Project Overview

The objective of this project is to develop a cross-platform mobile application using Flutter that blocks or identifies spam callers on both iOS and Android devices. The app will utilize platform-specific APIs and extensions to accomplish the spam blocking feature:

• iOS: Utilize the Call Directory Extension to block or identify spam calls.
• Android: Utilize Telephony and CallScreeningService APIs to intercept and block calls.

1. Project Structure

1.1 Flutter Project Setup

• Project Name: SpamCallerBlocker
• Folders:
  • lib/: Contains Flutter Dart code.
  • ios/: Contains iOS native code and Call Directory Extension.
  • android/: Contains Android native code for call blocking.
  • assets/: Contains assets like icons and UI images.
  • test/: Contains unit and widget tests.

2. Flutter Codebase

2.1 Flutter UI

• Main Screen:

  • Display a list of blocked numbers.
  • Options to add a number manually.
  • Option to import numbers from a list or an external database.
  • Button to update the spam number list.

• Flutter Packages:

  • provider or riverpod for state management.
  • http for API calls if needed (e.g., to retrieve a list of spam numbers from a server).
  • flutter_local_notifications for local notifications on Android.

2.2 Communication with Native Code

• Platform Channels:
  • Use platform channels to send and receive data between Flutter and the native code (iOS & Android).
  • Example: Passing the list of spam numbers from the Flutter UI to the Call Directory Extension on iOS and to the appropriate APIs on Android.

// Example Flutter to Native Channel
const platform = MethodChannel('com.example.spamcallerblocker/extension');

Future<void> updateSpamList(List<String> numbers) async {
  try {
    await platform.invokeMethod('updateSpamList', {"numbers": numbers});
  } catch (e) {
    print("Failed to update spam list: $e");
  }
}

3. iOS Implementation

3.1 Call Directory Extension Setup

• Create a Call Directory Extension:
  • In Xcode, add a new target for a Call Directory Extension to the existing Flutter project.
  • Configure the extension to manage a list of blocked and identified numbers.

3.2 Native iOS Code

• Swift/Objective-C:
  • Implement the logic to receive the list of spam numbers from Flutter via platform channels.
  • Store and manage these numbers within the Call Directory Extension.

// Example Swift code to handle the platform channel in iOS

@objc class CallDirectoryHandler: NSObject, CXCallDirectoryExtensionContext {
    let spamNumbers = UserDefaults.standard.array(forKey: "spamNumbers") as? [String] ?? []

    func updateSpamList(with numbers: [String]) {
        UserDefaults.standard.set(numbers, forKey: "spamNumbers")
    }

    func addSpamNumbers(to context: CXCallDirectoryExtensionContext) {
        for number in spamNumbers {
            if let phoneNumber = Int64(number) {
                context.addBlockingEntry(withNextSequentialPhoneNumber: phoneNumber)
            }
        }
    }
}

• Update the Call Directory:
  • Periodically update the spam numbers through the Call Directory Extension using the data passed from the Flutter app.

3.3 App Group (if needed)

• App Group:
  • If data sharing between the main app and the extension is necessary, consider setting up an App Group.

4. Android Implementation

4.1 Permissions

• Manifest Permissions:
  • Ensure the Android app has the necessary permissions to read call logs and block calls.
  • Example permissions: READ_CALL_LOG, ANSWER_PHONE_CALLS, READ_PHONE_STATE.

<uses-permission android:name="android.permission.READ_CALL_LOG" />
<uses-permission android:name="android.permission.ANSWER_PHONE_CALLS" />
<uses-permission android:name="android.permission.READ_PHONE_STATE" />

4.2 CallScreeningService

• Implement CallScreeningService:
  • Create a service to intercept incoming calls and block or identify spam calls based on the list received from Flutter.

public class CallBlockerService extends CallScreeningService {
    @Override
    public void onScreenCall(Call.Details callDetails) {
        String incomingNumber = callDetails.getHandle().getSchemeSpecificPart();

        // Check if the number is in the spam list
        if (isSpam(incomingNumber)) {
            CallResponse.Builder responseBuilder = new CallResponse.Builder();
            responseBuilder.setDisallowCall(true);
            respondToCall(callDetails, responseBuilder.build());
        }
    }
    
    private boolean isSpam(String phoneNumber) {
        // Implement logic to check if the number is spam
        return spamList.contains(phoneNumber);
    }
}

4.3 TelephonyManager (for older Android versions)

• For Devices on Android Below API 29:
  • Use TelephonyManager to monitor incoming calls and block them if necessary.

5. Testing and Deployment

5.1 Testing

• Unit Tests:
  • Write unit tests for the Flutter code to ensure that the list of spam numbers is handled correctly.
• Integration Tests:
  • Test the communication between Flutter and the native code on both platforms.

5.2 Deployment

• App Store & Google Play Compliance:
  • Ensure that the app complies with the respective app store guidelines, especially regarding permissions and access to sensitive data.
• Beta Testing:
  • Use TestFlight for iOS and Google Play's beta testing tools to gather feedback before public release.

6. Additional Features (Optional)

• Crowdsourcing Spam Numbers:
  • Allow users to report spam numbers, which can be added to a shared database.
• Push Notifications:
  • Notify users when a known spam number is blocked.
• Periodic Updates:
  • Implement a mechanism to periodically fetch the latest spam numbers from a server.

7. Conclusion

This project document outlines the architecture and development plan for a cross-platform spam caller blocker app using Flutter. By leveraging platform-specific APIs, we can effectively block or identify spam calls on both iOS and Android, ensuring user privacy and security.

Note: This project requires proficiency in both Flutter and native iOS/Android development due to the need for platform channels and native code integration.