What is the correct way to add date picker in flutter app?

A simple app showcasing its use:

import 'dart:async';import 'package:flutter/material.dart';void main() => runApp(MyApp());class MyApp extends StatelessWidget {  @override  Widget build(BuildContext context) {    return MaterialApp(      title: 'Flutter Demo',      home: MyHomePage(title: 'Flutter Demo Home Page'),    );  }}class MyHomePage extends StatefulWidget {  MyHomePage({Key key, this.title}) : super(key: key);  final String title;  @override  _MyHomePageState createState() => _MyHomePageState();}class _MyHomePageState extends State<MyHomePage> {  DateTime selectedDate = DateTime.now();  Future<void> _selectDate(BuildContext context) async {    final DateTime picked = await showDatePicker(        context: context,        initialDate: selectedDate,        firstDate: DateTime(2015, 8),        lastDate: DateTime(2101));    if (picked != null && picked != selectedDate)      setState(() {        selectedDate = picked;      });  }  @override  Widget build(BuildContext context) {    return Scaffold(      appBar: AppBar(        title: Text(widget.title),      ),      body: Center(        child: Column(          mainAxisSize: MainAxisSize.min,          children: <Widget>[            Text("${selectedDate.toLocal()}".split(' ')[0]),            SizedBox(height: 20.0,),            RaisedButton(              onPressed: () => _selectDate(context),              child: Text('Select date'),            ),          ],        ),      ),    );  }}

And a Dartpad with it:

https://dartpad.dev/e5a99a851ae747e517b75ac221b73529

Flutter provides showDatePicker function to achieve this. It is part of flutter material library.

You can find complete documentation at showDatePicker.

You can also find implemented example here: Date and Time Picker

for time picker-

Declare this variable at class level

TimeOfDay selectedTime =TimeOfDay.now();

and call this method:-

Future<Null> _selectTime(BuildContext context) async {    final TimeOfDay picked_s = await showTimePicker(        context: context,        initialTime: selectedTime, builder: (BuildContext context, Widget child) {           return MediaQuery(             data: MediaQuery.of(context).copyWith(alwaysUse24HourFormat: false),            child: child,          );});    if (picked_s != null && picked_s != selectedTime )      setState(() {        selectedTime = picked_s;      });  }