changed difficulty logic

lib/widgets/difficulty_dropdown.dart

@@ -2,19 +2,26 @@ import 'package:flutter/material.dart';
 
 import '../models/difficulty.dart';
 
+typedef Intcallback = void Function(int);
+
 class DifficultyDropdown extends StatelessWidget {
-  const DifficultyDropdown({super.key});
+  const DifficultyDropdown({super.key, this.onChanged});
+  final Intcallback? onChanged;
 
   @override
   Widget build(BuildContext context) {
-    List<DropdownMenuEntry> dropdownMenuEntryList = Difficulty.difficulties
-        .map(
-          (e) => _toDropdownMenuEntry(Difficulty.difficulties.indexOf(e), e),
-        )
+    List<DropdownMenuEntry> dropdownMenuEntryList = DifficultyUtil.difficulties
+        .map((e) =>
+            _toDropdownMenuEntry(DifficultyUtil.difficulties.indexOf(e), e))
         .toList();
 
     return DropdownMenu(
       dropdownMenuEntries: dropdownMenuEntryList,
+      onSelected: (value) {
+        if (onChanged != null) {
+          onChanged!(value as int);
+        }
+      },
     );
   }