Platform channels (MethodChannel) in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a MethodChannel with the name 'samples.flutter.dev/battery'.

Flutter

static const platform = MethodChannel('[1]');

Drag options to blanks, or click blank then click option'

Asamples.flutter.battery

Bflutter.dev/battery

Csamples.flutter.dev/battery

Dbattery.flutter.dev

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong or incomplete channel name.

Missing parts of the channel string.

The MethodChannel name must match exactly between Flutter and native code. Here, 'samples.flutter.dev/battery' is the correct channel name.

2fill in blank

medium

Complete the code to invoke the native method 'getBatteryLevel' asynchronously.

Flutter

final int batteryLevel = await platform.[1]('getBatteryLevel');

Drag options to blanks, or click blank then click option'

AexecuteMethod

BsendMethod

CcallMethod

DinvokeMethod

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent method like callMethod.

Forgetting to await the asynchronous call.

The correct method to call native code asynchronously is invokeMethod.

3fill in blank

hard

Fix the error in the code by completing the catch block to handle PlatformException.

Flutter

try {
  final int batteryLevel = await platform.invokeMethod('getBatteryLevel');
} on [1] catch (e) {
  print('Failed to get battery level: $e');
}

Drag options to blanks, or click blank then click option'

APlatformException

BException

CError

DMethodChannelException

Attempts:

3 left

💡 Hint

Common Mistakes

Catching generic Exception instead of PlatformException.

Using a non-existent exception class.

The native platform errors are caught as PlatformException in Flutter.

4fill in blank

hard

Fill both blanks to send an argument map with key 'charging' and value true to native code.

Flutter

final bool isCharging = await platform.invokeMethod('isCharging', [1]);

Drag options to blanks, or click blank then click option'

A{'charging': false}

B{'charging': true}

C['charging', true]

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Sending a list instead of a map.

Sending just a boolean without a key.

The argument must be a map with key 'charging' and value true to send data properly.

5fill in blank

hard

Fill all three blanks to define a MethodChannel, invoke 'getBatteryLevel', and handle exceptions properly.

Flutter

static const platform = MethodChannel('[1]');

Future<int> getBatteryLevel() async {
  try {
    final int batteryLevel = await platform.[2]('getBatteryLevel');
    return batteryLevel;
  } on [3] catch (e) {
    return -1;
  }
}

Drag options to blanks, or click blank then click option'

Asamples.flutter.dev/battery

BinvokeMethod

CPlatformException

DcallMethod

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong channel name or method name.

Catching wrong exception type.

Not awaiting the method call.

This code creates a MethodChannel with the correct name, calls the native method asynchronously, and catches PlatformException to handle errors.

Practice

1. What is the main purpose of MethodChannel in Flutter?

easy

A. To manage app navigation

B. To communicate between Flutter and native platform code

C. To create UI widgets in Flutter

D. To handle Flutter animations

Solution

1. Step 1: Understand Flutter and native code interaction

   Flutter apps sometimes need to use features only available in native code like Android or iOS.

2. Step 2: Role of MethodChannel

   MethodChannel is the way Flutter sends messages to native code and gets results back.

3. Final Answer:

   To communicate between Flutter and native platform code -> Option B

4. Quick Check:

   MethodChannel = Flutter-native communication [OK]

Hint: MethodChannel connects Flutter with native code [OK]

Common Mistakes:

• Thinking MethodChannel creates UI widgets
• Confusing MethodChannel with navigation or animation
• Assuming MethodChannel runs only in Flutter without native code

2. Which of the following is the correct way to create a MethodChannel in Flutter?

easy

A. var channel = new MethodChannel();

B. MethodChannel channel = MethodChannel();

C. MethodChannel channel = MethodChannel('com.example.channel');

D. var channel = MethodChannel.create('channel');

Solution

1. Step 1: Check MethodChannel constructor usage

   The constructor requires a string name to identify the channel, e.g., 'com.example.channel'.

2. Step 2: Validate options

   MethodChannel channel = MethodChannel('com.example.channel'); correctly uses MethodChannel('com.example.channel'). Options A, C, and D are invalid syntax or missing required parameters.

3. Final Answer:

   MethodChannel channel = MethodChannel('com.example.channel'); -> Option C

4. Quick Check:

   MethodChannel needs a channel name string [OK]

Hint: MethodChannel constructor needs a channel name string [OK]

Common Mistakes:

• Omitting the channel name string
• Using 'new' keyword unnecessarily
• Calling non-existent create() method

3. Given this Flutter code snippet, what will be printed if the native side returns the string "Hello from native"?

final channel = MethodChannel('com.example.channel');
String message = await channel.invokeMethod('greet');
print(message);

medium

A. null

B. Empty string

C. An error message

D. "Hello from native"

Solution

1. Step 1: Understand invokeMethod behavior

   The invokeMethod sends a message to native code and waits for a response.

2. Step 2: Native returns "Hello from native" string

   The returned string is assigned to message and printed.

3. Final Answer:

   "Hello from native" -> Option D

4. Quick Check:

   invokeMethod returns native response string [OK]

Hint: invokeMethod returns native response awaited as result [OK]

Common Mistakes:

• Assuming invokeMethod returns null if native responds
• Expecting invokeMethod to print automatically
• Ignoring await causing Future object print

4. What is wrong with this Flutter code snippet for calling native code?

final channel = MethodChannel('com.example.channel');
channel.invokeMethod('getData');
print('Data received');

medium

A. invokeMethod is not awaited, so print runs before data arrives

B. MethodChannel name is invalid

C. invokeMethod requires a callback parameter

D. print statement syntax is incorrect

Solution

1. Step 1: Check asynchronous call usage

   invokeMethod returns a Future and should be awaited to get the result before proceeding.

2. Step 2: Analyze print timing

   Without await, print('Data received') runs immediately, before native response arrives.

3. Final Answer:

   invokeMethod is not awaited, so print runs before data arrives -> Option A

4. Quick Check:

   Always await invokeMethod for native response [OK]

Hint: Always await invokeMethod to get native result before next code [OK]

Common Mistakes:

• Not awaiting invokeMethod causing timing issues
• Thinking MethodChannel name is invalid without reason
• Expecting invokeMethod to take a callback parameter

5. You want to send a message from Flutter to native Android code to get battery level. Which steps are needed to implement this using MethodChannel? Choose the correct sequence.

hard

A. 1. Create MethodChannel in Flutter with a name
2. Call invokeMethod('getBatteryLevel')
3. In Android native code, set MethodCallHandler on same channel name
4. Handle 'getBatteryLevel' method and return battery level
5. Flutter receives battery level response

B. 1. Create MethodChannel in Flutter with a name
2. Directly access Android battery API from Flutter
3. No native code needed
4. Flutter gets battery level

C. 1. Create MethodChannel in Flutter
2. Call invokeMethod without method name
3. Android native code listens on different channel name
4. Return battery level

D. 1. Use Flutter plugin battery package
2. No need to write native code or MethodChannel
3. Flutter gets battery level

Solution

1. Step 1: Setup MethodChannel in Flutter

   Create a channel with a unique name to communicate with native code.

2. Step 2: Call invokeMethod with method name

   Flutter sends 'getBatteryLevel' request to native side.

3. Step 3: Setup native Android MethodCallHandler

   Native code listens on the same channel name and handles method calls.

4. Step 4: Native code returns battery level

   Native side gets battery info and sends it back.

5. Step 5: Flutter receives and uses battery level

   Flutter awaits response and uses the data.

6. Final Answer:

   1. Create MethodChannel in Flutter with a name 2. Call invokeMethod('getBatteryLevel') 3. In Android native code, set MethodCallHandler on same channel name 4. Handle 'getBatteryLevel' method and return battery level 5. Flutter receives battery level response -> Option A

7. Quick Check:

   Flutter-native communication needs matching channel and method handling [OK]

Hint: Match channel name and method handler on both sides [OK]

Common Mistakes:

• Skipping native code setup for MethodCallHandler
• Calling invokeMethod without method name
• Using different channel names on Flutter and native sides