Picker

FutureBuilder<List<CategoryColor>>(
  future: GetIt.I<LocalDatabase>().getCategoryColors(),
  builder: (context, snapshot) {

		// selected color default to first one on start
		// it can be null during loading
    if (snapshot.hasData &&
        selectedColorId == null &&
        snapshot.data!.isNotEmpty) {
      selectedColorId = snapshot.data![0].id;
    }

    return _ColorPicker(
      colors: snapshot.hasData ? snapshot.data! : [],
      selectedColorId: selectedColorId,
			colorIdSetter: (int id){ // type defined by TypeDef and Function
				setState(() {
				  selectedColorId = id;
				};
			},
    );
  },
),

// when use                       // get selected as bool
colors.map((e) => renderColor(e, selectedColorId == e.id)).toList()
Dart
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typedef ColorIdSetter = void Function(int id);

@stless
final ColorIdSetter colorIdSetter;
	required this.colorIdSetter,

getDbData
  .map(
    (e) => GestureDetector(
      onTap: () {
        colorIdSetter(e.id);
      },
	)
Dart
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										// DB Table Class.   // if selected
Widget renderColor(CategoryColor color, bool isSelected) {
    return Container();
}
Dart
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define typedef outside the stless

pass in the id inside the typedef defined in No.1, under GestureDetector

pass in the function as parameter, the function must pass in the parameter stated inside the Function()