How to delete messages from firebase Database?

Question

I am working on a chat application connected to firebase. I am trying to add a future where I can delete a message. This is what I have tried but it's not working.

This is the code

...package com.sollie.ian.eunice.ui


public class ChatActivity extends AppCompatActivity  {
    private RecyclerView recyclerChat;
    public static final int VIEW_TYPE_USER_MESSAGE = 0;
    public static final int VIEW_TYPE_FRIEND_MESSAGE = 1;
    private ListMessageAdapter adapter;
    public String roomId;
    private ArrayList<CharSequence> idFriend;
    private Consersation consersation;
    private MessageInput editWriteMessage;
    private LinearLayoutManager linearLayoutManager;
    public static HashMap<String, Bitmap> bitmapAvataFriend;
    public Bitmap bitmapAvataUser;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chat);
        Intent intentData = getIntent();
        idFriend = intentData.getCharSequenceArrayListExtra(StaticConfig.INTENT_KEY_CHAT_ID);
        roomId = intentData.getStringExtra(StaticConfig.INTENT_KEY_CHAT_ROOM_ID);
        String nameFriend = intentData.getStringExtra(StaticConfig.INTENT_KEY_CHAT_FRIEND);

        consersation = new Consersation();


        String base64AvataUser = SharedPreferenceHelper.getInstance(this).getUserInfo().avata;
        if (!base64AvataUser.equals(StaticConfig.STR_DEFAULT_BASE64)) {
            byte[] decodedString = Base64.decode(base64AvataUser, Base64.DEFAULT);
            bitmapAvataUser = BitmapFactory.decodeByteArray(decodedString, 0, decodedString.length);
        } else {
            bitmapAvataUser = null;
        }

        editWriteMessage =  findViewById(R.id.input);
        if (idFriend != null && nameFriend != null) {
            getSupportActionBar().setTitle(nameFriend);
            linearLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
            recyclerChat =  findViewById(R.id.recyclerChat);
            recyclerChat.setLayoutManager(linearLayoutManager);
            adapter = new ListMessageAdapter(this, consersation, bitmapAvataFriend, bitmapAvataUser);
            FirebaseDatabase.getInstance().getReference().child("message/" + roomId).addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                    if (dataSnapshot.getValue() != null) {
                        HashMap mapMessage = (HashMap) dataSnapshot.getValue();
                        Message newMessage = new Message();
                        newMessage.idSender = (String) mapMessage.get("idSender");
                        newMessage.idReceiver = (String) mapMessage.get("idReceiver");
                        newMessage.text = (String) mapMessage.get("text");
                        newMessage.timestamp = (long) mapMessage.get("timestamp");
                        consersation.getListMessageData().add(newMessage);
                        adapter.notifyDataSetChanged();
                        linearLayoutManager.scrollToPosition(consersation.getListMessageData().size() - 1);
                    }
                }

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

                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {

                }

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

                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });
            recyclerChat.setAdapter(adapter);
        }



        editWriteMessage.setInputListener(input -> {
            String content = input.toString().trim();
            if (content.length() > 0) {
                //  editWriteMessage.setTex("");
                Message newMessage = new Message();
                newMessage.text = content;
                newMessage.idSender = StaticConfig.UID;
                newMessage.idReceiver = roomId;
                newMessage.timestamp = System.currentTimeMillis();
                FirebaseDatabase.getInstance().getReference().child("message/" + roomId).push().setValue(newMessage);
            }
            return  true;
        });
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if(item.getItemId() == android.R.id.home){
            Intent result = new Intent();
            result.putExtra("idFriend", idFriend.get(0));
            setResult(RESULT_OK, result);
            this.finish();
        }
        return true;
    }

    @Override
    public void onBackPressed() {
        Intent result = new Intent();
        result.putExtra("idFriend", idFriend.get(0));
        setResult(RESULT_OK, result);
        this.finish();
    }
}

class ListMessageAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private Context context;
    private Consersation consersation;
    private HashMap<String, Bitmap> bitmapAvata;
    private HashMap<String, DatabaseReference> bitmapAvataDB;
    private Bitmap bitmapAvataUser;
    private String roomId;

    public ListMessageAdapter(Context context, Consersation consersation, HashMap<String, Bitmap> bitmapAvata, Bitmap bitmapAvataUser) {
        this.context = context;
        this.consersation = consersation;
        this.bitmapAvata = bitmapAvata;
        this.bitmapAvataUser = bitmapAvataUser;
        bitmapAvataDB = new HashMap<>();
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (viewType == ChatActivity.VIEW_TYPE_FRIEND_MESSAGE) {
            View view = LayoutInflater.from(context).inflate(R.layout.rc_item_message_friend, parent, false);
            return new ItemMessageFriendHolder(view);
        } else if (viewType == ChatActivity.VIEW_TYPE_USER_MESSAGE) {
            View view = LayoutInflater.from(context).inflate(R.layout.rc_item_message_user, parent, false);
            return new ItemMessageUserHolder(view);
        }
        return null;
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (holder instanceof ItemMessageFriendHolder) {
            ((ItemMessageFriendHolder) holder).txtContent.setText(consersation.getListMessageData().get(position).text);
            Bitmap currentAvata = bitmapAvata.get(consersation.getListMessageData().get(position).idSender);
            if (currentAvata != null) {
                ((ItemMessageFriendHolder) holder).avata.setImageBitmap(currentAvata);
            } else {
                final String id = consersation.getListMessageData().get(position).idSender;
                if(bitmapAvataDB.get(id) == null){
                    bitmapAvataDB.put(id, FirebaseDatabase.getInstance().getReference().child("user/" + id + "/avata"));
                    bitmapAvataDB.get(id).addListenerForSingleValueEvent(new ValueEventListener() {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot) {
                            if (dataSnapshot.getValue() != null) {
                                String avataStr = (String) dataSnapshot.getValue();
                                if(!avataStr.equals(StaticConfig.STR_DEFAULT_BASE64)) {
                                    byte[] decodedString = Base64.decode(avataStr, Base64.DEFAULT);
                                    ChatActivity.bitmapAvataFriend.put(id, BitmapFactory.decodeByteArray(decodedString, 0, decodedString.length));
                                }else{
                                    ChatActivity.bitmapAvataFriend.put(id, BitmapFactory.decodeResource(context.getResources(), R.drawable.default_avata));
                                }
                                notifyDataSetChanged();
                            }
                        }

                        @Override
                        public void onCancelled(DatabaseError databaseError) {

                        }
                    });
                }
            }
        } else if (holder instanceof ItemMessageUserHolder) {
            ((ItemMessageUserHolder) holder).txtContent.setText(consersation.getListMessageData().get(position).text);
            if (bitmapAvataUser != null) {
                ((ItemMessageUserHolder) holder).avata.setImageBitmap(bitmapAvataUser);
            }
            ((ItemMessageUserHolder) holder).txtContent.setOnLongClickListener(new View.OnLongClickListener() {
                @Override
                public boolean onLongClick(View v) {
                    AlertDialog.Builder builder = new AlertDialog.Builder(context);
                    builder.setTitle("Delete Message");
                    builder.setMessage("Are You Sure To Delete This Messgae");
                    builder.setPositiveButton("Delete", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            deleteMsg(position);
                        }


                    });
                    builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            dialog.dismiss();
                        }
                    });
                    builder.create().show();
                    return false;
                }
            });

        }

    }

    private void deleteMsg(int position) {

        final String myuid = FirebaseAuth.getInstance().getCurrentUser().getUid();
        String msgtimestmp =String.valueOf(consersation.getListMessageData().get(position).timestamp);
        String message=consersation.getListMessageData().get(position).text;

         DatabaseReference roofRef=FirebaseDatabase.getInstance().getReference();
         roofRef.child("message").child(message)
                 .removeValue().addOnCompleteListener(new OnCompleteListener<Void>() {
             @Override
             public void onComplete(@NonNull Task<Void> task) {
                if(task.isSuccessful())
                {
                    Toast.makeText(context, "deleted", Toast.LENGTH_SHORT).show();
                }else
                {
                    Toast.makeText(context, "failed", Toast.LENGTH_SHORT).show();
                }
             }
         });
    }

    @Override
    public int getItemViewType(int position) {
        return consersation.getListMessageData().get(position).idSender.equals(StaticConfig.UID) ? ChatActivity.VIEW_TYPE_USER_MESSAGE : ChatActivity.VIEW_TYPE_FRIEND_MESSAGE;
    }

    @Override
    public int getItemCount() {
        return consersation.getListMessageData().size();
    }
}

class ItemMessageUserHolder extends RecyclerView.ViewHolder {
    public TextView txtContent;
    public CircleImageView avata;

        public ItemMessageUserHolder(View itemView) {
            super(itemView);
            txtContent =  itemView.findViewById(R.id.textContentUser);
            avata =  itemView.findViewById(R.id.imageView2);
        }
    
    
    }

class ItemMessageFriendHolder extends RecyclerView.ViewHolder {
    public TextView txtContent;
    public CircleImageView avata;

    public ItemMessageFriendHolder(View itemView) {
        super(itemView);
        txtContent =  itemView.findViewById(R.id.textContentFriend);
        avata =  itemView.findViewById(R.id.imageView3);
    }
}

And this is what I have tried

private void deleteMsg(int position) {
    final String myuid = FirebaseAuth.getInstance().getCurrentUser().getUid();
    String msgtimestmp =String.valueOf(consersation.getListMessageData().get(position).timestamp);
    String message=consersation.getListMessageData().get(position).text;

     DatabaseReference roofRef=FirebaseDatabase.getInstance().getReference();
     roofRef.child("message").child(message)
             .removeValue().addOnCompleteListener(new OnCompleteListener<Void>() {
         @Override
         public void onComplete(@NonNull Task<Void> task) {
            if(task.isSuccessful())
            {
                Toast.makeText(context, "deleted", Toast.LENGTH_SHORT).show();
            }else
            {
                Toast.makeText(context, "failed", Toast.LENGTH_SHORT).show();
            }
         }
     });
}

What am I doing wrong?

Answer 1

The problem is here:

String message=consersation.getListMessageData().get(position).text;

DatabaseReference roofRef=FirebaseDatabase.getInstance().getReference();
roofRef.child("message").child(message).removeValue()

You're trying to delete the message based on its text , but to delete a node from Firebase you need to know its key .

This means that when you read the messages from the database, you'll need to store dataSnapshot.getKey() for each message (probably as a field in your Message class). Then when you are ready to delete the message, you can get the key from that class and pass it into the database call, with something like:

String key= consersation.getListMessageData().get(position).key; // 👈 

DatabaseReference roofRef=FirebaseDatabase.getInstance().getReference();
roofRef.child("message").child(key).removeValue()... // 👈