How It Works
Since iOS 8, Apple has implemented a way for storage services to integrate directly with the operating system for accessing files from a common interface. Today you can access all your favorite storage services using the Files app right from the home screen. All it takes is installing the storage provider's app and then enabling the service within the Files interface.
Enabling Storage Services
To get started, let's access the Files interface from inside of OnSong. To do this, locate the Songs button in the upper left corner of the Menubar and tap to open the Songs Menu. Make sure that you have the Songs tab selected and that you are viewing All Songs or a book. Tap on the + button in the lower right corner to access the Add Songs Menu and then tap on the Files option under the Import section. This will open the Files interface provided by the operating system.
Find the Locations area on the left side of the interface and look for the storage service you want to use. If you don't find it, you may need to enable it. To do so, tap on the Edit button in the navigation bar. This will reveal available storage services with switches, allowing you to enable the service you want to use. You can also change the order of the services as well. When finished, tap Done to save changes.
If you don't see the storage service that you want to use in this interface, make sure that you have the appropriate app installed and that the vendor supports the Files interface for accessing files.
Now tap on the storage service on the right to be displayed files on the right. This interface may varying depending on the storage service and how they have implemented their integration. You can tap on a file to import it into your library. Alternately, you can tap on the Select button in the navigation bar to select multiple files. When finished, tap on the Open button to import those files into your library.
We've prepared a video that demonstrates storage providers and the basic of how to import files from other storage services using the Files interface.
The appearance and name of the Files integration may change with different versions of iOS/iPadOS.