Platform channels (MethodChannel) in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output when calling a native method with MethodChannel?

Consider this Flutter code snippet that calls a native method named getBatteryLevel using MethodChannel. What will be the output shown in the Flutter app if the native side returns 85?

Flutter

final MethodChannel channel = MethodChannel('samples.flutter.dev/battery');

Future<void> getBatteryLevel() async {
  final int batteryLevel = await channel.invokeMethod('getBatteryLevel');
  print('Battery level is $batteryLevel%');
}

// Assume getBatteryLevel() is called and native returns 85

A Battery level is 85%

B Battery level is null%

C Battery level is 0%

D Error: Method not found

💡 Hint

Think about what the native side returns and how Flutter receives it.

The Flutter app calls the native method via MethodChannel. If the native side returns 85, Flutter receives it as an integer and prints 'Battery level is 85%'.

❓ lifecycle

intermediate

When should you set up the MethodChannel listener in Flutter?

In a Flutter app using MethodChannel to receive messages from native code, when is the best lifecycle moment to set up the setMethodCallHandler listener to avoid missing messages?

A Inside the <code>main()</code> function before runApp()

B Inside the <code>build()</code> method of a StatelessWidget

C Inside the <code>dispose()</code> method

D Inside the <code>initState()</code> method of a StatefulWidget

💡 Hint

Think about when the widget is first created and ready to handle messages.

Setting up the listener inside initState() ensures it is ready when the widget is active and avoids missing messages. build() can be called multiple times, dispose() is too late, and main() is before Flutter widgets exist.

📝 Syntax

advanced

What error does this Flutter MethodChannel code produce?

Examine this Flutter code snippet using MethodChannel. What error will it cause when run?

Flutter

final MethodChannel channel = MethodChannel('samples.flutter.dev/battery');

Future<void> getBatteryLevel() async {
  final int batteryLevel = await channel.invokeMethod('getBatteryLevel');
  print('Battery level is $batteryLevel%');
}

A SyntaxError due to missing semicolons

B No error, runs correctly

C Runtime error: Method not found

D TypeError: batteryLevel is null

💡 Hint

Check the punctuation carefully in Dart code.

Dart requires semicolons at the end of statements. Missing semicolons cause syntax errors.

❓ navigation

advanced

How to navigate after receiving a native message via MethodChannel?

You receive a message from native code via MethodChannel in Flutter. You want to navigate to a new screen named DetailsPage when the message arrives. Which code snippet correctly performs this navigation inside the setMethodCallHandler?

Flutter

channel.setMethodCallHandler((call) async {
  if (call.method == 'showDetails') {
    // Navigate to DetailsPage
  }
});

A All of the above are correct if context is available

B Navigator.of(context).push(MaterialPageRoute(builder: (_) => DetailsPage()));

C Navigator.pushNamed(context, '/details');

D Navigator.push(context, MaterialPageRoute(builder: (_) => DetailsPage()));

💡 Hint

Think about Flutter navigation methods and context availability.

Option B uses the correct syntax: `Navigator.of(context).push(...)`. Options B and C are invalid because `Navigator` does not have static `push` or `pushNamed` methods. Option B is incorrect. The key is having `BuildContext` accessible inside the handler.

🔧 Debug

expert

Why does Flutter not receive native messages via MethodChannel?

A developer sets up a MethodChannel in Flutter and native Android code to send messages. However, Flutter never receives the messages. Which is the most likely cause?

A Flutter does not have internet permission

B The native code uses a different thread to send messages

C The MethodChannel name strings do not match exactly between Flutter and native code

D The Flutter app is missing a MaterialApp widget

💡 Hint

Check the channel name carefully in both Flutter and native code.

MethodChannel communication depends on matching channel names exactly. If they differ, messages won't be received.