Complete Code for Cupertino Picker

cupertinopicker.dart

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

void main() {
  runApp(CupertinoExample());
}

class CupertinoExample extends StatefulWidget {
  @override
  _CupertinoExampleState createState() => _CupertinoExampleState();
}

class _CupertinoExampleState extends State<CupertinoExample> {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(debugShowCheckedModeBanner: false, home: ExamplePage());
  }
}

class ExamplePage extends StatefulWidget {
  @override
  _ExamplePageState createState() => _ExamplePageState();
}

class _ExamplePageState extends State<ExamplePage> {
  DateTime _setDate = DateTime.now();
  Duration initialtimer = new Duration();
  int selectitem = 1;

  Widget datetimePicker() {
    return CupertinoDatePicker(
      initialDateTime: DateTime.now(),
      onDateTimeChanged: (DateTime newdate) {
        print(newdate);
        setState(() {
          dateTime = newdate.day.toString() +
              '/' +
              newdate.month.toString() +
              '/' +
              newdate.year.toString() +
              ' ' +
              newdate.hour.toString() +
              ' hrs ' +
              newdate.minute.toString() +
              ' mins';
        });
      },
      use24hFormat: true,
      maximumDate: new DateTime(2021, 12, 30),
      minimumYear: 2010,
      maximumYear: 2021,
      minuteInterval: 1,
      mode: CupertinoDatePickerMode.dateAndTime,
    );
  }

  Widget timePicker() {
    return CupertinoTimerPicker(
      mode: CupertinoTimerPickerMode.hms,
      minuteInterval: 1,
      secondInterval: 1,
      initialTimerDuration: initialtimer,
      onTimerDurationChanged: (Duration changedtimer) {
        setState(() {
          initialtimer = changedtimer;
          time = changedtimer.inHours.toString() +
              ' hrs ' +
              (changedtimer.inMinutes % 60).toString() +
              ' mins ' +
              (changedtimer.inSeconds % 60).toString() +
              ' secs';
        });
      },
    );
  }

  Future<void> bottomSheet(BuildContext context, Widget child,
      {double height}) {
    return showModalBottomSheet(
        isScrollControlled: false,
        shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.only(
                topLeft: Radius.circular(13), topRight: Radius.circular(13))),
        backgroundColor: Colors.white,
        context: context,
        builder: (context) => Container(
            height: height ?? MediaQuery.of(context).size.height / 3,
            child: child));
  }

  Widget button(String text, {Function onPressed, Color color}) {
    return Container(
      width: 200,
      height: 50,
      margin: EdgeInsets.symmetric(vertical: 5),
      color: color ?? Colors.redAccent,
      child: MaterialButton(
          child: Text(
            '$text',
            style: TextStyle(color: Colors.white),
          ),
          onPressed: onPressed),
    );
  }

  String time;
  String dateTime;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        color: Colors.white,
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              button(
                "Cupertino date Picker",
                onPressed: () {
                  bottomSheet(context, datetimePicker());
                },
              ),
              dateTime == null ? Container() : Text('$dateTime'),
              button(
                "Cupertino Timer Picker",
                color: Colors.green,
                onPressed: () {
                  bottomSheet(context, timePicker());
                },
              ),
              time == null ? Container() : Text('$time'),
              button(
                "Cupertino Picker",
                color: Colors.blueAccent,
                onPressed: () {
                  Widget child = Scaffold(
                      appBar: AppBar(
                        title: Text(
                          "CupertinoPicker",
                          textAlign: TextAlign.justify,
                        ),
                        backgroundColor: Colors.teal,
                        actions: <Widget>[
                          IconButton(
                            icon: Icon(Icons.send),
                            onPressed: () {},
                          )
                        ],
                      ),
                      body: Container(
                        child: CupertinoPicker(
                          magnification: 1.2,
                          backgroundColor: Colors.black87,
                          children: <Widget>[
                            Text(
                              "TextWidget",
                              style:
                                  TextStyle(color: Colors.white, fontSize: 20),
                            ),
                            button(
                              'Button Widget',
                            ),
                            IconButton(
                              icon: Icon(Icons.home),
                              color: Colors.white,
                              iconSize: 40,
                              onPressed: () {},
                            )
                          ],
                          itemExtent: 80, //height of each item
                          looping: true,
                          onSelectedItemChanged: (int index) {
                            selectitem = index;
                          },
                        ),
                      ));
                  bottomSheet(context, child,
                      height: MediaQuery.of(context).size.height / 2);
                },
              )
            ],
          ),
        ),
      ),
    );
  }
}