return purchases screen

lib/base/base_state.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:io';
 
 import 'package:checker/resources.dart';
 import 'package:flutter/material.dart';
@@ -10,7 +11,6 @@ import 'package:checker/screens/faq.dart';
 import 'package:checker/strings.dart';
 import 'package:checker/db.dart';
 import 'package:flutter/rendering.dart';
-import 'package:meta/meta.dart';
 
 abstract class BaseState<T extends StatefulWidget> extends State<T> {
 
@@ -78,7 +78,14 @@ abstract class BaseState<T extends StatefulWidget> extends State<T> {
       child: getMenuItem(help_png, StringsLocalization.help())
     ));
 
-    if (Theme.of(context).platform != TargetPlatform.iOS) {
+    if(showReturnScreen()) {
+      menuItemList.add(new PopupMenuItem(
+        value: 3,
+        child: getMenuItem(exit_png, StringsLocalization.returnLabel())
+      ));
+    }
+
+    if (Platform.isAndroid) {
       menuItemList.add(new PopupMenuItem(
         value: 2,
         child: getMenuItem(exit_png, StringsLocalization.exit())
@@ -95,6 +102,8 @@ abstract class BaseState<T extends StatefulWidget> extends State<T> {
     ];
   }
 
+  bool showReturnScreen() => false;
+
   void onOptionsItemClick(int index) {
     switch (index) {
       case 0: {
@@ -119,9 +128,14 @@ abstract class BaseState<T extends StatefulWidget> extends State<T> {
         platform.invokeMethod('finish');
         break;
       }
+      case 3:
+        openReturnScreen();
+        break;
     }
   }
 
+  void openReturnScreen() {}
+
   /// Возвращает пункт меню (Картинка с текстом)
   Widget getMenuItem(String image, String text) {
     return new Row(children: [