Determine which storages (SD-Card) are available


I’m doing a eBook-Reader and want to give the user full possibillity where his eBooks are located.

tmplist.push({folder: {directory: Directory.Documents, path: ‘’}, label: ‘Internal Storage’});
tmplist.push({folder: {directory: Directory.External, path: ‘’}, label: ‘External’});
tmplist.push({folder: {directory: Directory.ExternalStorage, path: ‘’}, label: ‘SD-Card’});

Of course on an iPad those 3 Directories point to the same folder and on Android there might be SD-Card or not.

=> how to determine which are available? (and are different to each other)

Thank you very much!
grz, Clemens