如何动态地按日期排序？

如何解决如何动态地按日期排序？

我正在开发一个待办事项列表应用程序，我想按日期对上传的任务进行排序（新任务首先出现）。为此，我认为应该为“待办事项”列表中的每个上传项目提供一个密钥，并且该密钥应包含一个“日期”。为了做到这一点，在React Native中，我向按日期排序的列表中的数据添加了一个功能，但是由于我不熟悉，所以我不知道该怎么做。任何想法都可以帮助：）

main.dart

  List<String> _toDoItems = []; //this is the array in which the uploaded tasks are stored,btw Im not using any database.
  TextEditingController _controller = TextEditingController();

  void _addToDoItem(String task) {
    if(task.length > 0) {
      setState(() {  
        _toDoItems.add(task);
      });
    }
  }

  void _removeTodoItem(int index) {
    setState(() => _toDoItems.removeAt(index));
  }

  Widget _buildToDoItem(String toDoText,int index) {
    return SizedBox(
      child: Container(
        height: 58,margin: EdgeInsets.only(left: 22.0,right: 22.0,bottom: 12,),decoration: BoxDecoration(
          border: Border.all(width: 1.5,color: Colors.red),borderRadius: BorderRadius.all(Radius.circular(18)),child: Row(
          crossAxisAlignment: CrossAxisAlignment.center,children:[
            Expanded(
              child: ListTile(
                title: Text(
                  toDoText,style: TextStyle(fontSize: 18),onTap: () => _removeTodoItem(index),FlatButton(
              child: Text('Delete',style: TextStyle(color: Colors.red,fontSize: 16.5),onPressed: () => _removeTodoItem(index),],);
  }
  Widget _buildToDoList() {
    return Expanded(
      child: ListView.builder(
        itemBuilder: (context,index) {
          if (index < _toDoItems.length) {
            return _buildToDoItem(_toDoItems[index],index);
          }
        },);
  }
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: PreferredSize(
          preferredSize: Size.fromHeight(50),child: AppBar(
            centerTitle: true,backgroundColor: Colors.red,title: Text('To Do List',style: TextStyle(fontSize: 24,fontWeight: FontWeight.bold,)
        ),backgroundColor: Colors.white,body: Column(
            crossAxisAlignment: CrossAxisAlignment.center,children: [
              Container(
                height: 60,margin: EdgeInsets.all(22),child: Row(
                  crossAxisAlignment: CrossAxisAlignment.center,children: [
                    Expanded(
                      flex: 10,child: Container(
                        height: double.infinity,child: TextField(
                          controller: _controller,autofocus: true,onSubmitted: (val) {
                            _addToDoItem(val);
                            _controller.clear();
                          },style: TextStyle(fontSize: 18,Expanded(
                      flex: 4,margin: EdgeInsets.only(left: 12),child: RaisedButton(
                          textColor: Colors.white,color: Colors.red,child: Text('ADD',style: TextStyle(fontSize: 18)),shape: RoundedRectangleBorder(
                            borderRadius: BorderRadius.all(Radius.circular(12)),onPressed: () {
                            _addToDoItem(_controller.text);
                            _controller.clear();
                            FocusScope.of(context).requestFocus(FocusNode());
                          },_buildToDoList()
            ]
          ),);
  }

解决方法

您需要使用List的sort()方法，还需要能够在创建任务时以某种方式进行库存。

我已经用您发布的代码作为示例。使用它，您最后创建的元素将始终是列表的第一个。

import 'package:flutter/material.dart';

class ToDoElement {
  final String task;
  final DateTime timeOfCreation;

  ToDoElement(this.task,this.timeOfCreation);
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  createState() => _MyAppState();
}

class _MyAppState extends State {
  TextEditingController _controller = TextEditingController();
  List<ToDoElement> _toDoItems = [];

  void _removeTodoItem(int index) {
    setState(() => _toDoItems.removeAt(index));
  }

  void _addToDoItem(String task) {
    if (task.isNotEmpty) {
      setState(() => _toDoItems.add(ToDoElement(task,DateTime.now())));
    }
  }

  Widget _buildToDoItem(String toDoText,int index) {
    return SizedBox(
      child: Container(
        height: 58,margin: EdgeInsets.only(left: 22,right: 22,bottom: 12),decoration: BoxDecoration(
          border: Border.all(width: 1.5,color: Colors.red),borderRadius: BorderRadius.all(Radius.circular(18)),),child: Row(
          crossAxisAlignment: CrossAxisAlignment.center,children: [
            Expanded(
              child: ListTile(
                title: Text(
                  toDoText,style: TextStyle(fontSize: 18),onTap: () => _removeTodoItem(index),FlatButton(
              child: Text(
                'Delete',style: TextStyle(color: Colors.red,fontSize: 16.5),onPressed: () => _removeTodoItem(index),],);
  }

  int compareElement(ToDoElement a,ToDoElement b) =>
      a.timeOfCreation.isAfter(b.timeOfCreation) ? -1 : 1;

  Widget _buildToDoList() {
    _toDoItems.sort(compareElement);
    return Expanded(
      child: ListView.builder(
        itemCount: _toDoItems.length,itemBuilder: (context,index) {
          return _buildToDoItem(_toDoItems[index].task,index);
        },);
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: PreferredSize(
            preferredSize: Size.fromHeight(50),child: AppBar(
              centerTitle: true,backgroundColor: Colors.red,title: Text(
                'To Do List',style: TextStyle(
                  fontSize: 24,fontWeight: FontWeight.bold,)),backgroundColor: Colors.white,body: Column(crossAxisAlignment: CrossAxisAlignment.center,children: [
          Container(
            height: 60,margin: EdgeInsets.all(22),child: Row(
              crossAxisAlignment: CrossAxisAlignment.center,children: [
                Expanded(
                  flex: 10,child: Container(
                    height: double.infinity,child: TextField(
                      controller: _controller,autofocus: true,onSubmitted: (val) {
                        _addToDoItem(val);
                        _controller.clear();
                      },style: TextStyle(
                        fontSize: 18,Expanded(
                  flex: 4,margin: EdgeInsets.only(left: 12),child: RaisedButton(
                      textColor: Colors.white,color: Colors.red,child: Text('ADD',style: TextStyle(fontSize: 18)),shape: RoundedRectangleBorder(
                        borderRadius: BorderRadius.all(Radius.circular(12)),onPressed: () {
                        _addToDoItem(_controller.text);
                        _controller.clear();
                        FocusScope.of(context).requestFocus(FocusNode());
                      },_buildToDoList()
        ]),);
  }
}