节点的第一个条目为空

Question

curl -X PUT -d '{ "1": { "name": "Hauptbahnhof Berlin", "city": "Berlin"}, "2": { "name": "Hackerscher Markt", "city": "Berlin"}, "3": { "name": "Hauptbahnhof Frankfurt", "city": "Frankfurt"} }' 'https://xxx.firebaseio.com/stations.json'

结果

看起来像导出：

{
  "stations" : [ null, {
    "city" : "Berlin",
    "name" : "Hauptbahnhof Berlin"
  }, {
    "city" : "Berlin",
    "name" : "Hackerscher Markt"
  }, {
    "city" : "Frankfurt",
    "name" : "Hauptbahnhof Frankfurt"
  } ]
}

现在选择数据的值为空，为什么会这样呢？

FirebaseDatabase database = FirebaseDatabase.getInstance();
        DatabaseReference stationsRef = database.getReference("stations");
        stationsRef.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                ArrayList<Map<String, String>> value = (ArrayList<Map<String, String>>) dataSnapshot.getValue();
                Log.d(TAG, "Value is: " + value.toString());
            }

            @Override
            public void onCancelled(DatabaseError error) {
                // Failed to read value
                Log.w(TAG, "Failed to read value.", error.toException());
            }
        });

  

=＆GT;价值是：[null，{name = Hauptbahnhof Berlin，city = Berlin}，{name = Hackerscher Markt，city = Berlin}，{name = Hauptbahnhof Frankfurt，   城市=法兰克福}]

Answer 1

如果未传递，Firebase会自动将索引0添加为空值。所以将插入更改为

curl -X PUT -d '{ "0": { "name": "Hauptbahnhof Berlin", "city": "Berlin"}, "1": { "name": "Hackerscher Markt", "city": "Berlin"}, "2": { "name": "Hauptbahnhof Frankfurt", "city": "Frankfurt"} }' 'https://xxx.firebaseio.com/stations.json'

解决了这个问题。