如何獲取Firebase中推送給孩子的最新數據？

Question

因此，我仍在嘗試使用我的應用程序並遇到另一堵磚牆，我想從已保存到Firebase的這組數據中檢索最新的“ bloodLevel”，並將其輸出到textview，但不確定如何去做：

"BGRatio" : "1",
  "CarbRatio" : "5",
  "Entries" : {
    "-KfcV3kfCMTcbeSa9Wv6" : {
      "BloodLevels" : "7.5",
      "Carbohydrates" : "20",
      "DateandTime" : "19 Mar 2017, 21:36:47",
      "Insulin" : "4.5"
    },
    "-KfcX05Fo2XDYLAkrBW-" : {
      "BloodLevels" : "14",
      "Carbohydrates" : "65",
      "DateandTime" : "19 Mar 2017, 21:45:17",
      "Insulin" : "20.0"
    },
    "-KfcrF6dKSolRl36dn4u" : {
      "BloodLevels" : "12",
      "Carbohydrates" : "90",
      "DateandTime" : "19 Mar 2017, 23:18:03",
      "Insulin" : "23.0"
    },
    "-Kfeqt1T27RKSNMkZrYA" : {
      "BloodLevels" : "24",
      "Carbohydrates" : "10000",
      "DateandTime" : "20 Mar 2017, 08:35:43",
      "Insulin" : "2017.0"
    },
    "-Kg4DU0eM8sx9uIHbDL4" : {
      "BloodLevels" : "13.3",
      "Carbohydrates" : "50",
      "DateandTime" : "Mar 25, 2017, 11:28:54 AM",
      "Insulin" : "16.3"
    },
    "-KgIxNJNSDpTAKpo62hn" : {
      "BloodLevels" : "8.0",
      "Carbohydrates" : "40",
      "DateandTime" : "Mar 28, 2017, 9:08:30 AM",
      "Insulin" : "9.0"
    },
    "-KgOJ-4eGU5z_dTuxfoq" : {
      "BloodLevels" : "10",
      "Carbohydrates" : "50",
      "DateandTime" : "Mar 29, 2017, 10:05:25 AM",
      "Insulin" : "13.0"
    }
  },
  "Ideal Level" : "7"
}

任何幫助，這將是巨大的，謝謝！！！

Answer 1

您應該將DateandTime保存為時間戳，以便可以在其上orderByChild('DateandTime') ，然后使用limitToLast(1)選擇最后一個。

https://firebase.google.com/docs/reference/android/com/google/firebase/database/Query.html#orderByChild(java.lang.String） https://firebase.google.com/docs/reference/ android / com / google / firebase / database / Query＃limitToLast（int）