About untity send messages with android?

at androiod send a message to untiy need to extend UnityPlayerActivity to use UnityPlayer.UnitySendMessage send a message, but the activity is an interface, I need to make untiy download some data in order to properly display interface, but the download process is relatively long, and I do not want to let the user to wait so I hope to start UnityPlayerActivity before starting untiy, android send a message to untiy start downloading data, the download is complete, send a message to android, you can ask to do this?