Flutter按时间戳对Firebase快照进行排序 [英] Flutter sort Firebase snapshot by timestamp

问题描述

我正在尝试按时间戳对快照进行排序，但返回原始顺序.
数据结构看起来像这样

I'm trying to sort snapshot by timestamp but returns original order.
data structure looks like this

我有两个快照，时间戳记分别是-1536025466539和-1536025893015.
因此，我希望-1536025893015在排序后排在第一位. 有人知道如何正确排序吗?

I have two snapshot and timestamps are -1536025466539 and -1536025893015.
So, I expect -1536025893015 to come first after sorted. Does anyone know how to sort correctly?

代码:

Map<dynamic, dynamic> map = snapshot.data?.snapshot?.value;
    map.values.toList().sort((a, b) {
      return a['timestamp'].compareTo(b['timestamp']);
    // also not work return b['timestamp'].compareTo(a['timestamp']);
  });

推荐答案

从上面的代码看来，您没有variable来保存列表.

From the above code, it looks like you are not having a variable to hold the list.

 Map<dynamic, dynamic> map = {
    "one": {"timestamp": 1},
    "two": {"timestamp": 2}
  };
  List list = map.values.toList(); //variable which holds new list created from Map.
                                   //As it new list, any change in list will not have no impact on map.
  list.sort((a, b) {
    return b["timestamp"].compareTo(a["timestamp"]);
  }); // inplace sort
  print(list); // [{timestamp: 2}, {timestamp: 1}]

如果您还要在结果中显示key，

If you want key also in the result,

 var list = map.entries.toList();
 list.sort((a, b) => b.value["timestamp"].compareTo(a.value["timestamp"]));
 var list2 = list.map((a) => {a.key: a.value}).toList();
 print(list2); // [{two: {timestamp: 2}}, {one: {timestamp: 1}}]

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