How to enable user to delete only specific data from Firebase Realtime Database

Question

I am trying to delete messages between users in Firebase Realtime Database.I am successfully able to delete the messages but i want to add a condition that the user can't delete messages he received and only be able to delete messages that he sent, currently user is able to delete messages he received as well as those he sent from the firebase realtime database.

My code

MessageActivity.java

    public class MessageActivity extends AppCompatActivity {
    CircleImageView profile_image;
    TextView user_name;

    FirebaseFirestore fstore;
    FirebaseAuth fAuth;
    FirebaseUser fuser;
    DatabaseReference reference;


    Toolbar toolbar;
    ImageButton imageButton;
    EditText textsend;
    String userID;

    MessageAdapter messageAdapter;
    List<Chat> mChat;
    RecyclerView recyclerView;

    DatabaseReference Chatreference;

    String TAG = "MyTag";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_message);

        fAuth = FirebaseAuth.getInstance();
        fstore = FirebaseFirestore.getInstance();
        userID = fAuth.getCurrentUser().getUid();


        profile_image = findViewById(R.id.profile_image);
        user_name = findViewById(R.id.username);
        imageButton = findViewById(R.id.btn_send);
        textsend = findViewById(R.id.text_send);

        recyclerView = findViewById(R.id.recycler_view2);
        recyclerView.setHasFixedSize(true);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getApplicationContext());
        linearLayoutManager.setStackFromEnd(true);
        recyclerView.setLayoutManager(linearLayoutManager);

        toolbar = findViewById(R.id.myToolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("");
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                finish();
            }
        });

        Intent intent = getIntent();
        String userid = intent.getStringExtra("userid");

        fuser = FirebaseAuth.getInstance().getCurrentUser();
        //String username = intent.getStringExtra("UserName");
        User user=new User();



        reference = FirebaseDatabase.getInstance().getReference("Users").child(userid);

        reference.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                User user = dataSnapshot.getValue(User.class);
                user_name.setText(user.getFirst());
                Log.d(TAG, "Single Event Listener called");

                if (user.getImageURL().equals("default")) {
                    profile_image.setImageResource(R.mipmap.ic_launcher);
                } else {
                    //and this
                    Glide.with(getApplicationContext()).load(user.getImageURL()).into(profile_image);
                }


                readMessages(fuser.getUid(), userid, user.getImageURL());

            }

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

            }
        });




        imageButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String msg = textsend.getText().toString();
                textsend.setText("");
                if (!msg.equals("")) {
                    sendMessage(fuser.getUid(), userid, msg);
                } else {
                    Toast.makeText(MessageActivity.this, "Empty messages cant be send", Toast.LENGTH_SHORT).show();
                }
            }
        });

    }

    @Override
    protected void onStart() {
        super.onStart();
        User user=new User();

        //readMessages(fuser.getUid(), userid, user.getImageURL());
    }

    private void sendMessage(String sender, final String receiver, String message) {

        HashMap<String, Object> hashMap = new HashMap<>();
        hashMap.put("sender", sender);
        hashMap.put("receiver", receiver);
        hashMap.put("message", message);


        DatabaseReference Chatreference = FirebaseDatabase.getInstance().getReference("Chats");

        String key = Chatreference.push().getKey();
        Chatreference.child(key).setValue(hashMap);


    }

    private void readMessages(String myid, String userid, String imageurl) {

        mChat = new ArrayList<>();

        Chatreference = FirebaseDatabase.getInstance().getReference("Chats");


        Chatreference.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                Chat chat = dataSnapshot.getValue(Chat.class);
                if (chat.getReceiver().equals(myid) && chat.getSender().equals(userid) ||
                        chat.getReceiver().equals(userid) && chat.getSender().equals(myid)) {
                    chat.setMessageId(dataSnapshot.getKey());
                    mChat.add(chat);
                    Log.d(TAG, "Child_Event_Listener_Called");
                    Log.d(TAG, "msg " + chat.getMessage());
                }

                messageAdapter = new MessageAdapter(MessageActivity.this, mChat, imageurl);
                recyclerView.setAdapter(messageAdapter);
                messageAdapter.notifyDataSetChanged();


            }


            @Override
            public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {


            }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

                Chat chat = dataSnapshot.getValue(Chat.class);
                chat.setMessageId(dataSnapshot.getKey());

                mChat.remove(chat);
                messageAdapter.notifyDataSetChanged();


            }

            @Override
            public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            }

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

            }

        });





    }

}

MessageAdapter.java

    public class MessageAdapter extends RecyclerView.Adapter<MessageAdapter.ViewHolder> {

    public static  final int MSG_TYPE_LEFT = 0;
    public static  final int MSG_TYPE_RIGHT = 1;

    private Context mContext;
    private List<Chat> mChat;
    String imageurl;

    FirebaseUser fuser;

    public MessageAdapter(Context mContext, List<Chat> mChat,String imageurl) {
        this.mContext = mContext;
        this.mChat = mChat;
        this.imageurl=imageurl;

    }

    @NonNull
    @Override
    public MessageAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        if (viewType == MSG_TYPE_RIGHT) {
            View view = LayoutInflater.from(mContext).inflate(R.layout.chat_item_right, parent, false);

            return new MessageAdapter.ViewHolder(view);
        }
        else {
            View view = LayoutInflater.from(mContext).inflate(R.layout.chat_item_left, parent, false);

            return new MessageAdapter.ViewHolder(view);

        }
    }

    @Override
    public void onBindViewHolder(@NonNull MessageAdapter.ViewHolder holder, int position) {

        Chat chat=mChat.get(position);
        holder.show_message.setText(chat.getMessage());

        if (imageurl.equals("default")){
            holder.profile_image.setImageResource(R.mipmap.ic_launcher);
        } else {
            Glide.with(mContext).load(imageurl).into(holder.profile_image);
        }

        holder.show_message.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View v) {

                String message_id=chat.getMessageId();
                Task<Void> task = Utils.removeUser(message_id);
                task.addOnSuccessListener(new OnSuccessListener<Void>() {
                    @Override
                    public void onSuccess(Void aVoid) {
                        Toast.makeText(mContext,"Message Deleted",Toast.LENGTH_SHORT).show();
                    }
                });


                return true;
            }
        });


    }

    @Override
    public int getItemCount() {
        return mChat.size();
        }
    public class ViewHolder extends RecyclerView.ViewHolder{

         public TextView show_message;
         public ImageView profile_image;

        public ViewHolder(@NonNull View itemView) {
        super(itemView);
        show_message=itemView.findViewById(R.id.show_message);
        profile_image=itemView.findViewById(R.id.profile_image);

        }
    }

    @Override
    public int getItemViewType(int position) {
        fuser= FirebaseAuth.getInstance().getCurrentUser();
        if (mChat.get(position).getSender().equals(fuser.getUid())){
            return MSG_TYPE_RIGHT;
        }
        else {
            return MSG_TYPE_LEFT;
        }
    }
}

Chat.java

    public class Chat {
    private String sender;
    private String receiver;
    private  String message;
    String MessageId;

    public Chat(String sender, String receiver, String message) {
        this.sender = sender;
        this.receiver = receiver;
        this.message = message;
    }

    public Chat() {
    }

    public String getSender() {
        return sender;
    }

    public void setSender(String sender) {
        this.sender = sender;
    }

    public String getReceiver() {
        return receiver;
    }

    public void setReceiver(String receiver) {
        this.receiver = receiver;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public String getMessageId() {
        return MessageId;
    }

    public void setMessageId(String messageId) {
        MessageId = messageId;
    }

    @Override
    public boolean equals(@Nullable Object obj) {
        if(obj instanceof Chat){
            Chat chat=(Chat) obj;
            return this.MessageId.equals(chat.getMessageId());}
        else
            return false;
    }
}

Answer 1

Base on your Chat object you have sender and receiver Ids. So you can do the following inside onBindViewHolder

if (chat.getSender().equals(fuser.getUid())){
      // enable/show delete button 
}
 else{
      // disable/hide delete button 
}