Question

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。

Answer 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。

Answer 2

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));
}

Answer 3

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.
    );
  }
}

Answer 4

怎么样：

final daysToGenerate = end.difference(start).inDays;
days = List.generate(daysToGenerate, (i) => DateTime(start.year, start.month, start.day + (i)));

飞镖/颤振：日期范围内的天数列表

4 个答案: