How to retrieve value from the highest/last level node using 'ChildEventListener' from Firebase?

问题

I have several strings stored under specific reference: mReference.child(rID).child(userID2) which I want to retrieve using childEventListener as I am doing some task also when these string gets removed and that is only possible with onChildRemoved of ChildEventListener.

Here's what I have tried:

mReference.child(rID).child(userID2).addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                Log.d("dataHEre", dataSnapshot.getValue().toString());
            }
}

The problem is that I'm unable to retrieve data using keys here as dataHEre is logging out:

D/dataHEre: 28.8419556
D/dataHEre: 78.779063
D/dataHEre: 3
D/dataHEre: Railway Colony
D/dataHEre: Sleep
D/dataHEre: 12:36 AM
D/dataHEre: Superman

which are values?

So, I want to know how can I retrieve data here using keys and using ChildEventListener and then assign the data retrieved to various strings?

回答1:

I think that you are doing your query in the wrong way. onChildAdded method is retrieving you each child of a specific value (userID2 I suppose). If that is what you want, then just use a onValueEventListener() to retrieve the whole dataSnapshot of your userId2 node each time that it changes.

If you want to retrieve the data just once, you should use onSingleValueEventListener(). And OnChildEvent() is used to retrieve lists of data where you want to track each of the child individually. For example if you attach an OnChildEventListener to mReference.child(rID) you will get a OnChildAdded for each userId, what is pretty usefull like for example fill a RecyclerView or a ListView being able to update each item individually together with your Firebase Data.

If i'm not wrong what you want is just get updates of your userId2 reference, in that case attach a OnValueEventListener to that reference and you will get a call each time a value is modified, deleted, or added.

 firebaseDatabaseRef.addValueEventListener(new ValueEventListener() {
     @Override public void onDataChange(DataSnapshot dataSnapshot) {
        customPOJO customPOJO = dataSnapshot.getValue(YourCustomPOJO.class);
        customPOJO.getName();
        customPOJO.getEmail();
        customPOJO.getfavoriteFood();
        //and so on....

     }

     @Override public void onCancelled(DatabaseError databaseError) {

     }
  });

来源：https://stackoverflow.com/questions/41842681/how-to-retrieve-value-from-the-highest-last-level-node-using-childeventlistener