我需要从日期范围中检索天列表。用户选择开始日期和结束日期，并计算介于两者之间的天数（包括开始和结束时间）。
我尝试使用如下所示的for循环：
List<DateTime> calculateDaysInterval(DateTime startDate, DateTime endDate) {
List<DateTime> days = [];
for (DateTime d = startDate;
d.isBefore(endDate);
d.add(Duration(days: 1))) {
days.add(d);
}
return days;
}
但是它不起作用，它会冻结该应用程序。 你们有什么建议吗？ 预先感谢。
答案 0 :(得分：1)
我可能已经找到了解决方案。 看起来不太好，但是可以完成工作。
List<DateTime> calculateDaysInterval(DateTime startDate, DateTime endDate) {
List<DateTime> days = [];
for (int i = 0; i <= endDate.difference(startDate).inDays; i++) {
days.add(startDate.add(Duration(days: i)));
}
return days;
}
如果你们有更好的方法，请告诉我。
答案 1 :(得分：1)
效率可能不是最好的（实际上绝对不是效率），但是如果无论考虑夏时制，您必须绝对获得确切的天数，那将行得通。
DateTime startDate = new DateTime(2020, 3, 2);
DateTime endDate = new DateTime(2020, 3, 10);
List<DateTime> days = [];
DateTime tmp = DateTime(startDate.year, startDate.month, startDate.day, 12);
while(DateTime(tmp.year, tmp.month, tmp.day) != endDate){
days.add(DateTime(tmp.year, tmp.month, tmp.day));
tmp = tmp.add(new Duration(days: 1));
}
答案 2 :(得分：0)
我没有更改您的计算逻辑。
我只是提供了一种在日期范围过大时不阻止UI的方法。
使用计算或异步/等待功能，它将不会阻止UI。
由于计算功能只能通过map传递一个参数
我对计算进行了标记，因此您可以尝试使用计算或异步/等待
完整代码
import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:io';
import 'dart:core';
import 'dart:async';
import 'dart:convert';
import 'package:flutter/foundation.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();
}
Future<List<DateTime>> calculate() async {
var dateMap = {
"start": DateTime.parse("2019-01-01 20:18:04Z"),
"end": DateTime.parse("2019-01-10 20:18:04Z")
};
//return compute(calculateDaysInterval, dateMap);
var days = await calculateDaysInterval(dateMap);
for (var i=0; i<days.length; i++) {
print(days[i]);
}
}
List<DateTime> calculateDaysInterval(dynamic dateMap) {
var startDate = dateMap["start"];
var endDate = dateMap["end"];
print(startDate.toString());
print(endDate.toString());
List<DateTime> days = [];
for (int i = 0; i <= endDate.difference(startDate).inDays; i++) {
days.add(startDate.add(Duration(days: i)));
}
/* for (var i=0; i<days.length; i++) {
print(days[i]);
}*/
return days;
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() async{
/*var dateMap = {
"start": DateTime.parse("2019-01-01 20:18:04Z"),
"end": DateTime.parse("2019-01-10 20:18:04Z")
};*/
var days = await calculate();
/*for (var i=0; i<days.length; i++) {
print(days[i]);
}*/
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 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.
);
}
}
答案 3 :(得分：0)
怎么样：
final daysToGenerate = end.difference(start).inDays;
days = List.generate(daysToGenerate, (i) => DateTime(start.year, start.month, start.day + (i)));