Flutter 按时间戳对 Firebase 快照进行排序

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

我有两个快照，时间戳是-1536025466539 and -1536025893015.
所以，我期望-1536025893015排序后排在第一位。 有谁知道如何正确排序？

Code:

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']);
  });

从上面的代码来看，您似乎没有variable保存清单。

 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}]

如果你想key也在结果中，

 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}}]