如何在飞镖/颤振中按日期对列表进行排序/排序？ [英] How to sort/order a list by date in dart/flutter?

问题描述

我有以下列表，我想按DateTime重新排序/排序。

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},

]

我想以最远的到期日期重新排序列表首先显示：

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

我做什么尝试（更新）->通过将 a.expiry 更改为 a ['expiry'] 来解决：

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);
  });

关于排序功能，我收到此错误（由以上修复解决）：

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'.

推荐答案

在上面的示例中，到期时间是 String ，而不是DateTime对象。

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.

最简单的解决方案是使用String内置的 compareTo 方法，该方法可以进行排序字符串。这些时间戳已经是可排序的格式，因此可以使用：

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);
 });

或更简洁：

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

这是非常基本的。就像注释中提到的pskink一样，可以在此基础上将字符串转换为实际的DateTime对象。

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 也具有内置的 compareTo 方法，因此上面的代码段将与DateTimes以及Strings一起使用。

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

如果要反转顺序，只需交换 a 和 b 。

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

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