[federated_plugin] adds platform interface implementation and plugin implementation for Android (#503)

experimental/federated_plugin/federated_plugin_platform_interface/lib/federated_plugin_platform_interface.dart

@@ -0,0 +1,31 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:federated_plugin_platform_interface/location_method_channel.dart';
+import 'package:federated_plugin_platform_interface/location_model.dart';
+import 'package:plugin_platform_interface/plugin_platform_interface.dart';
+
+/// Interface which allows all the platform plugins to implement the same
+/// functionality.
+abstract class FederatedPluginInterface extends PlatformInterface {
+  FederatedPluginInterface() : super(token: _object);
+
+  static FederatedPluginInterface _federatedPluginInterface =
+      LocationMethodChannel();
+
+  static final Object _object = Object();
+
+  /// Provides instance of [LocationMethodChannel] to invoke platform calls.
+  static FederatedPluginInterface get instance => _federatedPluginInterface;
+
+  static set instance(FederatedPluginInterface instance) {
+    PlatformInterface.verifyToken(instance, _object);
+    _federatedPluginInterface = instance;
+  }
+
+  /// Returns [Location] to provide latitude and longitude.
+  Future<Location> getLocation() async {
+    throw UnimplementedError('getLocation() has not been implemented.');
+  }
+}

experimental/federated_plugin/federated_plugin_platform_interface/lib/location_method_channel.dart

@@ -0,0 +1,24 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:federated_plugin_platform_interface/federated_plugin_platform_interface.dart';
+import 'package:federated_plugin_platform_interface/location_model.dart';
+import 'package:flutter/services.dart';
+
+/// Implements [FederatedPluginInterface] using [MethodChannel] to fetch
+/// location from platform.
+class LocationMethodChannel extends FederatedPluginInterface {
+  static const MethodChannel _methodChannel = MethodChannel('location');
+
+  @override
+  Future<Location> getLocation() async {
+    final result =
+        await _methodChannel.invokeMethod<List<dynamic>>('getLocation');
+
+    return Location(
+      longitude: result.first as double,
+      latitude: result.last as double,
+    );
+  }
+}

experimental/federated_plugin/federated_plugin_platform_interface/lib/location_model.dart

@@ -0,0 +1,11 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/// Model to hold the incoming latitude and longitude values from platform.
+class Location {
+  final double latitude;
+  final double longitude;
+
+  Location({this.latitude, this.longitude});
+}