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

experimental/federated_plugin/federated_plugin/android/build.gradle

@@ -40,4 +40,5 @@ android {
 
 dependencies {
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
+    implementation 'com.google.android.gms:play-services-location:17.0.0'
 }

experimental/federated_plugin/federated_plugin/android/src/main/AndroidManifest.xml

@@ -1,3 +1,5 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="dev.flutter.federated_plugin">
+    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
+    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
 </manifest>

experimental/federated_plugin/federated_plugin/android/src/main/kotlin/dev/flutter/federated_plugin/FederatedPlugin.kt

@@ -4,37 +4,109 @@
 
 package dev.flutter.federated_plugin
 
-import androidx.annotation.NonNull;
+import android.Manifest
+import android.app.Activity
+import android.content.Context
+import android.content.pm.PackageManager
+import androidx.annotation.NonNull
+import androidx.core.app.ActivityCompat.requestPermissions
+import androidx.core.content.ContextCompat
+import com.google.android.gms.location.LocationServices.getFusedLocationProviderClient
 
 import io.flutter.embedding.engine.plugins.FlutterPlugin
+import io.flutter.embedding.engine.plugins.activity.ActivityAware
+import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding
 import io.flutter.plugin.common.MethodCall
 import io.flutter.plugin.common.MethodChannel
 import io.flutter.plugin.common.MethodChannel.MethodCallHandler
 import io.flutter.plugin.common.MethodChannel.Result
-import io.flutter.plugin.common.PluginRegistry.Registrar
+import io.flutter.plugin.common.PluginRegistry
 
-/** FederatedPlugin */
-public class FederatedPlugin: FlutterPlugin, MethodCallHandler {
-  /// The MethodChannel that will the communication between Flutter and native Android
-  ///
-  /// This local reference serves to register the plugin with the Flutter Engine and unregister it
-  /// when the Flutter Engine is detached from the Activity
-  private lateinit var channel : MethodChannel
 
-  override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
-    channel = MethodChannel(flutterPluginBinding.getFlutterEngine().getDartExecutor(), "federated_plugin")
-    channel.setMethodCallHandler(this);
-  }
+class FederatedPlugin : FlutterPlugin, MethodCallHandler, ActivityAware, PluginRegistry.RequestPermissionsResultListener {
+    private lateinit var channel: MethodChannel
+    private lateinit var context: Context
+    private lateinit var activity: Activity
+    private lateinit var result: Result
+    private val REQUEST_CODE = 1001
 
-  override fun onMethodCall(@NonNull call: MethodCall, @NonNull result: Result) {
-    if (call.method == "getPlatformVersion") {
-      result.success("Android ${android.os.Build.VERSION.RELEASE}")
-    } else {
-      result.notImplemented()
+    override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
+        channel = MethodChannel(flutterPluginBinding.binaryMessenger, "location")
+        channel.setMethodCallHandler(this)
+        context = flutterPluginBinding.applicationContext
     }
-  }
 
-  override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {
-    channel.setMethodCallHandler(null)
-  }
+    override fun onMethodCall(@NonNull call: MethodCall, @NonNull result: Result) {
+        this.result = result
+        if (call.method == "getLocation") {
+            // Check for the runtime permission if SDK version is greater than 23. If permissions
+            // are granted, send the location data back to Dart. If permissions are not granted,
+            // request for the runtime permissions.
+            if (android.os.Build.VERSION.SDK_INT > android.os.Build.VERSION_CODES.LOLLIPOP && !checkPermissions()) {
+                requestPermissions(activity, arrayOf(
+                        Manifest.permission.ACCESS_FINE_LOCATION,
+                        Manifest.permission.ACCESS_COARSE_LOCATION
+                ), REQUEST_CODE)
+            } else {
+                provideLocation()
+            }
+        } else {
+            result.notImplemented()
+        }
+    }
+
+    // Method to fetch and send the last known location of the device to Dart.
+    private fun provideLocation() {
+        getFusedLocationProviderClient(context).lastLocation
+                .addOnSuccessListener { location ->
+                    if (location != null) {
+                        result.success(listOf(location.longitude, location.latitude))
+                    } else {
+                        result.error("NOT_DETERMINED", "Not able to determine location", null)
+                    }
+                }.addOnFailureListener { exception ->
+                    result.error("Error", exception.message, null)
+                }
+    }
+
+    // Method to check permissions to access the location data.
+    private fun checkPermissions(): Boolean {
+        val fineLocationPermission = ContextCompat.checkSelfPermission(context, Manifest.permission.ACCESS_FINE_LOCATION)
+        val coarseLocationPermission = ContextCompat.checkSelfPermission(context, Manifest.permission.ACCESS_COARSE_LOCATION)
+
+        return fineLocationPermission == PackageManager.PERMISSION_GRANTED &&
+                coarseLocationPermission == PackageManager.PERMISSION_GRANTED
+    }
+
+
+    override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {
+        channel.setMethodCallHandler(null)
+    }
+
+    override fun onDetachedFromActivity() {}
+
+    override fun onReattachedToActivityForConfigChanges(binding: ActivityPluginBinding) {
+        activity = binding.activity
+    }
+
+    override fun onAttachedToActivity(binding: ActivityPluginBinding) {
+        activity = binding.activity
+        binding.addRequestPermissionsResultListener(this)
+    }
+
+    override fun onDetachedFromActivityForConfigChanges() {}
+
+    // Callback for the result after requesting for runtime permissions. If permissions
+    // are granted, send the location data, or send an error back to Dart if permissions
+    // are not granted.
+    override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>?, grantResults: IntArray): Boolean {
+        if (requestCode == REQUEST_CODE && grantResults.isNotEmpty()) {
+            if (grantResults[0] == PackageManager.PERMISSION_GRANTED && grantResults[1] == PackageManager.PERMISSION_GRANTED) {
+                provideLocation()
+            } else {
+                result.error("PERMISSION_DENIED", "Permission denied from User", null)
+            }
+        }
+        return false
+    }
 }