add new features to my file manager android application

I have a file manager app. I need to add following features to it. 1. Request for sd card access, if not granted already, first time when user wants to perform a write operation on sd card files(delete,rename, move, copy etc) [login to view URL] files from one folder to another in internal storage, sd card and also move files from internal storage to sd card and vice versa Note: the project is being created on API 17 and I want to get it done using methods which does not require me to change API level of the project