通過日期戳記對Firebase數據進行排序

Question

Ia正在開發一個應用程序，該應用程序以"yyyy/MM/dd kk:mm:ss"的格式接收datamessages和timestamp。這裏是JSON數據格式。

"NOT20170828132901" : 
{ 
      "code" : "Your order status has been updated to Rejected", 
      "date" : "2017/08/28 13:29:01", 
      "title" : "Order update SPB20170825095233542" 
} 

我想排序基於最新時間戳NOTNUMBER。我試着用limitToLast(i)，還有limitToFirst(i)，但是是靜靜的。結果是升序。 Iwant將日期戳分類爲降序。我也嘗試使用startAt(futuredatestamp).endAt(pastdatestamp)，但不工作。我想在此排序：

"NOT20170828140827" : { 
      "code" : "Your order status has been updated to Rejected", 
      "date" : "2017/08/28 14:08:27", 
      "title" : "Order update SPB20170825095233542" 
     }, 
     "NOT20170828140436" : { 
      "code" : "Your order status has been updated to Delivered", 
      "date" : "2017/08/28 14:04:36", 
      "title" : "Order update SPB20170825095233542" 
     }, 
     "NOT20170828132901" : { 
      "code" : "Your order status has been updated to Rejected", 
      "date" : "2017/08/28 13:29:01", 
      "title" : "Order update SPB20170825095233542" 
     }, 
     "NOT20170828115852" : { 
      "code" : "Your order status has been updated to Rejected", 
      "date" : "2017/08/28 11:58:52", 
      "title" : "Order update SPB20170825095233542" 
     }, 
     "NOT20170828014147" : { 
      "code" : "Your order status has been updated to IN TRANSIT", 
      "date" : "2017-08-28 01:41:47", 
      "title" : "Order update : SPB20170825095233542" 
     } 

使用過濾器參數時有些困惑。

請幫幫我。在此先感謝

Answer 1

保存日期和時間在火力地堡數據庫最好的做法，就是用ServerValue.TIMESTAMP像這樣把它保存爲TIMESTAMP：

DatabaseReference ref = FirebaseDatabase.getInstance().getReference(); 
Map map = new HashMap(); 
map.put("time", ServerValue.TIMESTAMP); 
yourRef.child("yourNode").updateChildren(map); 

記住，你保存TIMESTAMP作爲Map但你檢索它作爲long。爲了取回數據，我建議你使用這種方法：

public static String getTimeDate(long timeStamp){ 
    try{ 
     DateFormat dateFormat = getDateTimeInstance(); 
     Date netDate = (new Date(timeStamp)); 
     return dateFormat.format(netDate); 
    } catch(Exception e) { 
     return "date"; 
    } 
} 

然後在查詢中orderBy()方法將肯定工作。

Answer 2

假設您在Recyclerview中顯示來自Firebase的數據，請添加此代碼。

mLayoutManager = new LinearLayoutManager(MyActivity.this); 
mLayoutManager.setReverseLayout(true); 
mLayoutManager.setStackFromEnd(true); 

mRecyclerView.setLayoutManager(mLayoutManager); 
mRecyclerView.setAdapter(yourAdapter); 

上面的代碼做了什麼，它顛倒了recyclerview的內容。