OnResume.java

  @Override
    protected void onResume() {
        super.onResume();

        // Receives messages from SendBird servers
        SendBird.addChannelHandler(CHANNEL_HANDLER_ID, new SendBird.ChannelHandler() {
            @Override
            public void onMessageReceived(BaseChannel baseChannel, BaseMessage baseMessage) {
                if (baseChannel.getUrl().equals(mChannelUrl) && baseMessage instanceof UserMessage) {
                    mChatAdapter.appendMessage((UserMessage) baseMessage);
                }
            }
        });
    }