flutter: Fix warnings

src/ui/flutter_app/lib/mill/position.dart

@@ -41,8 +41,8 @@ class StateInfo {
 class Position {
   GameResult result = GameResult.pending;
 
-  List<String> board = List<String>(sqNumber);
-  List<String> _grid = List<String>(7 * 7);
+  List<String> board = List.filled(sqNumber, "");
+  List<String> _grid = List.filled(7 * 7, "");
 
   GameRecorder recorder;
 
@@ -90,24 +90,24 @@ class Position {
   Move move;
 
   Position.boardToGrid() {
-    _grid = List<String>();
+    _grid = [];
     for (int sq = 0; sq < board.length; sq++) {
       _grid[squareToIndex[sq]] = board[sq];
     }
   }
 
   Position.gridToBoard() {
-    board = List<String>();
+    board = [];
     for (int i = 0; i < _grid.length; i++) {
       board[indexToSquare[i]] = _grid[i];
     }
   }
 
   Position.clone(Position other) {
-    _grid = List<String>();
+    _grid = [];
     other._grid.forEach((piece) => _grid.add(piece));
 
-    board = List<String>();
+    board = [];
     other.board.forEach((piece) => board.add(piece));
 
     recorder = other.recorder;

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

@@ -526,8 +526,8 @@ class _GamePageState extends State<GamePage> with RouteAware {
     );
   }
 
-  void showSnackbar(String message) {
-    var currentScaffold = globalScaffoldKey.currentState;
+  void showSnackBar(String message) {
+    //var currentScaffold = globalScaffoldKey.currentState;
     ScaffoldMessenger.of(context).hideCurrentSnackBar();
     ScaffoldMessenger.of(context)
         .showSnackBar(SnackBar(content: Text(message)));
@@ -535,7 +535,7 @@ class _GamePageState extends State<GamePage> with RouteAware {
 
   Widget createOperatorBar() {
     //
-    final buttonStyle = TextStyle(color: UIColors.primaryColor, fontSize: 20);
+    //final buttonStyle = TextStyle(color: UIColors.primaryColor, fontSize: 20);
     final text = Game.shared.position.manualText;
 
     final manualStyle =
@@ -579,7 +579,7 @@ class _GamePageState extends State<GamePage> with RouteAware {
                     child: Text(S.of(context).copy, style: manualStyle),
                     onPressed: () =>
                         Clipboard.setData(ClipboardData(text: text)).then((_) {
-                      showSnackbar(S.of(context).moveHistoryCopied);
+                      showSnackBar(S.of(context).moveHistoryCopied);
                     }),
                   ),
                   TextButton(

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

@@ -28,8 +28,6 @@ class RuleSettingsPage extends StatefulWidget {
 }
 
 class _RuleSettingsPageState extends State<RuleSettingsPage> {
-  String _version = "";
-
   @override
   void initState() {
     super.initState();