How to calculate age from datepicker using flutter? - flutter

Question

In my code I used datepicker to selcte birthday .In date picker has a rang.And when the user select birthday and close the app and reopen later then also display that selected birthday.For that I used sharedprefernces , I want calculate age from birthday when the user select birthday then should automatically calculate age.
Image of UI
package
code
import 'package:age_calculator/age_calculator.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
class BirthdayScreen extends StatefulWidget {
const BirthdayScreen({Key? key}) : super(key: key);
#override
State<BirthdayScreen> createState() => _BirthdayScreenState();
}
class _BirthdayScreenState extends State<BirthdayScreen> {
// 1st dropdown button
#override
void initState() {
super.initState();
dropdownValueBirthday = birthday.first;
checkValueBirthday();
}
//date picker
DateTime? selectedDate;
DateTime now = new DateTime.now();
void showDatePicker() {
DateTime mindate = DateTime(now.year - 2, now.month, now.day - 29);
DateTime maxdate = DateTime(now.year - 1, now.month, now.day);
showCupertinoModalPopup(
context: context,
builder: (BuildContext builder) {
return Container(
height: MediaQuery.of(context).copyWith().size.height * 0.25,
color: Colors.white,
child: CupertinoDatePicker(
mode: CupertinoDatePickerMode.date,
initialDateTime: mindate,
onDateTimeChanged: (value) {
if (value != selectedDate) {
setState(() {
selectedDate = value;
dropdownValueBirthday =
'${selectedDate?.year}/${selectedDate?.month}/${selectedDate?.day} ';
calAge();
});
}
},
maximumDate: maxdate,
minimumDate: mindate,
),
);
});
}
String? dropdownValueBirthday;
List<String> birthday = [
'Birthday',
];
//IF "dropdownValueMembers" is empty pass "which" word as a initial value if al ready selected then pass the shared preference value
checkValueBirthday() {
_getDataBirthday();
}
_saveDataBirthday(String dropdownValueBirthdayShared) async {
SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
sharedPreferences.setString("dataBirthday", dropdownValueBirthdayShared);
}
_getDataBirthday() async {
SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
dropdownValueBirthday =
sharedPreferences.getString("dataBirthday") ?? birthday.first;
setState(() {});
}
String age = "";
DateDuration? duration;
getAge(DateTime fromDate) =>
DateTime.now().difference(fromDate).inDays ~/ 365;
void calAge() {
// DateTime birthday = DateTime.parse(dropdownValueBirthday!);
//
// setState(() {
// duration = AgeCalculator.age(birthday);
// });
DateTime? birt; // DateTime(1990);
if (birt != null) {
print('age from birt: ${getAge(birt)}');
} else {
print('birt is null');
}
}
#override
Widget build(BuildContext context) {
print(duration);
print(dropdownValueBirthday);
return Scaffold(
body: Container(
child: Column(
children: [
Center(
child: Padding(
padding: const EdgeInsets.only(left: 15, top: 100),
child: Row(
children: <Widget>[
const Icon(
Icons.brightness_1,
color: Colors.black,
size: 10,
),
const Padding(
padding: EdgeInsets.only(left: 15.0),
child: Text("birthday",
style: TextStyle(
fontSize: 16.0,
)),
),
Padding(
padding: const EdgeInsets.only(left: 25.0),
child: SizedBox(
width: 110.0,
height: 25.0,
child: DecoratedBox(
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(12),
color: Colors.white,
),
child: Center(
child: Text(
selectedDate == null
? (dropdownValueBirthday ?? birthday.first)
: '${selectedDate?.year}/${selectedDate?.month}/${selectedDate?.day} ',
style: const TextStyle(
fontSize: 16, fontWeight: FontWeight.w500),
),
),
),
),
),
Padding(
padding: const EdgeInsets.only(left: 15.0, top: 30.0),
child: SizedBox(
width: 88.0,
height: 25.0,
child: MaterialButton(
onPressed: showDatePicker,
shape: const StadiumBorder(),
color: Colors.blue,
child: const Text(
'select',
style: TextStyle(color: Colors.white, fontSize: 12),
),
),
),
),
],
),
),
),
Padding(
padding: const EdgeInsets.only(
bottom: 0.0,
),
child: SizedBox(
width: 160.0,
height: 35.0,
child: ElevatedButton(
style: ButtonStyle(
shape: MaterialStateProperty.all<RoundedRectangleBorder>(
RoundedRectangleBorder(
borderRadius: BorderRadius.circular(18.0),
side: const BorderSide(
color: Colors.blueAccent,
),
),
),
),
onPressed: () {
_saveDataBirthday(dropdownValueBirthday!);
// _saveDataAgree(isChecked!);
},
child: const Text('next')),
),
),
],
),
),
);
}
}
now display this

Answer 1

if (value != selectedDate) {
setState(() {
selectedDate = value;
if(value != null){
birt = DateTime.now().difference(value).inDays ~/ 365;
}
dropdownValueBirthday =
'${selectedDate?.year}/${selectedDate?.month}/${selectedDate?.day} ';
calAge();
});
and decalre the birt at the top Datetime? birt;
void calAge() {
// DateTime birthday = DateTime.parse(dropdownValueBirthday!);
//
// setState(() {
// duration = AgeCalculator.age(birthday);
// });
if (birt != null) {
print('age from birt: ${getAge(birt)}');
} else {
print('birt is null');
}
}

Answer 2

I haven't counted leap years but for me is acceptable.
/*
getAge(DateTime fromDate) => DateTime.now().difference(fromDate).inDays ~/ 365;
void main() {
DateTime? birt; // DateTime(1996);
if(birt != null){
print('age from birt: ${getAge(birt)}');
}else{
print('birt is null');
}
}
*/
getAge(DateTime? fromDate) => fromDate != null ? DateTime.now().difference(fromDate).inDays ~/ 365 : null;
void main() {
print('getAge result: ${getAge(null)}'); // getAge result: null
print('getAge result: ${getAge(DateTime(1990))}'); // getAge result: 32
print('getAge result: ${getAge(DateTime(2020))}'); // getAge result: 2
}