ChildEventListener onChildAdded triggered prematurely in Android.

[sherwin de jesus]

Im trying to create a group chat application using Firebase.

On my onCreate, I have this:

chatMessageEditText = (EditText) findViewById(R.id.message);
chatMessageEditText.setOnEditorActionListener(new TextView.OnEditorActionListener() {
    @Override
    public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
        if (actionId==EditorInfo.IME_ACTION_SEND) {
            // Send new group chat message
            String key = fbChatRef.push().getKey();
            fbChatRef.child(key).child("sender_uid").setValue(fbUser.getUid());
            fbChatRef.child(key).child("sender_name").setValue(fbUser.getDisplayName());
            fbChatRef.child(key).child("timestamp").setValue( (new Date()).toString() );
            fbChatRef.child(key).child("message").setValue(v.getText().toString());

            v.setText("");

            return true;
        } else {
            return false;
        }
    }
});

Then on when user join a group, I have this:

// Listen to group chat
fbChatEventListener = new ChildEventListener() {
    @Override

    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            ChatMessage localChatMessage = new ChatMessage();
            localChatMessage.sender_name = dataSnapshot.child("sender_name").getValue().toString();
            localChatMessage.message_date = dataSnapshot.child("timestamp").getValue().toString();
            localChatMessage.message = dataSnapshot.child("message").getValue().toString();
            localChatMessage.sender_uid = dataSnapshot.child("sender_uid").getValue().toString();
            chatMessages.add(localChatMessage);

            chatMessageAdapter.notifyDataSetChanged();

            Log.d(TAG + "Chat:onChildAdded", "From:" + dataSnapshot.child("sender_name").getValue().toString() +
                    " " + dataSnapshot.child("timestamp").getValue().toString() +
                    "\n" + dataSnapshot.child("message").getValue().toString());
    }

    @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) {

    }
};
fbChatRef.orderByKey();
fbChatRef.addChildEventListener(fbChatEventListener);

First off, I have prevented the user to send a message without first joining a group.

When  setOnEditorActionListener is triggered, the dataSnapshot.child("sender_name") inside the onChildAdded is null when in fact, I have set it on setOnEditorActionListener. Thus I suspected that the onChildAdded is trigger prematurely.

Can somebody pls help me with this.

[Frank van Puffelen]

You're performing 4 separate write actions to the database:

            fbChatRef.child(key).child("sender_uid").setValue(fbUser.getUid());
            fbChatRef.child(key).child("sender_name").setValue(fbUser.getDisplayName());
            fbChatRef.child(key).child("timestamp").setValue( (new Date()).toString() );
            fbChatRef.child(key).child("message").setValue(v.getText().toString());

That first setValue() will already trigger the onChildAdded() method of your listener, which then tries to read a child property that doesn't exist yet:

         localChatMessage.sender_name = dataSnapshot.child("sender_name").getValue().toString();

The subsequent setValue() calls will trigger onChildChanged(), which your code is not handling.

The proper way to handle this is to write all the child properties of the message with a single setValue() operation

Our documentation on saving data on Android has some good examples of using a Java object to represent your data.

Since you already have a Java class for the ChatMessage, it could be as simple as:

    ChatMessage msg = new ChatMessage(fbUser.getUid(), fbUser.getDisplayName(), new Date()).toString(), v.getText().toString());

    fbChatRef.push().setValue(msg);

Now the entire write happens in one operation, so the onChildAdded() is triggered with the complete snapshot it expects.

    puf