Flutter SteamBuilder snapshot.data is null - flutter

Question

I am new to flutter. I am trying to use SteamBuilder to retrieve snapshot data.
But snapshot.data is returning null.
snapshot.connectionState == ConnectionState.done
is false.
snapshot.hasData
is false.
This is the dart file in which I am trying to retrieve snapshot data
return StreamBuilder<UserData>(
stream: DatabaseService(uid: user.uid).userData,
builder: (context, snapshot) {
//print(snapshot.connectionState == ConnectionState.done);
//print(snapshot.data);
if(snapshot.hasData){
print('snapshot has data');
UserData userData = snapshot.data;
return Form(
key: _formKey,
child: Column(
children: <Widget>[
Text(
'Update your brew settings.',
style: TextStyle(fontSize: 18.0),
),
SizedBox(height: 20.0),
TextFormField(
initialValue: userData.name,
decoration: textInputDecorator,
validator: (val) => val.isEmpty ? 'Please enter a name' : null,
onChanged: (val) => setState(() => _currentName = val),
),
SizedBox(height: 10.0),
DropdownButtonFormField(
value: _currentSugars ?? userData.sugars,
decoration: textInputDecorator,
items: sugars.map((sugar) {
return DropdownMenuItem(
value: sugar,
child: Text('$sugar sugars'),
);
}).toList(),
onChanged: (val) => setState(() => _currentSugars = val ),
),
SizedBox(height: 10.0),
Slider(
value: _currentStrength.toDouble() ?? userData.strength,
activeColor: Colors.brown[_currentStrength ?? userData.strength],
inactiveColor: Colors.brown[_currentStrength ?? userData.strength],
min: 100.0,
max: 900.0,
divisions: 8,
onChanged: (val) => setState(() => _currentStrength = val.round()),
),
RaisedButton(
color: Colors.pink[400],
child: Text(
'Update',
style: TextStyle(color: Colors.white),
),
onPressed: () async {
print(_currentName);
print(_currentSugars);
print(_currentStrength);
}
),
],
),
);
} else {
print('snapshot doesnt have data');
return Loading();
}
}
);
This is the stream
Stream<UserData> get userData {
return brewCollection.document(uid).snapshots().map(_userDataFromSnapshot);
}
brewCollection-
final CollectionReference brewCollection = Firestore.instance.collection('brews');
_userDataFromSnapshot
UserData _userDataFromSnapshot(DocumentSnapshot snapshot) {
return UserData(
uid: uid,
name: snapshot.data['name'],
sugars: snapshot.data['sugars'],
strength: snapshot.data['strength']
);
}
UserData
class UserData {
final String uid;
final String name;
final String strength;
final int sugars;
UserData({ this.uid, this.sugars, this.strength, this.name });
}
Since I am new to Flutter I don't know how to approach this issue.
Please help me out. Thank you.

Answer 1

Normally you need to check 3 cases:
snapshot is null (before any stream or action is fired, usually right
when the Widget is created)
snapshot is not null and data is null/invalid (stream is registered but no data is emitted yet)
snapshot is not null and data is valid (received data)

Answer 2

The UserData class should have been
class UserData {
final String uid;
final String name;
final int strength; // type int not String
final String sugars; // type String not int
UserData({ this.uid, this.sugars, this.strength, this.name });
}
I got confused with datatypes of strength and sugars. My bad.
It was a stupid mistake.
Thank you for responding :)

Answer 3

Here you have not handle error so it will be difficult to know what happens by just seeing code so also catch error on snapshot as
if(snapshot.hasData){
//Show widget with data
}else if(snapshot.hasError){
return Center(
child:Text(snapshot.error.toString());
);
}else{
return CircularProgressIndicator();
}