How to show different Widget when user is offline while using StreamBuilder? - dart

Question

I am trying to fetch some data from the internet. With the use of FutureBuilder, handling for various cases like offline, online,error is quite easy but I am using StreamBuilder and I am not able to understand how to handle offline case
Following is my code to use StreamBuilder which works but I have not handled offline data or error
return StreamBuilder(
builder: (context, AsyncSnapshot<SchoolListModel> snapshot) {
if (snapshot.hasError) {
return Expanded(
child: Center(
child: Text(SOMETHING_WENT_WRONG),
));
}
if (!snapshot.hasData) {
return Expanded(
child: Center(
child: CircularProgressIndicator(),
),
);
}
if (snapshot.data != null) {
if (snapshot.data.status == 1) {
return buildSchoolList(snapshot.data.schoolListData);
} else {
showMessageDialog(snapshot.data.msg.toString(), context);
}
}
},
stream: schoolListBloc.schoolList,
);
}
Now to handle the offline case I am doing the following two options which don't work in my case
Option one.
return StreamBuilder(
builder: (context, AsyncSnapshot<SchoolListModel> snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.none:
return Text(SOMETHING_WENT_WRONG);
case ConnectionState.active:
case ConnectionState.waiting:
return Expanded(
child: Center(
child: CircularProgressIndicator(),
),
);
case ConnectionState.done:
if (snapshot.hasError) {
return errorData(snapshot);
} else {
if (snapshot.data.status == 1) {
return buildSchoolList(snapshot.data.schoolListData);
} else {
showMessageDialog(snapshot.data.msg.toString(), context);
}
}
}
},
stream: schoolListBloc.schoolList,
);
}
I keep seeing the CircularProgressIndicator and no error on the console.
I fail to understand why the above switch case works for FuturBuilder and not StreamBuilder.
Second Option.
Future<bool> checkInternetConnection() async {
try {
final result = await InternetAddress.lookup('google.com');
if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
print('connected');
return true;
}
} on SocketException catch (_) {
print('not connected');
return false;
}
return false;
}
return StreamBuilder(
builder: (context, AsyncSnapshot<SchoolListModel> snapshot) {
checkInternetConnection().then((isAvailable) {
if (isAvailable) {
if (!snapshot.hasData || snapshot.data == null) {
return Center(
child: CircularProgressIndicator(),
);
}
if (snapshot.data != null) {
if (snapshot.data.status == 1) {
return buildSchoolList(snapshot.data.schoolListData);
} else {
showMessageDialog(snapshot.data.msg.toString(), context);
}
}
} else {
return Center(
child: Column(
children: <Widget>[
Text(CHECK_YOUR_INTERNET_CONNECTION),
RaisedButton(
onPressed: () {},
child: Text(TRY_AGAIN),
)
],
),
);
}
}); },
stream: schoolListBloc.schoolList,
);
}
Using this option throws the following error
the following assertion was thrown building StreamBuilder<SchoolListModel>(dirty, state:
I/flutter ( 5448): _StreamBuilderBaseState<SchoolListModel, AsyncSnapshot<SchoolListModel>>#dd970):
I/flutter ( 5448): A build function returned null.
I/flutter ( 5448): The offending widget is: StreamBuilder<SchoolListModel>
I/flutter ( 5448): Build functions must never return null. To return an empty space that causes the building widget to
I/flutter ( 5448): fill available room, return "new Container()". To return an empty space that takes as little room as..
What approach should I take with the following cases of offline, online and error data when using StreamBuilder

Answer 1

You can add Error to Stream and catch it in StreamBuilder like this:
_someStreamCtrl.addError(error); // Client is offline
And in StreamBuilder:
StreamBuilder<String>(
stream: someStream,
initialData: [],
builder: (BuildContext context,
AsyncSnapshot<String> snap) {
if (snap.hasError)
return ErrorWidget(); //Error
if (snap.hasData)
return // Desired widget
//if waiting
return CircularProgressIndicator();
);
},
);