Change reference to current class when setting the MethodChannel (#48806)

* Change reference to current class when setting the MethodChannel

* Added reference to MethodChannel and detach it from the engine

packages/flutter_tools/templates/plugin/android-java.tmpl/src/main/java/androidIdentifier/pluginClass.java.tmpl

@@ -16,10 +16,16 @@ import io.flutter.plugin.common.PluginRegistry.Registrar;
 
 /** {{pluginClass}} */
 public class {{pluginClass}} implements 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 MethodChannel channel;
+
   @Override
   public void onAttachedToEngine(@NonNull FlutterPluginBinding flutterPluginBinding) {
-    final MethodChannel channel = new MethodChannel(flutterPluginBinding.getFlutterEngine().getDartExecutor(), "{{projectName}}");
-    channel.setMethodCallHandler(new {{pluginClass}}());
+    channel = new MethodChannel(flutterPluginBinding.getFlutterEngine().getDartExecutor(), "{{projectName}}");
+    channel.setMethodCallHandler(this);
   }
 
   // This static function is optional and equivalent to onAttachedToEngine. It supports the old
@@ -47,6 +53,7 @@ public class {{pluginClass}} implements FlutterPlugin, MethodCallHandler {
 
   @Override
   public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
+    channel.setMethodCallHandler(null);
   }
 }
 {{/useAndroidEmbeddingV2}}

packages/flutter_tools/templates/plugin/android-kotlin.tmpl/src/main/kotlin/androidIdentifier/pluginClass.kt.tmpl

@@ -16,9 +16,15 @@ import io.flutter.plugin.common.PluginRegistry.Registrar
 
 /** {{pluginClass}} */
 public class {{pluginClass}}: 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) {
-    val channel = MethodChannel(flutterPluginBinding.getFlutterEngine().getDartExecutor(), "{{projectName}}")
-    channel.setMethodCallHandler({{pluginClass}}());
+    channel = MethodChannel(flutterPluginBinding.getFlutterEngine().getDartExecutor(), "{{projectName}}")
+    channel.setMethodCallHandler(this);
   }
 
   // This static function is optional and equivalent to onAttachedToEngine. It supports the old
@@ -47,6 +53,7 @@ public class {{pluginClass}}: FlutterPlugin, MethodCallHandler {
   }
 
   override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {
+    channel.setMethodCallHandler(null)
   }
 }
 {{/useAndroidEmbeddingV2}}