Context:
I'm trying to extend and implement a custom CupertinoSlidingSegmentedControl with some alterations.
Here is a great example of using the widget:
class _ViewState extends State<View> {
int segmentedControlGroupValue = 0;
final Map<int, Widget> myTabs = const <int, Widget>{
0: Text("Item 1"),
1: Text("Item 2")
};
@override
Widget build(BuildContext context) {
return Scaffold(
body: CupertinoSlidingSegmentedControl(
groupValue: segmentedControlGroupValue,
children: myTabs,
onValueChanged: (i) {
setState(() {
segmentedControlGroupValue = i;
});
}),
);
}
}
from @AidanMarshall's answer found here
What am I trying to do?
I am customizing the myTabs into a custom itemBuilder similarly to the ListView.builder implementation. My implementation should be used as follows:
SegmentedSlider<GenderPreference>(
values: GenderPreference.values,
thumbColor: Colors.blue, // or use a custom theme
onValueChanged: (value) {
// update profile information here
},
sliderItemBuilderFunction: (context, item, active) {
return Text(
GenderPreference.asString(item),
style: Theme.of(context).textTheme.subtitle2!.copyWith(
color: active
? Colors.white
: Colors.green,
),
);
},
selectedValue: GenderPreference.None,
)
With this, I am using my own sliderItemBuilderFunction function defined as follows:
typedef Widget ItemValueWidgetBuilder<T>(BuildContext context, T item, bool active);
this accepts the build context, the generic item T and a (is) active convenience field
Problem:
The problem is each time I run the widget, I get the following error for each item in values:
======== Exception caught by widgets library =======================================================
The following _TypeError was thrown building SegmentedSlider<GenderPreference>(dirty, dependencies: [_LocalizationsScope-[GlobalKey#0a25e], _InheritedTheme], state: _SegmentedSliderState<GenderPreference>#40901):
type '(BuildContext, GenderPreference, bool) => Text' is not a subtype of type '(BuildContext, dynamic, bool) => Widget'
The relevant error-causing widget was:
SegmentedSlider<GenderPreference> file:///C:/Users/CybeX/MyAwesomeApp/awesome-app-mobile-flutter/lib/viewcontrollers/profile/ui_profile.dart:309:20
When the exception was thrown, this was the stack:
#0 _SegmentedSliderState.build.<anonymous closure> (package:cozy_up/framework/ui/components/slider.dart:34:28)
#1 MappedListIterable.elementAt (dart:_internal/iterable.dart:412:31)
#2 ListIterator.moveNext (dart:_internal/iterable.dart:341:26)
#3 new _GrowableList._ofEfficientLengthIterable (dart:core-patch/growable_array.dart:188:27)
#4 new _GrowableList.of (dart:core-patch/growable_array.dart:150:28)
...
====================================================================================================
Reloaded 0 libraries in 1 536ms.
Question:
'(BuildContext, GenderPreference, bool) => Text' is not a subtype of type '(BuildContext, dynamic, bool) => Widget'
Firstly, the '(BuildContext, GenderPreference, bool) => Text' is my custom function, which should return a Widget as specified in the typedef.
Force Widget inside Slider's build function?
If I force this as a Widget with
Widget _widget = widget.sliderItemBuilderFunction(context, e, e == activeValue);
in my slider build function, I get exactly the same error.
Force Widget inside itemBuilder's function?
Further, if I return a Widget in my sliderItemBuilderFunction() implementation, I get the same error, but
'(BuildContext, GenderPreference, bool) => Widget' is not a subtype of type '(BuildContext, dynamic, bool) => Widget'
What am I doing wrong?
Enum Used
enum GenderPreference {
Male,
Female,
Other,
None,
}
extension GenderPreferenceExt on GenderPreference {
static const enums = {
GenderPreference.Male: 'Male',
GenderPreference.Female: 'Female',
GenderPreference.Other: 'Other',
GenderPreference.None: 'None',
};
static String asString(GenderPreference genderPreference) {
return enums[genderPreference] ?? "";
}
static GenderPreference parse(String _mode) {
if (_mode == "" || _mode == null) {
return GenderPreference.None;
}
return enums.entries
.where((element) => element.value.toLowerCase() == _mode.toLowerCase())
.first
.key;
}
}
Full Slider Implementation:
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
typedef Widget ItemValueWidgetBuilder<T>(
BuildContext context, T item, bool active);
class SegmentedSlider<T> extends StatefulWidget {
final Color backgroundColor;
final Color thumbColor;
final ValueChanged<T?> onValueChanged;
final T selectedValue;
final List<T> values;
final ItemValueWidgetBuilder<T> sliderItemBuilderFunction;
const SegmentedSlider(
{Key? key,
this.thumbColor = Colors.grey,
this.backgroundColor = Colors.white,
required this.onValueChanged,
required this.sliderItemBuilderFunction,
required this.selectedValue,
required this.values})
: super(key: key);
@override
_SegmentedSliderState<T> createState() => new _SegmentedSliderState<T>();
}
class _SegmentedSliderState<T> extends State<SegmentedSlider> {
late T activeValue;
@override
void initState() {
// TODO: implement initState
super.initState();
activeValue = widget.selectedValue;
}
@override
Widget build(BuildContext context) {
List<MapEntry<T, Widget>> map = widget.values.map((e) {
var _widget =
widget.sliderItemBuilderFunction(context, e, e == activeValue);
print(_widget);
return MapEntry<T, Widget>(e, Container());
}).toList();
Map<T, Widget> children = Map.fromEntries(map);
return CupertinoSlidingSegmentedControl<T>(
backgroundColor: widget.backgroundColor,
thumbColor: widget.thumbColor,
onValueChanged: (value) {
activeValue = value!;
widget.onValueChanged(value);
},
children: children,
groupValue: widget.selectedValue,
);
}
}
