CupertinoPicker example

main.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

void main() => runApp(
      MaterialApp(
        debugShowCheckedModeBanner: false,
        home: CupPickerDemo(),
      ),
    );

class CupPickerDemo extends StatefulWidget {
  final double itemExtent = 100;

  @override
  _CupPickerDemo createState() => _CupPickerDemo();
}

class _CupPickerDemo extends State<CupPickerDemo> {
  double total = 1;
  FixedExtentScrollController firstController;
  FixedExtentScrollController secondController;

  @override
  void initState() {
    super.initState();
    firstController = FixedExtentScrollController(initialItem: 0);
    secondController = FixedExtentScrollController(initialItem: 0);
  }

  @override
  void dispose() {
    firstController.dispose();
    secondController.dispose();
    super.dispose();
  }

  void _pickerHandler() {
    setState(
      () => total = (firstController.selectedItem + 1).toDouble() +
          (secondController.selectedItem == 0 ? 0 : .5),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Center(
          child: Text(
            total.toString(),
          ),
        ),
      ),
      body: Center(
        child: Row(
          children: <Widget>[
            Expanded(
              child: Center(
                child: CupertinoPicker(
                  itemExtent: widget.itemExtent,
                  scrollController: firstController,
                  onSelectedItemChanged: (int index) => _pickerHandler(),
                  children: List<Widget>.generate(10, (int index) {
                    return Center(
                      child: Text(
                        (++index).toString(),
                      ),
                    );
                  }),
                ),
              ),
            ),
            Expanded(
              child: Center(
                child: CupertinoPicker(
                  itemExtent: 100,
                  scrollController: secondController,
                  onSelectedItemChanged: (int index) => _pickerHandler(),
                  children: const <Widget>[
                    Center(
                      child: Text(
                        '.0',
                      ),
                    ),
                    Center(
                      child: Text(
                        '.5',
                      ),
                    ),
                  ],
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}