How to sort/order a list by date in dart/flutter?

问题

I have the following list, that I am trying to re-order/ sort by the DateTime.

import 'package:intl/intl.dart'; 
//don't forget to add under dependencies pubspec.yml "intl: ^0.15.8"


List products = [];

//adding into the new list from raw API list
for(final item in rawProducts){

   var parsedDate = DateTime.parse.(item['expiryDate']);
   tmpArray = {
     'id': item['id'],
     'name': item['name'],
     'price': item['price'],
     'expiry': parsedDate
   }
   products.add(tmpArray);
  }
}


List products = [

 {id: 1242, name: milk, price: $5, expiry: 2019-11-25 00:00:00:000},
 {id: 1242, name: egg, price: $2, expiry: 2019-11-22 00:00:00:000},
 {id: 1243, name: bread, price: $3, expiry: 2019-11-22 00:00:00:000},
 {id: 1244, name: butter, price: $7, expiry: 2019-11-24 00:00:00:000},
 {id: 1247, name: butter, price: $7, expiry: 2019-11-23 00:00:00:000},

]

I would like to re-order the list in a way that the farthest expiry date shows up first:

 25-11-2019
 24-11-2019
 23-11-2019
 22-11-2019
 22-11-2019

What I have tried (updated) -> SOLVED by changing a.expiry into a['expiry'] :

  products.sort((a,b) {
    var adate = a['expiry'] //before -> var adate = a.expiry;
     var bdate = b['expiry'] //var bdate = b.expiry;
     return -adate.compareTo(bdate);
  });

on the sort function I am receiving this error (SOLVED by above fix):

Unhandled Exception: NoSuchMethodError: Class 
'_InternalLinkedHashMap<String, dynamic>'has no instance getter 'expiry'.

回答1:

In your example above, expiry is a String, not a DateTime object. You have a few options here, depending on what you want to achieve.

The easiest solution would be to use String's built in compareTo method, which allows sorting Strings. Those timestamps are already in a sortable format, so this would work:

products.sort((a,b) {
    return a.compareTo(b);
 });

Or more concise:

products.sort((a,b) => a.compareTo(b));

This is pretty basic. Like pskink mentioned in the comment, building on this you could convert the Strings to actual DateTime objects.

DateTime expiryAsDateTime = DateTime.parse(expiry);

DateTime also has a built in compareTo method, so the code snippet above would work with DateTimes as well as Strings.

If you want to reverse the order, just swap a and b.

回答2:

I fixed it by changing changing a.expiry into a['expiry'] and b.expiry into b['expiry']

products.sort((a,b) {
 var adate = a['expiry'] //before -> var adate = a.expiry;
 var bdate = b['expiry'] //before -> var bdate = b.expiry;
 return adate.compareTo(bdate); //to get the order other way just switch `adate & bdate`
});

回答3:

convert to DateTime

import 'package:intl/intl.dart';

void main() {
  List products = [
    "2019-11-25 00:00:00.000",
    "2019-11-22 00:00:00.000",
    "2019-11-22 00:00:00.000",
    "2019-11-24 00:00:00.000",
    "2019-11-23 00:00:00.000"
  ];
  List<DateTime> newProducts = [];
  DateFormat format = DateFormat("yyyy-MM-dd");

  for (int i = 0; i < 5; i++) {
    newProducts.add(format.parse(products[i]));
  }
  newProducts.sort((a,b) => a.compareTo(b));

  for (int i = 0; i < 5; i++) {
    print(newProducts[i]);
  }
}

without convert to DateTime

import 'package:intl/intl.dart';

void main() {
  List products = [
    "2019-11-25 00:00:00.000",
    "2019-11-22 00:00:00.000",
    "2019-11-22 00:00:00.000",
    "2019-11-24 00:00:00.000",
    "2019-11-23 00:00:00.000"
  ];

  products.sort((a,b) => a.compareTo(b));

  for (int i = 0; i < 5; i++) {
    print(products[i]);
  }
}

来源：https://stackoverflow.com/questions/57000166/how-to-sort-order-a-list-by-date-in-dart-flutter