Android Question How to retrieve a file from memory card or usb flash

Hello,
I am on the mobile so my reply will be short. I am sorry for that.

You should take a look at the Files set of instruction : http://www.b4x.com/android/help/files.html#file
Your USB or SD card is under File.DirRootExternal. To create the necessary file's path, take a look at the File.Combine method.

And of course, you could check if the SD card is readable using File.ExternalReadable

Hope this would help you to find the right way