The method '[ ]' was called on null - firebase

Question

I am running my app and getting the error:
"NoSuchMethodError: The Method '[ ]' was called on null. Receiver: null. Tried calling: ."
This is also happening for "photourl" and "total questions", all three fields that I have in my firestore database.
This error is occurring after I implemented provider, so I am not sure if this is a result of this.
My code is below:
void main() {
runApp(
ChangeNotifierProvider(
builder: (context) => UserModel(),
child: MyApp(),
),
);
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Profile Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Profile'),
);
}
}
class User {
final int name;
final DocumentReference reference;
User.fromMap(Map<String, dynamic> map, {this.reference})
: name = map['name'];
User.fromSnapshot(DocumentSnapshot snapshot)
: this.fromMap(snapshot.data, reference: snapshot.reference);
}
class Photo {
final int photourl;
final DocumentReference reference;
Photo.fromMap(Map<String, dynamic> map, {this.reference})
: photourl = map['photourl'];
Photo.fromSnapshot(DocumentSnapshot snapshot)
: this.fromMap(snapshot.data, reference: snapshot.reference);
}
class Questions {
final int totalquestions;
final DocumentReference reference;
Questions.fromMap(Map<String, dynamic> map, {this.reference})
: totalquestions = map['totalquestions'];
Questions.fromSnapshot(DocumentSnapshot snapshot)
: this.fromMap(snapshot.data, reference: snapshot.reference);
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
#override
Widget build(BuildContext context) {
final _width = MediaQuery.of(context).size.width;
final _height = MediaQuery.of(context).size.height;
return Consumer<UserModel>(builder: (context, userModel, child) {
return StreamBuilder<DocumentSnapshot>(
stream: Firestore.instance.collection(userModel.uid)
.document(userModel.uid).snapshots(),
builder: (context, snapshot) {
if (snapshot.hasData) {
return Stack(
children: <Widget>[
new Container(
color: Colors.blue,
),
new Image.network(
snapshot.data['photourl'].toString(),
fit: BoxFit.fill,
),
new BackdropFilter(
filter: new ui.ImageFilter.blur(
sigmaX: 6.0,
sigmaY: 6.0,
),
child: new Container(
decoration: BoxDecoration(
color: Colors.blue.withOpacity(0.9),
borderRadius: BorderRadius.all(Radius.circular(50.0)),
),
)),
new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
centerTitle: false,
elevation: 0.0,
backgroundColor: Colors.transparent,
),
drawer: new Drawer(
child: new Container(),
),
backgroundColor: Colors.transparent,
body: new Center(
child: new Column(
children: <Widget>[
new SizedBox(
height: _height / 12,
),
new CircleAvatar(
radius: _width < _height ? _width / 4 : _height / 4,
backgroundImage: NetworkImage(snapshot.data['photourl']),
),
new SizedBox(
height: _height / 25.0,
),
new Text(
snapshot.data['name'],
style: new TextStyle(fontWeight: FontWeight.bold, fontSize: _width / 15, color: Colors.white),
),
new Padding(
padding: new EdgeInsets.only(top: _height / 30, left: _width / 8, right: _width / 8),
),
new Divider(
height: _height / 15,
color: Colors.white,
),
new Row(
children: <Widget>[
rowCell(snapshot.data['totalquestions'], 'Answers'),
rowCell('£ ${int.parse(snapshot.data['totalquestions']) * 2}', 'Earned'),
],
),
new Divider(height: _height / 15, color: Colors.white),
],
),
),
),
],
);
} else {
return CircularProgressIndicator();
}
},
);
});
}

Answer 1

The error simply states that the operator [] is called on a variable that does not contain a Map object and is rather null. I would suggest you to place a check for null or provide a default value for map using ?? everytime before you access a property of map.

Answer 2

This is just speculation but I think you made a mistake when specifying your stream. The collection you query is userModel.uid. Is that how your collection is named?

Answer 3

You should always check if the image is null when you work with NetworkImage since its an async task. The code could look like this:
backgroundImage: snapshot.data['photourl'] != null ?NetworkImage(snapshot.data['photourl']) : Container(),