Location and GPS in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output of this Flutter widget showing GPS coordinates?

Consider this Flutter widget that tries to display the current latitude and longitude after fetching location. What will be shown on the screen after the location is fetched successfully?

Flutter

class LocationWidget extends StatefulWidget {
  @override
  State<LocationWidget> createState() => _LocationWidgetState();
}

class _LocationWidgetState extends State<LocationWidget> {
  double? latitude;
  double? longitude;

  @override
  void initState() {
    super.initState();
    fetchLocation();
  }

  Future<void> fetchLocation() async {
    await Future.delayed(Duration(seconds: 1));
    setState(() {
      latitude = 37.4219983;
      longitude = -122.084;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: latitude == null || longitude == null
            ? Text('Loading location...')
            : Text('Lat: $latitude, Lon: $longitude'),
      ),
    );
  }
}

A Text widget showing 'Lat: 0.0, Lon: 0.0' after 1 second

B Text widget showing 'Loading location...' initially, then 'Lat: 37.4219983, Lon: -122.084' after 1 second

C Text widget showing 'Lat: null, Lon: null' immediately and never updates

D App crashes due to null error when accessing latitude and longitude

💡 Hint

Think about how setState updates the UI after async data is fetched.

The widget starts with latitude and longitude as null, so it shows 'Loading location...'. After 1 second, fetchLocation sets the values and calls setState, which rebuilds the widget to show the actual coordinates.

🧠 Conceptual

intermediate

Which permission is required to access GPS location on Android in Flutter?

To get the user's current GPS location in a Flutter app running on Android, which permission must be declared in the AndroidManifest.xml file?

A <uses-permission android:name="android.permission.INTERNET" />

B <uses-permission android:name="android.permission.READ_CONTACTS" />

C <uses-permission android:name="android.permission.CAMERA" />

D <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

💡 Hint

GPS needs precise location access.

ACCESS_FINE_LOCATION permission allows the app to access precise location data from GPS hardware.

❓ lifecycle

advanced

What happens if you start listening to location updates but forget to cancel the subscription?

In Flutter, if you subscribe to continuous location updates using a StreamSubscription but do not cancel it when the widget is disposed, what is the likely outcome?

A The app will crash immediately when the widget is disposed

B The subscription automatically cancels when the widget is disposed, so no problem occurs

C The app will leak memory and continue receiving location updates even after the widget is gone

D The location updates will stop but the app will freeze

💡 Hint

Think about resource cleanup in widget lifecycle.

Not cancelling a StreamSubscription causes it to keep running, leading to memory leaks and unnecessary processing.

❓ navigation

advanced

How to navigate to a screen showing a map with current location after permission granted?

You have a Flutter app that asks for location permission. After the user grants permission, you want to navigate to a MapScreen that shows the current location. Which code snippet correctly performs this navigation after permission is granted?

Flutter

Future<void> checkPermissionAndNavigate(BuildContext context) async {
  var status = await Geolocator.checkPermission();
  if (status == LocationPermission.denied) {
    status = await Geolocator.requestPermission();
  }
  if (status == LocationPermission.whileInUse || status == LocationPermission.always) {
    // Navigate to MapScreen
  }
}

A Navigator.push(context, MaterialPageRoute(builder: (_) => MapScreen()));

B Navigator.pop(context); Navigator.pushNamed(context, '/map');

C Navigator.pushReplacement(context, MaterialPageRoute(builder: (_) => MapScreen()));

D Navigator.pushNamedAndRemoveUntil(context, '/map', (route) => false);

💡 Hint

You want to add the MapScreen on top without removing previous screens.

Navigator.push adds a new screen on top of the current stack, which is appropriate after permission is granted.

📝 Syntax

expert

What error does this Flutter code produce when accessing location synchronously?

Consider this Flutter code snippet trying to get current location synchronously. What error will it cause?

Flutter

Position position = Geolocator.getCurrentPosition();
print('Lat: ${position.latitude}');

A TypeError: A Future was used where a Position was expected

B SyntaxError: Missing semicolon

C No error, prints latitude immediately

D RuntimeError: Location services disabled

💡 Hint

Check if getCurrentPosition returns a Future or a direct value.

getCurrentPosition() returns a Future, so assigning it directly to Position without await causes a type error.