- Add Linter rules for return types and final fields

- Enhance exception_handler code
- Add ShareUtil to unify modification point

lib/src/screens/dashboard/widgets/address_page.dart

@@ -1,10 +1,8 @@
 import 'package:cake_wallet/src/screens/base_page.dart';
-import 'package:cake_wallet/src/widgets/alert_with_one_action.dart';
 import 'package:cake_wallet/src/widgets/alert_with_two_actions.dart';
 import 'package:cake_wallet/src/widgets/keyboard_done_button.dart';
-import 'package:cake_wallet/src/widgets/primary_button.dart';
-import 'package:cake_wallet/store/settings_store.dart';
 import 'package:cake_wallet/themes/theme_base.dart';
+import 'package:cake_wallet/utils/share_util.dart';
 import 'package:cake_wallet/utils/show_pop_up.dart';
 import 'package:cake_wallet/view_model/dashboard/dashboard_view_model.dart';
 import 'package:flutter/material.dart';
@@ -15,7 +13,6 @@ import 'package:cake_wallet/generated/i18n.dart';
 import 'package:flutter_mobx/flutter_mobx.dart';
 import 'package:keyboard_actions/keyboard_actions.dart';
 import 'package:mobx/mobx.dart';
-import 'package:share_plus/share_plus.dart';
 
 class AddressPage extends BasePage {
   AddressPage({
@@ -101,11 +98,9 @@ class AddressPage extends BasePage {
         splashColor: Colors.transparent,
         iconSize: 25,
         onPressed: () {
-          final box = context.findRenderObject() as RenderBox?;
-
-          Share.share(
-            addressListViewModel.address.address,
-            sharePositionOrigin: box!.localToGlobal(Offset.zero) & box.size,
+          ShareUtil.share(
+            text: addressListViewModel.address.address,
+            context: context,
           );
         },
         icon: shareImage,

lib/src/screens/exchange_trade/exchange_trade_page.dart

@@ -305,7 +305,7 @@ class ExchangeTradeState extends State<ExchangeTradeForm> {
     _effectsInstalled = true;
   }
 
-  transactionStatePopup() {
+  void transactionStatePopup() {
     showPopUp<void>(
         context: context,
         builder: (BuildContext popupContext) {

lib/src/screens/receive/receive_page.dart

@@ -1,13 +1,11 @@
 import 'package:cake_wallet/src/widgets/keyboard_done_button.dart';
 import 'package:cake_wallet/src/widgets/section_divider.dart';
 import 'package:cake_wallet/themes/theme_base.dart';
+import 'package:cake_wallet/utils/share_util.dart';
 import 'package:cake_wallet/utils/show_pop_up.dart';
-import 'package:cake_wallet/view_model/dashboard/dashboard_view_model.dart';
 import 'package:cw_core/wallet_type.dart';
 import 'package:flutter/material.dart';
-import 'package:flutter/cupertino.dart';
 import 'package:flutter_mobx/flutter_mobx.dart';
-import 'package:share_plus/share_plus.dart';
 import 'package:cake_wallet/routes.dart';
 import 'package:cake_wallet/generated/i18n.dart';
 import 'package:cake_wallet/di.dart';
@@ -102,11 +100,9 @@ class ReceivePage extends BasePage {
             splashColor: Colors.transparent,
             iconSize: 25,
             onPressed: () {
-              final box = context.findRenderObject() as RenderBox?;
-
-              Share.share(
-                addressListViewModel.address.address,
-                sharePositionOrigin: box!.localToGlobal(Offset.zero) & box.size,
+              ShareUtil.share(
+                text: addressListViewModel.address.address,
+                context: context,
               );
             },
             icon: shareImage

lib/src/screens/seed/wallet_seed_page.dart

@@ -1,12 +1,11 @@
 import 'package:cake_wallet/palette.dart';
 import 'package:cake_wallet/themes/theme_base.dart';
 import 'package:cake_wallet/src/widgets/alert_with_two_actions.dart';
+import 'package:cake_wallet/utils/share_util.dart';
 import 'package:cake_wallet/utils/show_bar.dart';
 import 'package:cake_wallet/utils/show_pop_up.dart';
-import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
-import 'package:share_plus/share_plus.dart';
 import 'package:flutter_mobx/flutter_mobx.dart';
 import 'package:cake_wallet/generated/i18n.dart';
 import 'package:cake_wallet/src/widgets/primary_button.dart';
@@ -160,11 +159,9 @@ class WalletSeedPage extends BasePage {
                               padding: EdgeInsets.only(right: 8.0),
                               child: PrimaryButton(
                                   onPressed: () {
-                                    final box = context.findRenderObject() as RenderBox?;
-
-                                    Share.share(
-                                      walletSeedViewModel.seed,
-                                      sharePositionOrigin: box!.localToGlobal(Offset.zero) & box.size,
+                                    ShareUtil.share(
+                                      text: walletSeedViewModel.seed,
+                                      context: context,
                                     );
                                   },
                                   text: S.of(context).save,