✨ Flutter Background Location Tracker Plugin Modernization

This contribution modernizes the Flutter Background Location Tracker plugin by replacing deprecated Android and iOS patterns with the latest plugin APIs, ensuring compatibility with Flutter embedding v2 while maintaining backward support for existing applications.

🔧 Key Changes Implemented

Android Implementation

• Updated BackgroundLocationTrackerPlugin.kt:

  • Migrated from Registrar, PluginRegistrantCallback, and ShimPluginRegistry to FlutterPlugin.FlutterPluginBinding.
  • Replaced PluginRegistrantCallback with a Kotlin lambda: (FlutterEngine) -> Unit.
  • Introduced a unified getFlutterEngine() method for consistent engine access.
  • Properly implemented onReattachedToActivityForConfigChanges() and onDetachedFromActivityForConfigChanges().
  • Deprecated legacy methods with @Deprecated annotations.

• Refactored FlutterBackgroundManager.kt:

  • Removed all usage of ShimPluginRegistry.
  • Adopted the new getFlutterEngine() utility for engine access.

iOS Implementation

• Enhanced SwiftBackgroundLocationTrackerPlugin.swift:

  • Replaced flutterPluginRegistrantCallback with an array of registrants (pluginRegistrants).
  • Updated engine initialization to loop through all registered registrants.
  • Created createMethodChannel(binaryMessenger:) for flexible channel creation.

• Improved ForegroundChannel.swift:

  • Added createMethodChannel(binaryMessenger:) method.
  • Marked getMethodChannel(with:) as deprecated but retained it for backward compatibility.

• Updated BackgroundLocationTrackerPlugin.m:

  • Added deprecation comments for clarity around older method usage.

Documentation & Examples

• README.md Updates:

  • Added a Migration Guide section.
  • Clarified differences between old and new plugin APIs.
  • Explained embedding v2 patterns and rationale.

• Example App Improvements:

  • Introduced a custom Application.kt in the Android example.
  • Annotated iOS AppDelegate.swift with V2 pattern examples.
  • Provided dual examples for legacy and modern plugin registration patterns.