@Override
 protected void onActivityResult(int requestCode, int resultCode, Intent data) {
   super.onActivityResult(requestCode, resultCode, data);
   if (resultCode == RESULT_OK) {
     if (requestCode == REQUEST_CODE_EMPTY_HISTORY) {
       EMChatManager.getInstance().clearConversation(toChatUsername);
     }
   }
 }
 @Override
 protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_chat);
   initialize();
 }