随机选择子节点后如何在Firebase实时数据库中获取子节点的密钥

Question

我想获取Firebase实时数据库中子节点的key，也就是UID。我正在随机选择一个子节点，现在我想获取该子节点的密钥，以便对其进行进一步的操作。

databaseReferencePickers.addListenerForSingleValueEvent(new ValueEventListener() {
     @Override
     public void onDataChange(DataSnapshot dataSnapshot) {
         try {
            int pickerCount = (int) dataSnapshot.getChildrenCount();
            Random random = new Random();
            int rand = random.nextInt(pickerCount);
            Iterator itr = dataSnapshot.getChildren().iterator();

            for(int i = 0; i <= rand; i++) {
                itr.next();
            }

            pickerDetails = itr.next().toString();

            ObjectMapper oMapper = new ObjectMapper();
            map = oMapper.convertValue(itr.next(), Map.class);
            //pickerUID = Objects.requireNonNull(map.get("key")).toString();
            pickerUID = dataSnapshot.getKey();
            Toast.makeText(OrderPickupActivity.this,pickerUID,Toast.LENGTH_LONG).show();

         } catch (Exception e) {
              Toast.makeText(OrderPickupActivity.this, e.toString(), Toast.LENGTH_LONG).show();
         }
     }

     @Override
     public void onCancelled(DatabaseError databaseError) {

     }
});

你能帮帮我吗？每当我敬酒“PickerUID”的值时，我得到的值为 null。

Here is the image.

我想从选择器部分检索密钥。

Answer 1

如果您想通过在Pickers 节点上附加监听器来获得随机的uid，请使用以下代码行：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference pickersRef = rootRef.child("Pickers");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        List<String> uids = new ArrayList<>();
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String uid = ds.getKey();
            uids.add(uid);
        }

        String randomUid = new Random().nextInt(uids.size());
        //Do what you need to do with this random uid
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Log.d(TAG, "Error: ", task.getException()); //Don't ignore errors!
    }
};
pickersRef.addListenerForSingleValueEvent(valueEventListener);

看，您必须使用getChildren() 方法遍历DataSnapshot 对象才能获得结果。但是，这并不是最好的解决方案，因为您下载了整个 Pickers 节点，以获取单个随机 id。如需更感谢的解决方案，还请查看我在以下帖子中的回答：

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