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Fix scrolling issues in CupertinoPicker #3678

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merged 2 commits into from
Jul 27, 2024
Merged

Fix scrolling issues in CupertinoPicker #3678

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b2bf206
fix scrolling issue in `CupertinoPicker`
ndonkoHenri Jul 20, 2024
351004c
move vars out of _manageScroll
ndonkoHenri Jul 20, 2024
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44 changes: 40 additions & 4 deletions packages/flet/lib/src/controls/cupertino_picker.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,44 @@ 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
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
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}");
Expand All @@ -43,7 +81,6 @@ class _CupertinoPickerControlState extends State<CupertinoPickerControl> {
}).toList();

double itemExtent = widget.control.attrDouble("itemExtent", _kItemExtent)!;
int? selectedIndex = widget.control.attrInt("selectedIndex");
double diameterRatio =
widget.control.attrDouble("diameterRatio", _kDefaultDiameterRatio)!;
double magnification = widget.control.attrDouble("magnification", 1.0)!;
Expand All @@ -54,6 +91,7 @@ class _CupertinoPickerControlState extends State<CupertinoPickerControl> {
Color? backgroundColor = widget.control.attrColor("bgColor", context);

Widget picker = CupertinoPicker(
scrollController: scrollController,
backgroundColor: backgroundColor,
diameterRatio: diameterRatio,
magnification: magnification,
Expand All @@ -63,14 +101,12 @@ class _CupertinoPickerControlState extends State<CupertinoPickerControl> {
useMagnifier: useMagnifier,
looping: looping,
onSelectedItemChanged: (int index) {
_index = index;
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suggestion: Consider using setState when updating _index.

To ensure the UI updates correctly, consider wrapping the assignment of _index in a setState call.

Suggested change
_index = index;
setState(() {
_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,
);

Expand Down