app/src/main/java/com/firebase/uidemo/database/firestore/FirestoreChatActivity.java [75:118]:
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        ImeHelper.setImeOnDoneListener(mBinding.messageEdit, () -> onSendClick());

        mBinding.sendButton.setOnClickListener(view -> onSendClick());
    }

    @Override
    public void onStart() {
        super.onStart();
        if (isSignedIn()) {
            attachRecyclerViewAdapter();
        }
        FirebaseAuth.getInstance().addAuthStateListener(this);
    }

    @Override
    protected void onStop() {
        super.onStop();
        FirebaseAuth.getInstance().removeAuthStateListener(this);
    }

    @Override
    public void onAuthStateChanged(@NonNull FirebaseAuth auth) {
        mBinding.sendButton.setEnabled(isSignedIn());
        mBinding.messageEdit.setEnabled(isSignedIn());

        if (isSignedIn()) {
            attachRecyclerViewAdapter();
        } else {
            Toast.makeText(this, R.string.signing_in, Toast.LENGTH_SHORT).show();
            auth.signInAnonymously().addOnCompleteListener(new SignInResultNotifier(this));
        }
    }

    private boolean isSignedIn() {
        return FirebaseAuth.getInstance().getCurrentUser() != null;
    }

    private void attachRecyclerViewAdapter() {
        final RecyclerView.Adapter adapter = newAdapter();

        // Scroll to bottom on new messages
        adapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
            @Override
            public void onItemRangeInserted(int positionStart, int itemCount) {
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app/src/main/java/com/firebase/uidemo/database/realtime/RealtimeDbChatActivity.java [61:104]:
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        ImeHelper.setImeOnDoneListener(mBinding.messageEdit, () -> onSendClick());

        mBinding.sendButton.setOnClickListener(view -> onSendClick());
    }

    @Override
    public void onStart() {
        super.onStart();
        if (isSignedIn()) {
            attachRecyclerViewAdapter();
        }
        FirebaseAuth.getInstance().addAuthStateListener(this);
    }

    @Override
    protected void onStop() {
        super.onStop();
        FirebaseAuth.getInstance().removeAuthStateListener(this);
    }

    @Override
    public void onAuthStateChanged(@NonNull FirebaseAuth auth) {
        mBinding.sendButton.setEnabled(isSignedIn());
        mBinding.messageEdit.setEnabled(isSignedIn());

        if (isSignedIn()) {
            attachRecyclerViewAdapter();
        } else {
            Toast.makeText(this, R.string.signing_in, Toast.LENGTH_SHORT).show();
            auth.signInAnonymously().addOnCompleteListener(new SignInResultNotifier(this));
        }
    }

    private boolean isSignedIn() {
        return FirebaseAuth.getInstance().getCurrentUser() != null;
    }

    private void attachRecyclerViewAdapter() {
        final RecyclerView.Adapter adapter = newAdapter();

        // Scroll to bottom on new messages
        adapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
            @Override
            public void onItemRangeInserted(int positionStart, int itemCount) {
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