OnCreate.java

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

        mSendButton = (Button) findViewById(R.id.button_chat_send);
        mMessageEditText = (EditText) findViewById(R.id.edittext_chat);

        mRecyclerView = (RecyclerView) findViewById(R.id.reycler_chat);
        mLayoutManager = new LinearLayoutManager(this);
        mLayoutManager.setReverseLayout(true);
        mRecyclerView.setLayoutManager(mLayoutManager);

        OpenChannel.getChannel(mChannelUrl, new OpenChannel.OpenChannelGetHandler() {
            @Override
            public void onResult(final OpenChannel openChannel, SendBirdException e) {
                if (e != null) {
                    e.printStackTrace();
                    return;
                }

                openChannel.enter(new OpenChannel.OpenChannelEnterHandler() {
                    @Override
                    public void onResult(SendBirdException e) {
                        if (e != null) {
                            e.printStackTrace();
                            return;
                        };

                        mChatAdapter = new ChatAdapter(openChannel);
                        mRecyclerView.setAdapter(mChatAdapter);
                    }
                });
            }
        });

        mSendButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mChatAdapter.sendMessage(mMessageEditText.getText().toString());
                mMessageEditText.setText("");
            }
        });

        mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                if (mLayoutManager.findLastVisibleItemPosition() == mChatAdapter.getItemCount() - 1) {
                    mChatAdapter.loadPreviousMessages();
                }
            }
        });

    }