CODE EXAMPLE FOR DART

how to group data by date in a listview in flutter

import 'package:flutter/material.dart';
import 'package:intl/intl.dart';

void main() {
  final dateString = '2020-06-16T10:31:12.000Z';
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;
  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
 
  List<Map> list = [
    {
      "time": "2020-06-16T10:31:12.000Z",
      "message":
          "P2 BGM-01 HV buiten materieel (Gas lekkage) Franckstraat Arnhem 073631"
    },
    {
      "time": "2020-06-16T10:29:35.000Z",
      "message": "A1 Brahmslaan 3862TD Nijkerk 73278"
    },
    {
      "time": "2020-06-16T10:29:35.000Z",
      "message": "A2 NS Station Rheden Dr. Langemijerweg 6991EV Rheden 73286"
    },
    {
      "time": "2020-06-15T09:41:18.000Z",
      "message": "A2 VWS Utrechtseweg 6871DR Renkum 74636"
    },
    {
      "time": "2020-06-14T09:40:58.000Z",
      "message":
          "B2 5623EJ : Michelangelolaan Eindhoven Obj: ziekenhuizen 8610 Ca CATH route 522 PAAZ Rit: 66570"
    }
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: ListView.builder(
            itemCount: list.length,
            itemBuilder: (_, index) {
              bool isSameDate = true;
              final String dateString = list[index]['time'];
              final DateTime date = DateTime.parse(dateString);
              final item = list[index];
              if (index == 0) {
                isSameDate = false;
              } else {
                final String prevDateString = list[index - 1]['time'];
                final DateTime prevDate = DateTime.parse(prevDateString);
                isSameDate = date.isSameDate(prevDate);
              }
              if (index == 0 || !(isSameDate)) {
                return Column(children: [
                  Text(date.formatDate()),
                  ListTile(title: Text('item $index'))
                ]);
              } else {
                return ListTile(title: Text('item $index'));
              }
            }),
      ),
    );
  }
}

const String dateFormatter = 'MMMM dd, y';

extension DateHelper on DateTime {
  
   String formatDate() {
     final formatter = DateFormat(dateFormatter);
      return formatter.format(this);
  }
  bool isSameDate(DateTime other) {
    return this.year == other.year &&
        this.month == other.month &&
        this.day == other.day;
  }

  int getDifferenceInDaysWithNow() {
    final now = DateTime.now();
    return now.difference(this).inDays;
  }
}