#Askfirebase Get the previous item values(POJO) in firebase recycler adapter in android

Question

AskFirebase How to get the previous item values(POJO) in firebase recycler adapter without using database query.

// Set up FirebaseRecyclerAdapter with the Query
    Query postsQuery = getQuery(mDatabase);
    mAdapter = new FirebaseRecyclerAdapter<Post, PostViewHolder>(Post.class, R.layout.item_post,
            PostViewHolder.class, postsQuery) {
        @Override
        protected void populateViewHolder(final PostViewHolder viewHolder, final Post model, final int position) {
            final DatabaseReference postRef = getRef(position);
            Log.e(TAG, "populateViewHolder: " + position);
            // Set click listener for the whole post view
            final String postKey = postRef.getKey();
            viewHolder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    // Launch PostDetailActivity
                    Intent intent = new Intent(getActivity(), PostDetailActivity.class);
                    intent.putExtra(PostDetailActivity.EXTRA_POST_KEY, postKey);
                    startActivity(intent);
                }
            });

            // Determine if the current user has liked this post and set UI accordingly
            if (model.stars.containsKey(getUid())) {

                viewHolder.starView.setImageResource(R.drawable.ic_toggle_star_24);
            } else {

                viewHolder.starView.setImageResource(R.drawable.ic_toggle_star_outline_24);
            }

            // Bind Post to ViewHolder, setting OnClickListener for the star button
            viewHolder.bindToPost(model, new View.OnClickListener() {
                @Override
                public void onClick(View starView) {
                    // Need to write to both places the post is stored
                    Log.e(TAG, "new: ");
                    DatabaseReference globalPostRef = mDatabase.child("posts").child(postRef.getKey());
                    DatabaseReference userPostRef = mDatabase.child("user-posts").child(model.uid).child(postRef.getKey());

                    // Run two transactions
                    onStarClicked(globalPostRef);
                    onStarClicked(userPostRef);
                }
            });
        }


    };

    mRecycler.setAdapter(mAdapter);

Suppose their are five cell list whenever i am facing second cell in the list that time i want to put a condition based on first cell value. So how i can fatch the value of first cell?

I already try to using arraylist to store the POJO of Post . But the problem is whenever some item is deleted from firebase table that item onDataChange call but populateViewHolder doesn't call. Their is also a way to get previous data using database query that is

DatabaseReference ref = getRef(position-1);
ref.addListenerForSingleValueEvent(new ValueEventListener() {

        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if (dataSnapshot.exists()) {
                        Log.e(TAG, "CHild exist: ");

                    } else {
                        Log.e(TAG, "no CHild exist: ");

                    }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    });

But i don't want to use this database query is their any other way?

Answer 1

The Design Firebase data structure for topic Answer and Comment its like your problem.

• gdtdg6765rf and hjgdhs567hd are unique key get by firebase
• hjgdhs567hd is answer
• gdtdg6765rf is comment to answer hjgdhs567hd
• created is -1*UNIX Timestamp for ordering
• date, time and toanswer was saved in comments by answer belong to
• if to delete answer set all flags "deleted=1" where child "toanswer=deleted answer key" to populate again

Answer 2

@eurosecom above image is my layout where their is a recycler view which populate through FirebaseRecyclerAdapter . Now those green cell is my single cell. you see a red circle which denote the date. in case of position==0 I just simple visible the layout, and in case of position>0 i want to put the condition based on previous item date.

Now in my FirebaseRecyclerAdapter i have to put the condition so i have to fetch the previous position date. So as i am already doing a network oparetion using Query to fetch the msg list i don't want to put addListenerForSingleValueEvent in the populateview again as because it will again fetch the val from database. So is their any other way to get the previous item?