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.

Practice

1.

What is the main purpose of using the location feature in a Flutter app?

easy

A. To send text messages automatically

B. To change the device's screen brightness

C. To play music in the background

D. To find the device's current position on the map

Solution

1. Step 1: Understand location feature usage

   The location feature is used to get the device's position on Earth.

2. Step 2: Compare options with location purpose

   Only To find the device's current position on the map relates to finding the device's position, others are unrelated.

3. Final Answer:

   To find the device's current position on the map -> Option D

4. Quick Check:

   Location feature = Find position [OK]

Hint: Location means device position, not unrelated tasks [OK]

Common Mistakes:

• Confusing location with other device features
• Thinking location controls device settings
• Assuming location sends messages or plays music

2.

Which of the following is the correct way to request location permission in Flutter using the permission_handler package?

final status = await Permission.location.____();

easy

A. ask

B. request

C. get

D. allow

Solution

1. Step 1: Recall permission_handler syntax

   The package uses request() to ask for permission.

2. Step 2: Match method to code snippet

   Only request fits the method call to request permission.

3. Final Answer:

   request -> Option B

4. Quick Check:

   Permission request method = request() [OK]

Hint: Permission requests use request(), not ask or get [OK]

Common Mistakes:

• Using ask() instead of request()
• Confusing get() with permission request
• Using allow() which is not a method

3.

What will the following Flutter code print if the device's location is successfully fetched?

var location = await Geolocator.getCurrentPosition();
print('Lat: ${location.latitude}, Lon: ${location.longitude}');

medium

A. Lat: [some number], Lon: [some number]

B. Lat: 0.0, Lon: 0.0

C. SyntaxError

D. Lat: null, Lon: null

Solution

1. Step 1: Understand getCurrentPosition()

   This method returns the device's current latitude and longitude as numbers.

2. Step 2: Analyze print output

   The print statement outputs the latitude and longitude values, which are numbers, not null or zero by default.

3. Final Answer:

   Lat: [some number], Lon: [some number] -> Option A

4. Quick Check:

   getCurrentPosition() returns coordinates [OK]

Hint: getCurrentPosition() returns actual coordinates, not null [OK]

Common Mistakes:

• Assuming coordinates are zero or null by default
• Expecting syntax error from correct code
• Confusing method with one that returns null

4.

Identify the error in this Flutter code snippet that tries to get location updates:

StreamSubscription positionStream = Geolocator.getPositionStream().listen((Position position) {
  print(position.latitude);
});

positionStream.cancel();

medium

A. Missing permission check before listening to location stream

B. Using listen instead of subscribe

C. Calling cancel() immediately stops the stream

D. Position type should be String, not Position

Solution

1. Step 1: Check permission handling

   The code does not check or request location permission before starting the stream.

2. Step 2: Review other options

   Using listen is correct; cancel() is valid but should be called later; Position type is correct.

3. Final Answer:

   Missing permission check before listening to location stream -> Option A

4. Quick Check:

   Permission check required before location stream [OK]

Hint: Always check permission before accessing location stream [OK]

Common Mistakes:

• Skipping permission request before location access
• Confusing listen() with subscribe()
• Calling cancel() too early without reason
• Wrong type for position parameter

5.

You want your Flutter app to continuously track the user's location but only update the UI when the user moves more than 50 meters. Which approach is best?

hard

A. Use getCurrentPosition() repeatedly every second

B. Use getPositionStream() without filters and update UI every time

C. Use getPositionStream(distanceFilter: 50) to listen for updates

D. Use getLastKnownPosition() to get location once

Solution

1. Step 1: Understand continuous tracking with filtering

   The getPositionStream() method can listen for location changes and supports a distanceFilter to limit updates.

2. Step 2: Compare options for efficiency

   Use getPositionStream(distanceFilter: 50) to listen for updates uses distanceFilter: 50 to update only when user moves 50 meters, saving resources and avoiding UI overload.

3. Step 3: Eliminate other options

   Use getCurrentPosition() repeatedly every second is inefficient; C updates too often; D only gets location once.

4. Final Answer:

   Use getPositionStream(distanceFilter: 50) to listen for updates -> Option C

5. Quick Check:

   Use stream with distanceFilter for efficient updates [OK]

Hint: Use distanceFilter in stream to limit location updates [OK]

Common Mistakes:

• Polling location repeatedly instead of streaming
• Updating UI on every small location change
• Using getLastKnownPosition for continuous tracking