DropdownRoutePage should dispose the created ScrollController [Flutte…

packages/dropdown_button2/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## UNRELEASED
 
 - Fix errorStyle has no effect for DropdownButtonFormField2, closes #327.
+- DropdownRoutePage should dispose the created ScrollController [Flutter core].
 
 ## 3.0.0-beta.21
 

packages/dropdown_button2/lib/src/dropdown_menu.dart

@@ -17,6 +17,7 @@ class _DropdownMenu<T> extends StatefulWidget {
   const _DropdownMenu({
     super.key,
     required this.route,
+    required this.scrollController,
     required this.textDirection,
     required this.buttonRect,
     required this.constraints,
@@ -25,6 +26,7 @@ class _DropdownMenu<T> extends StatefulWidget {
   });
 
   final _DropdownRoute<T> route;
+  final ScrollController scrollController;
   final TextDirection? textDirection;
   final Rect buttonRect;
   final BoxConstraints constraints;
@@ -50,6 +52,7 @@ class _DropdownMenuState<T> extends State<_DropdownMenu<T>> {
   _DropdownItemButton<T> dropdownItemButton(int index) =>
       _DropdownItemButton<T>(
         route: widget.route,
+        scrollController: widget.scrollController,
         textDirection: widget.textDirection,
         buttonRect: widget.buttonRect,
         constraints: widget.constraints,
@@ -177,7 +180,7 @@ class _DropdownMenuState<T> extends State<_DropdownMenu<T>> {
                       platform: Theme.of(context).platform,
                     ),
                     child: PrimaryScrollController(
-                      controller: route.scrollController!,
+                      controller: widget.scrollController,
                       child: Theme(
                         data: Theme.of(context).copyWith(
                           scrollbarTheme: dropdownStyle.scrollbarTheme,

packages/dropdown_button2/lib/src/dropdown_menu_item.dart

@@ -124,6 +124,7 @@ class _DropdownItemButton<T> extends StatefulWidget {
   const _DropdownItemButton({
     super.key,
     required this.route,
+    required this.scrollController,
     required this.textDirection,
     required this.buttonRect,
     required this.constraints,
@@ -133,6 +134,7 @@ class _DropdownItemButton<T> extends StatefulWidget {
   });
 
   final _DropdownRoute<T> route;
+  final ScrollController scrollController;
   final TextDirection? textDirection;
   final Rect buttonRect;
   final BoxConstraints constraints;
@@ -163,7 +165,7 @@ class _DropdownItemButtonState<T> extends State<_DropdownItemButton<T>> {
         widget.mediaQueryPadding,
         widget.itemIndex,
       );
-      widget.route.scrollController!.animateTo(
+      widget.scrollController.animateTo(
         menuLimits.scrollOffset,
         curve: Curves.easeInOut,
         duration: const Duration(milliseconds: 100),

packages/dropdown_button2/lib/src/dropdown_route.dart

@@ -36,8 +36,6 @@ class _DropdownRoute<T> extends PopupRoute<_DropdownRouteResult<T>> {
   final DropdownSearchData<T>? searchData;
   final DropdownSeparator<T>? dropdownSeparator;
 
-  ScrollController? scrollController;
-
   @override
   Duration get transitionDuration => _kDropdownMenuDuration;
 
@@ -250,7 +248,7 @@ class _DropdownRoute<T> extends PopupRoute<_DropdownRouteResult<T>> {
   }
 }
 
-class _DropdownRoutePage<T> extends StatelessWidget {
+class _DropdownRoutePage<T> extends StatefulWidget {
   const _DropdownRoutePage({
     super.key,
     required this.route,
@@ -275,35 +273,50 @@ class _DropdownRoutePage<T> extends StatelessWidget {
   final bool enableFeedback;
 
   @override
-  Widget build(BuildContext context) {
-    assert(debugCheckHasDirectionality(context));
+  State<_DropdownRoutePage<T>> createState() => _DropdownRoutePageState<T>();
+}
+
+class _DropdownRoutePageState<T> extends State<_DropdownRoutePage<T>> {
+  late ScrollController _scrollController;
 
+  @override
+  void initState() {
+    super.initState();
     // Computing the initialScrollOffset now, before the items have been laid
     // out. This only works if the item heights are effectively fixed, i.e. either
     // DropdownButton.itemHeight is specified or DropdownButton.itemHeight is null
     // and all of the items' intrinsic heights are less than _kMenuItemHeight.
     // Otherwise the initialScrollOffset is just a rough approximation based on
     // treating the items as if their heights were all equal to _kMenuItemHeight.
-    if (route.scrollController == null) {
-      final _MenuLimits menuLimits = route.getMenuLimits(
-        buttonRect,
-        constraints.maxHeight,
-        mediaQueryPadding,
-        selectedIndex,
-      );
-      route.scrollController =
-          ScrollController(initialScrollOffset: menuLimits.scrollOffset);
-    }
+    final _MenuLimits menuLimits = widget.route.getMenuLimits(
+      widget.buttonRect,
+      widget.constraints.maxHeight,
+      widget.mediaQueryPadding,
+      widget.selectedIndex,
+    );
+    _scrollController =
+        ScrollController(initialScrollOffset: menuLimits.scrollOffset);
+  }
 
-    final TextDirection? textDirection = Directionality.maybeOf(context);
+  @override
+  void dispose() {
+    _scrollController.dispose();
+    super.dispose();
+  }
 
+  @override
+  Widget build(BuildContext context) {
+    assert(debugCheckHasDirectionality(context));
+
+    final TextDirection? textDirection = Directionality.maybeOf(context);
     final Widget menu = _DropdownMenu<T>(
-      route: route,
+      route: widget.route,
+      scrollController: _scrollController,
       textDirection: textDirection,
-      buttonRect: buttonRect,
-      constraints: constraints,
-      mediaQueryPadding: mediaQueryPadding,
-      enableFeedback: enableFeedback,
+      buttonRect: widget.buttonRect,
+      constraints: widget.constraints,
+      mediaQueryPadding: widget.mediaQueryPadding,
+      enableFeedback: widget.enableFeedback,
     );
 
     return MediaQuery.removePadding(
@@ -316,13 +329,13 @@ class _DropdownRoutePage<T> extends StatelessWidget {
         builder: (BuildContext context) {
           return CustomSingleChildLayout(
             delegate: _DropdownMenuRouteLayout<T>(
-              route: route,
+              route: widget.route,
               textDirection: textDirection,
-              buttonRect: buttonRect,
-              availableHeight: constraints.maxHeight,
-              mediaQueryPadding: mediaQueryPadding,
+              buttonRect: widget.buttonRect,
+              availableHeight: widget.constraints.maxHeight,
+              mediaQueryPadding: widget.mediaQueryPadding,
             ),
-            child: capturedThemes.wrap(menu),
+            child: widget.capturedThemes.wrap(menu),
           );
         },
       ),