stream subscription throwing an error in dart in flutter app? - dart

Question

I am using the connectivity plugin in my flutter to check for the connection status, but occasionally hitting the error PlatForm Exception(No active stream to cancel, null) even though i have handled the null case. I have subscribed to the stream in initState and cancelled the subscription in dispose state
my code looks something like this.
StreamSubscription streamConnectionStatus;
------------
//remaining code
------------
#override
void initState() {
getConnectionStatus();
}
getConnectionStatus() async {
streamConnectionStatus = new Connectivity()
.onConnectivityChanged
.listen((ConnectivityResult result) {
// Got a new connectivity status!
if (result == ConnectivityResult.mobile ||
result == ConnectivityResult.wifi) {
setState(() {
boolHasConnection = true;
});
} else {
setState(() {
boolHasConnection = false;
});
}
});
#override
void dispose() {
try {
streamConnectionStatus?.cancel();
} catch (exception, stackTrace) {
print(exception.toString());
updateError(exception.toString(), stackTrace);
} finally {
super.dispose();
}
}
this is actually driving me crazy but i am guessing i am missing something or do i have to change the code.
Many thanks,
Mahi

Answer 1

I encountered a similar issue. This is what helped me.
I had subscribed the stream exposed by connectivity plugin in different widgets in the same widget tree. I removed the subscription from child widgets and retained the subscription only in the parent and passed on the connection status to the children from parent.
By doing so my code got more cleaner and the stream subscription was maintained / disposed only at one place. Then I didn't encounter this issue any more.

Answer 2

I think your dispose function is defined inside getConnectionStatus. The IDE might not throw error as it still is a valid definition. Just remove it from inside and make sure it lies in the respective class. Your code just works like a charm.
Example:
class ConnectivityExample extends StatefulWidget {
#override
_ConnectivityExampleState createState() => new _ConnectivityExampleState();
}
class _ConnectivityExampleState extends State<ConnectivityExample> {
StreamSubscription streamConnectionStatus;
bool boolHasConnection;
#override
void initState() {
getConnectionStatus();
}
Future<Null> getConnectionStatus() async {
streamConnectionStatus = new Connectivity()
.onConnectivityChanged
.listen((ConnectivityResult result) {
debugPrint(result.toString());
if (result == ConnectivityResult.mobile ||
result == ConnectivityResult.wifi) {
setState(() {
boolHasConnection = true;
});
} else {
setState(() {
boolHasConnection = false;
});
}
});
}
// dispose function inside class
#override
void dispose() {
try {
streamConnectionStatus?.cancel();
} catch (exception, stackTrace) {
print(exception.toString());
} finally {
super.dispose();
}
}
#override
Widget build(BuildContext context) {
return new Container(
color: Colors.white,
alignment: Alignment.center,
child: new Text(boolHasConnection.toString()),
);
}
}
Hope that helps!