问题
I am creating whole year calender, How to get numbers of days of month in Flutter? e.g., January -> 31, Fabruary -> 28/29(as per year), March -> 31 So on...
回答1:
You can use package https://pub.dev/packages/date_util
With dateUtility.daysInMonth
code snippet
var dateUtility = DateUtil();
var day1 = dateUtility.daysInMonth(2, 2019);
print(day1);
var day2 = dateUtility.daysInMonth(2, 2018);
print(day2);
full code
import 'package:flutter/material.dart';
import 'package:date_util/date_util.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
// This is the theme of your application.
//
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to Colors.green and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or simply save your changes to "hot reload" in a Flutter IDE).
// Notice that the counter didn't reset back to zero; the application
// is not restarted.
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
var dateUtility = DateUtil();
var day1 = dateUtility.daysInMonth(2, 2019);
print(day1);
var day2 = dateUtility.daysInMonth(2, 2018);
print(day2);
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
_counter++;
});
}
@override
Widget build(BuildContext context) {
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return Scaffold(
appBar: AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: Text(widget.title),
),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
// Column is also a layout widget. It takes a list of children and
// arranges them vertically. By default, it sizes itself to fit its
// children horizontally, and tries to be as tall as its parent.
//
// Invoke "debug painting" (press "p" in the console, choose the
// "Toggle Debug Paint" action from the Flutter Inspector in Android
// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
// to see the wireframe for each widget.
//
// Column has various properties to control how it sizes itself and
// how it positions its children. Here we use mainAxisAlignment to
// center the children vertically; the main axis here is the vertical
// axis because Columns are vertical (the cross axis would be
// horizontal).
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
Output
I/flutter (11462): 28
I/flutter (11462): 28
回答2:
Using date1.difference(date2).inDays is NOT correct. For some dates it will return incorrect results, like for DateTime(2020, 3).
This is because the Duration is based on seconds calculations. And inDays implementation is build with assumption that days are always have the same number of seconds (_duration ~/ Duration.microsecondsPerDay) which is not true.
But instead of this you can just use:
DateTime(date.year, date.month + 1, 0).day
回答3:
Without using any packages you could use this:
DateTime x1 = DateTime(2019,1,0).toUtc();
var y1 = DateTime(2019,2,0).toUtc().difference(x1).inDays;
回答4:
You can simply use the quiver.time library:
import 'package:quiver/time.dart';
daysInMonth(year, month);
回答5:
This should do it.
void main() {
var now = DateTime.now();
print(daysInMonth(now));
}
int daysInMonth(DateTime date){
var firstDayThisMonth = new DateTime(date.year, date.month, date.day);
var firstDayNextMonth = new DateTime(firstDayThisMonth.year, firstDayThisMonth.month + 1, firstDayThisMonth.day);
return firstDayNextMonth.difference(firstDayThisMonth).inDays;
}
prints:
30
回答6:
You can simply count duration in days without any third-party libs.
int daysInMonth = DateTimeRange(
start: date,
end: DateTime(date.year, date.month + 1))
.duration
.inDays;
来源：https://stackoverflow.com/questions/58762347/how-to-get-number-of-days-of-all-month-in-dart-flutter