
? DateFormat.MMMd()
.add_jm()
.format(documentSnapshot
.data["time"]
.toDate())
.toString()
: "",
style: TextStyle(
color: secondryColor,
fontSize: 13.0,
fontWeight: FontWeight.w600,
),
),
SizedBox(
width: 5,
),
documentSnapshot.data['isRead'] == false
? Icon(
Icons.done,
color: secondryColor,
size: 15,
)
: Icon(
Icons.done_all,
color: primaryColor,
size: 15,
)
],
),
],
),
],
)),
),
],
),
),
];
}
_messagesIsRead(documentSnapshot) {
return <Widget>[
Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
InkWell(
child: CircleAvatar(
backgroundColor: secondryColor,
radius: 25.0,
child: ClipRRect(
borderRadius: BorderRadius.circular(90),
child: CachedNetworkImage(
imageUrl: widget.second.imageUrl[0] ?? '',
useOldImageOnUrlChange: true,
placeholder: (context, url) => CupertinoActivityIndicator(
radius: 15,
),
errorWidget: (context, url, error) => Icon(Icons.error),
),
),
),
onTap: () => showDialog(
barrierDismissible: false,
context: context,
builder: (context) {
return Info(widget.second, widget.sender, null);
}),
),
],
),
Expanded(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Container(
child: documentSnapshot.data['image_url'] != ''
? InkWell(
child: Column(
crossAxisAlignment: CrossAxisAlignment.end,
children: <Widget>[
new Container(
margin: EdgeInsets.only(
top: 2.0, bottom: 2.0, right: 15),
child: CachedNetworkImage(
placeholder: (context, url) => Center(
child: CupertinoActivityIndicator(
radius: 10,
),
),
errorWidget: (context, url, error) =>
Icon(Icons.error),
height: MediaQuery.of(context).size.height * .65,
width: MediaQuery.of(context).size.width * .9,
imageUrl:
documentSnapshot.data['image_url'] ?? '',
fit: BoxFit.fitWidth,
),
height: 150,
width: 150.0,
color: Color.fromRGBO(0, 0, 0, 0.2),
padding: EdgeInsets.all(5),
),
Padding(
padding: const EdgeInsets.only(right: 10),
child: Text(
documentSnapshot.data["time"] != null
? DateFormat.yMMMd()
.add_jm()
.format(documentSnapshot.data["time"]
.toDate())
.toString()
: "",
style: TextStyle(
color: secondryColor,
fontSize: 13.0,
fontWeight: FontWeight.w600,
)),
)
],
),
onTap: () {
Navigator.of(context).push(CupertinoPageRoute(
builder: (context) => LargeImage(
documentSnapshot.data['image_url'],
),
));
},
)
: Container(
padding: EdgeInsets.symmetric(
horizontal: 15.0, vertical: 10.0),
width: MediaQuery.of(context).size.width * 0.65,
margin: EdgeInsets.only(top: 8.0, bottom: 8.0, right: 10),
decoration: BoxDecoration(
color: secondryColor.withOpacity(.3),
borderRadius: BorderRadius.circular(20)),
child: Column(
children: <Widget>[
Row(
crossAxisAlignment: CrossAxisAlignment.end,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Expanded(
child: Container(
child: Text(
documentSnapshot.data['text'],
style: TextStyle(
color: Colors.black87,
fontSize: 16.0,
fontWeight: FontWeight.w600,
),
),
),
),
Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
Text(
documentSnapshot.data["time"] != null
? DateFormat.MMMd()
.add_jm()
.format(documentSnapshot
.data["time"]
.toDate())
.toString()
: "",
style: TextStyle(
color: secondryColor,
fontSize: 13.0,
fontWeight: FontWeight.w600,
),
),
],
),
],
),
],
)),
),
],
),
),
];
}
List<Widget> generateReceiverLayout(DocumentSnapshot documentSnapshot) {
if (!documentSnapshot.data['isRead']) {
chatReference.document(documentSnapshot.documentID).updateData({
'isRead': true,
});
return _messagesIsRead(documentSnapshot);
}
return _messagesIsRead(documentSnapshot);
}
generateMessages(AsyncSnapshot<QuerySnapshot> snapshot) {
return snapshot.data.documents
.map<Widget>((doc) => Container(
margin: const EdgeInsets.symmetric(vertical: 10.0),
child: new Row(
mainAxisAlignment: MainAxisAlignment.center,
children: doc.data['type'] == "Call"
? [
Text(doc.data["time"] != null
? "${doc.data['text']} : " +
DateFormat.yMMMd()
.add_jm()
.format(doc.data["time"].toDate())
.toString() +
" by ${doc.data['sender_id'] == widget.sender.id ? "You" : "${widget.second.name}"}"
: "")
]
: doc.data['sender_id'] != widget.sender.id
? generateReceiverLayout(
doc,
)
: generateSenderLayout(doc)),
))
.toList();
}
#override
Widget build(BuildContext context) {
ChangeNotifierProvider<checkIsPurchsed>(
create: (context)=>checkblock(),
child: Scaffold(
key: _scaffoldKey,
backgroundColor: Colors.white,
appBar: AppBar(
centerTitle: true,
elevation: 0,
title: Text(widget.second.name),
leading: IconButton(
icon: Icon(Icons.arrow_back_ios),
color: Colors.white,
onPressed: () => Navigator.pop(context),
),
actions: <Widget>[
Consumer<checkIsPurchsed>(
builder: (context,isPurchsed,child){
return isPurchsed.isPurchsed ? IconButton(
icon: Icon(Icons.call), onPressed: () => onJoin("AudioCall"),
):Center(child: Text(
'Sorry you have not subscribe the package',
),);
},
),
Consumer<checkIsPurchsed>(
builder: (context,isPurchsed,child){
return isPurchsed.isPurchsed ? IconButton(
icon: Icon(Icons.video_call), onPressed: () => onJoin("VideoCall"),
):Center(child: Text(
'Sorry you have not subscribe the package',
),);
},
),
}

Answer 1

The problematic area is:
#override
Widget build(BuildContext context) {
ChangeNotifierProvider<checkIsPurchsed>(
There's no return in front of ChangeNotifierProvider, so it doesn't return a Widget. Correct would be:
#override
Widget build(BuildContext context) {
return ChangeNotifierProvider<checkIsPurchsed>(