How to show single progress for multiple files downloads?.

You need to handle it by yourself like : 
- Keep track of all files currently downloaded
- Create an object with the state of all these download status
- Create methods to read global status (getGlobalPercent()).

You have to calculate the percent of each download to determine the global percent :( percent1 + percent 2 + percent 3 + percent n) / n

If each download has a different size, you have to calculate it like : 
100 / totalSizeOfAllFiles * (size1 + size2 + sizeN)