flutter: non-Android: Prompt exit App manually when restoring default settings

src/ui/flutter_app/lib/l10n/intl_en.arb

@@ -608,6 +608,10 @@
   "@exitApp": {
     "description": "The App will exit."
   },
+  "exitAppManually": "You have to close immediately and reopen App to take effect.",
+  "@exitAppManually": {
+    "description": "You have to close immediately and reopen App to take effect."
+  },
   "pick": "Pick",
   "@pick": {
     "description": "Pick "

src/ui/flutter_app/lib/l10n/intl_zh.arb

@@ -152,6 +152,7 @@
   "restore": "重置",
   "restoreDefaultSettings": "恢复默认设置",
   "exitApp": "App 将退出。",
+  "exitAppManually": "您需要立即退出并重新打开本程序才能使默认配置生效。",
   "pick": "选择",
   "hint": "提示",
   "player": "玩家",

src/ui/flutter_app/lib/widgets/game_settings_page.dart

@@ -171,12 +171,24 @@ class _GameSettingsPageState extends State<GameSettingsPage> {
   restoreFactoryDefaultSettings() async {
     confirm() async {
       Navigator.of(context).pop();
-      _startTimer();
-      showCountdownDialog(context);
+      if (Platform.isAndroid) {
+        _startTimer();
+        showCountdownDialog(context);
+      } else {
+        _restore();
+        ScaffoldMessenger.of(context).showSnackBar(
+            SnackBar(content: Text(S.of(context).exitAppManually)));
+      }
     }
 
     cancel() => Navigator.of(context).pop();
 
+    var prompt = "";
+
+    if (Platform.isAndroid) {
+      prompt = S.of(context).exitApp;
+    }
+
     showDialog(
       context: context,
       builder: (BuildContext context) {
@@ -184,9 +196,7 @@ class _GameSettingsPageState extends State<GameSettingsPage> {
           title: Text(S.of(context).restore,
               style: TextStyle(color: AppTheme.dialogTitleColor)),
           content: SingleChildScrollView(
-            child: Text(S.of(context).restoreDefaultSettings +
-                "?\n" +
-                S.of(context).exitApp),
+            child: Text(S.of(context).restoreDefaultSettings + "?\n" + prompt),
           ),
           actions: <Widget>[
             TextButton(child: Text(S.of(context).ok), onPressed: confirm),