From b2bf206f13fa5bd9194c96f43fd33e4063adb2a8 Mon Sep 17 00:00:00 2001
From: ndonkoHenri <robotcoder4@protonmail.com>
Date: Sat, 20 Jul 2024 12:38:47 +0200
Subject: [PATCH 1/2] fix scrolling issue in `CupertinoPicker`

---
 .../lib/src/controls/cupertino_picker.dart    | 45 +++++++++++++++++--
 1 file changed, 41 insertions(+), 4 deletions(-)

diff --git a/packages/flet/lib/src/controls/cupertino_picker.dart b/packages/flet/lib/src/controls/cupertino_picker.dart
index f723d0ba3..bdf19ad61 100644
--- a/packages/flet/lib/src/controls/cupertino_picker.dart
+++ b/packages/flet/lib/src/controls/cupertino_picker.dart
@@ -30,6 +30,44 @@ class CupertinoPickerControl extends StatefulWidget {
 }
 
 class _CupertinoPickerControlState extends State<CupertinoPickerControl> {
+  int _index = 0;
+  FixedExtentScrollController scrollController = FixedExtentScrollController();
+
+  @override
+  void initState() {
+    super.initState();
+    scrollController = FixedExtentScrollController(
+        initialItem: widget.control.attrInt("selectedIndex", _index)!);
+    scrollController.addListener(_manageScroll);
+  }
+
+  void _manageScroll() {
+    // https://stackoverflow.com/a/75283541
+    // Fixes https://github.com/flet-dev/flet/issues/3649
+    int previousIndex = 0;
+    bool isScrollUp = false;
+    bool isScrollDown = true;
+    if (previousIndex != scrollController.selectedItem) {
+      isScrollDown = previousIndex < scrollController.selectedItem;
+      isScrollUp = previousIndex > scrollController.selectedItem;
+
+      var previousIndexTemp = previousIndex;
+      previousIndex = scrollController.selectedItem;
+
+      if (isScrollUp) {
+        scrollController.jumpToItem(previousIndexTemp - 1);
+      } else if (isScrollDown) {
+        scrollController.jumpToItem(previousIndexTemp + 1);
+      }
+    }
+  }
+
+  @override
+  void dispose() {
+    scrollController.dispose();
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     debugPrint("CupertinoPicker build: ${widget.control.id}");
@@ -43,7 +81,7 @@ class _CupertinoPickerControlState extends State<CupertinoPickerControl> {
     }).toList();
 
     double itemExtent = widget.control.attrDouble("itemExtent", _kItemExtent)!;
-    int? selectedIndex = widget.control.attrInt("selectedIndex");
+    int selectedIndex = widget.control.attrInt("selectedIndex", 0)!;
     double diameterRatio =
         widget.control.attrDouble("diameterRatio", _kDefaultDiameterRatio)!;
     double magnification = widget.control.attrDouble("magnification", 1.0)!;
@@ -54,6 +92,7 @@ class _CupertinoPickerControlState extends State<CupertinoPickerControl> {
     Color? backgroundColor = widget.control.attrColor("bgColor", context);
 
     Widget picker = CupertinoPicker(
+      scrollController: scrollController,
       backgroundColor: backgroundColor,
       diameterRatio: diameterRatio,
       magnification: magnification,
@@ -63,14 +102,12 @@ class _CupertinoPickerControlState extends State<CupertinoPickerControl> {
       useMagnifier: useMagnifier,
       looping: looping,
       onSelectedItemChanged: (int index) {
+        _index = index;
         widget.backend.updateControlState(
             widget.control.id, {"selectedIndex": index.toString()});
         widget.backend
             .triggerControlEvent(widget.control.id, "change", index.toString());
       },
-      scrollController: selectedIndex != null
-          ? FixedExtentScrollController(initialItem: selectedIndex)
-          : null,
       children: ctrls,
     );
 

From 351004c9eacd932d0dab86b0fd6b2f6b1122a864 Mon Sep 17 00:00:00 2001
From: ndonkoHenri <robotcoder4@protonmail.com>
Date: Sat, 20 Jul 2024 12:47:44 +0200
Subject: [PATCH 2/2] move vars out of _manageScroll

---
 packages/flet/lib/src/controls/cupertino_picker.dart | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/packages/flet/lib/src/controls/cupertino_picker.dart b/packages/flet/lib/src/controls/cupertino_picker.dart
index bdf19ad61..d5a26f80a 100644
--- a/packages/flet/lib/src/controls/cupertino_picker.dart
+++ b/packages/flet/lib/src/controls/cupertino_picker.dart
@@ -31,6 +31,9 @@ class CupertinoPickerControl extends StatefulWidget {
 
 class _CupertinoPickerControlState extends State<CupertinoPickerControl> {
   int _index = 0;
+  int previousIndex = 0;
+  bool isScrollUp = false;
+  bool isScrollDown = true;
   FixedExtentScrollController scrollController = FixedExtentScrollController();
 
   @override
@@ -44,9 +47,6 @@ class _CupertinoPickerControlState extends State<CupertinoPickerControl> {
   void _manageScroll() {
     // https://stackoverflow.com/a/75283541
     // Fixes https://github.com/flet-dev/flet/issues/3649
-    int previousIndex = 0;
-    bool isScrollUp = false;
-    bool isScrollDown = true;
     if (previousIndex != scrollController.selectedItem) {
       isScrollDown = previousIndex < scrollController.selectedItem;
       isScrollUp = previousIndex > scrollController.selectedItem;
@@ -81,7 +81,6 @@ class _CupertinoPickerControlState extends State<CupertinoPickerControl> {
     }).toList();
 
     double itemExtent = widget.control.attrDouble("itemExtent", _kItemExtent)!;
-    int selectedIndex = widget.control.attrInt("selectedIndex", 0)!;
     double diameterRatio =
         widget.control.attrDouble("diameterRatio", _kDefaultDiameterRatio)!;
     double magnification = widget.control.attrDouble("magnification", 1.0)!;