Unable to call values from FirebaseDatabase Realtime Using FirebaseUI

问题

Above is just an example of the structure of the folder in FirebaseDatabase. My query is that how am I suppose to get those child node value.

Below is my code which I tried:

//FirebaseDatabase Collecting all the Item List
    ValueEventListener listener= new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            if (dataSnapshot.exists()){

                for (DataSnapshot ds: dataSnapshot.getChildren()){
                    arrayItemList.add(ds.getKey());
               }

                firebaseRecyclerViewItem(arrayItemList);
            }
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

            Log.i(TAG, "onCancelled: Unable to fetch data");

        }
    };
    lookUpDatabase.addValueEventListener(listener);

Here is code for the Method firebaseRecyclerViewItem():

public void firebaseRecyclerViewItem(final ArrayList<String> arrayItemList) {
    DatabaseReference reference = null;
    String referenceName = null;

    ValueEventListener valueEventListener = new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            //FirebaseDatabase 2'nd Reference Address
            for (DataSnapshot ds : dataSnapshot.getChildren()) {

                String key1 = ds.getKey();
                Log.i(TAG, "onDataChange: " + key1);

                String firebaseItemName = ds.child("DATA").getValue(String.class);
                Log.i(TAG, "onDataChange: " + firebaseItemName);
            }
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    };

    for (int i = 0; i < arrayItemList.size(); i++) {

        referenceName = arrayItemList.get(i);
        reference = FirebaseDatabase.getInstance().getReference().child("DATA").child(referenceName);
        reference.addValueEventListener(valueEventListener);

        //Loading RecyclerView
        RecyclerViewItemList(reference, referenceName);
    }

}

Is not that I am not able to get the values, I am able to get it however in the database pic which I have attached there are three FILE01, FILE02 and FILE03. I am only able to get the last FILE03, "01" value, I mean ValueEventListner skips all the other FILE present there only take the Last update or the last file. But I want all the files data present there to display it on my recyclerView.

I have also tried a different approached where I get the DataSnaphot, and use the for() Loop, where I used nested loop:

//FirebaseDatabase Collecting all the Item List
    ValueEventListener listener= new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            if (dataSnapshot.exists()){

                // here is where the changes which I have made, I tried to called the value which is impossible but still I tried to, but not result.

                for (DataSnapshot ds: dataSnapshot.getChildren()){

                   String key= ds.getKey();
                    String firebaseItemName = ds.child("DATA").getValue(String.class);
                Log.i(TAG, "onDataChange: " + firebaseItemName);

                }
            }
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

            Log.i(TAG, "onCancelled: Unable to fetch data");

        }
    };
    lookUpDatabase.addValueEventListener(listener);

    RecyclerViewItemList(lookUpDatabase);

Is there a way or a method which I can use to call the values.

回答1:

You should call notifyDataSetChanged() in for loop. Otherwise your reference and referenceName will be rewrited.

So your code should be

 for (int i = 0; i < arrayItemList.size(); i++){
//Add your data to arraylist

rvAdapter.notifyDataSetChanged();
}

Edit:

This will show your firebase data. I just changed your second method.

/*I changed Here*/
 private ArrayList<HashMap<String,String>> yourChildList = new ArrayList<>();

 ValueEventListener listener= new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

        if (dataSnapshot.exists()){


            for (DataSnapshot ds: dataSnapshot.getChildren()){

                /*I changed Here*/
                HashMap<String,String> dataMap = new HashMap<>();


               String key= ds.getKey();
                String firebaseItemName = ds.child("DATA").getValue(String.class);
            Log.i(TAG, "onDataChange: " + firebaseItemName);


            /*I changed Here*/
            dataMap.put(key,firebaseItemName);
            yourChildList.add(yourDataMap);

            }


            /*I changed Here
            *
            *I think this method is used to update data to your recyclerView
            *if I'm right, you can replace it
            *RecyclerViewItemList(lookUpDatabase);
            *
            */ 

            yourRecyclerAdapter = new RecyclerAdapter(yourChildList);
            yourRecyclerAdapter.notifyDataSetChanged();
            recyclerView.setAdapter(yourRecyclerAdapter);

        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.i(TAG, "onCancelled: Unable to fetch data");
    }
};
lookUpDatabase.addValueEventListener(listener);

Note:I don't recommend you to use nested listeners. You should avoid nested listener for better performance and maintainability. You should use Observer or LiveData to update Recyclerview.

来源：https://stackoverflow.com/questions/62099116/unable-to-call-values-from-firebasedatabase-realtime-using-firebaseui