setControlChannelCallback method
Implementation
void setControlChannelCallback(String channelName, Function callback) {
Map<String, String> map =
generateMessage(MessageType.SET_CONTROL_CHANNEL_CALLBACK, content: "");
map[MessageTag.CHANNEL_NAME] = channelName;
_callbackList.add(callback);
map[MessageTag.CALLBACK_INDEX] = _callbackList.length.toString();
_sendPort.send([map, _callbackPort.sendPort]);
}