Yes, the users have to supply their own media. The records are copyrighted. Most make their own mp3s from records they own. Music they are buying now come as mp3 files. The written part doesn't seem to have any restrictions, they are freely available from many places. I do the mp3 conversion for a few people but, only from records they own and they are the only person that gets it even if someone else wants the same recording. They do pay, through and organization, to play the music at commercial events. Probably some murky dark areas there.
This is aimed at a pretty small group of people using tablets. I don't think a phone would be a good platform, screen is just too small. I didn't know there were any modern devices with no external card. Is everything done from the web?
They simply have huge amounts of built-in memory and yes, external data is downloaded from somewhere....
Ah - your Project Designer has the GUI built in the phone template....
So in fact you could have everything comfortably on one Screen.
Makes life difficult! They may have their media on a MicroSD card, USB Stick, USB hard drive, A Cloud (Google Drive, Microsoft One, Amazon Free Tier, Drop Box etc), a website of their own. Perhaps direct access to commercial sites such as Spotify, Apple Music.
Your App cannot cater for every media source, so it must instead require the User to save/transfer their media to a standard Android folder, i.e. the music folder. Your App could create it's own folder inside the music folder.
Currently, there are not that many tablets using the most recent versions of Android, but it's best to design your file handling to the Android 11+ spec since everything will get to that level eventually (Android 12 released Oct 2021, Android 12L for Tablets later this year, Android 13 later this year).
So, to optimise the User experience and work with one list, all files should be stored in a single folder and all related files should have identical names except for their extension. So something like:
Concerto for Two Violins.mp3
Concerto for Two Violins.cue
Concerto for Two Violins.webp
Crazy Horses.mp3
Crazy Horses.cue
Crazy Horses.webp
The Message.mp3
The Message.cue
The Message.webp
The ListView will display only the file names (no extension) to the User and if selected, the App will load e.g. the three Crazy Horses files.
Yea every time I do a save as, it reverts back to the phone and I sometimes forget to change back to tablet if I'm not looking to change anything there.
The way it is right now it finds all mp3 files on the external storage, not just the ones in the music folder. I do transfer via USB but, I have found that the quickest way to transfer a lot of music is to take the card out and use a card reader. I'll probably have to teach many how to load their files into the right place anyway. Some of them are still toting 45's and a turntable around.
As of right now this works on Android 10 and 7.2, had to change permissions to be able to read html files on the 10. Sounds like Google is going to make that harder.
I did, your suggestion, successfully switch from list view to list picker. I think I like it better. Still have to add a search feature.
Some Tablet Specs:
Samsung Galaxy Tab A 10.1 (2019) 32GB (2/3GB Ram). [EU edition]. MicroSD Card; WiFi; USB-C; Bluetooth LE; Android 9
Samsung Galaxy Tab S5e 10.5 64/128GB (4/6GB Ram). MicroSD Card; WiFi; USB-3.1; Bluetooth LE; Android 9
Amazon Fire HD 10 (2019) 32/64GB (2GB Ram). MicroSD Card; WiFi; USB-C; Bluetooth LE; Android 9/Fire OS 7
Lenovo Tab M10 HD 10.1 (2020) 32/64GB (2/4GB Ram). MicroSD Card; WiFi; USB-C; Bluetooth LE; Android 10
Lenovo Yoga Tab 13 (2021). 256GB (8GB Ram). No Card Slot. WiFi; USB-C; Bluetooth LE; Android 11/12
That's doomed to disaster - not only because the User will have to hunt-and-peck everywhere, but also because that can only be done on the early Android platform. Android 11+ introduces Security measures that prevent whole device access by 3rd party Apps - your App is restricted to it's own folder (ASD [App Specific Directory]) and the Android standard public folders (i.e. Music in the case of your App).
Edit: not all mp3 files are music - some can be audio books and podcasts, so it pays to insist that the User puts music files in your App's music folder.
Sound quality freaks 
Here is the official list of sound formats supported by Android:
It includes the compressed, lossless FLAC format.
Not sure if the 'cue' would be a file for each music file but this is an example folder structure:
Since not every Tablet has a card slot, USB is the obvious choice for external storage/file transfer, but your App doesn't need to be involved with that, that's between the User and the OS 
If the PlayMusic folder is on the device and the device has 32GB of storage, that caters for a lot of music files. I expect your Users need higher quality 192Kbps mp3 files, average size about 5MB. So a thousand files is 5000MB or 5GB.
It's more like this, sorry, used the cue/instructions term interchangeably.
The method to get things on to a device is not terribly important at this point, I need to get it to work first. I'm trying to get small things accomplished before going on.
Right now I want to get two things to happen when one selection is made. Listen to something and look at something.
Many of them sound pretty crappy after being toted around for years. I for one have never seen the allure of those noisy records we had when kids.
I thought I had that sorted out but, it still finds everything on the card, no hunt and peck. All are on the list and can be used.
Not having any luck with getting rid of the file extension and just looking at the title. Right now I can do one or the other but it's two projects because of the extension.
...but not all are necessarily music files, hence the suggested folder structure.
I know that the instructions file is probably going to be an image. What does the cue consist of? Please give an accurate description of what it is for. Or are the instructions and the cue one and the same file?
I'm thinking that if this is text (cue and instructions), then an image is not the best choice.
Again, with known paths and file types, that's the easiest thing in the world.
Chris, thanks for your patience.
I think we both speak English but, aren't talking the same language. Cue/instruction are just a name I used, perhaps unwisely, for some sort of file that is visual, it is NOT the type of file. Such as jpg, html and pdf. You are right jpg is not the best choice. The file structure can be anything I make it on the storage device. Let's say it is something like this with the sound file being a mp3 and visual file a pdf. Or should all files, both pdf and mp3 be in the same folder?
What I have right now is it will find all mp3's that exist on the card, no matter where it is, and add it to the list. You can't use the name xxxx-xxxx because every device has a different name for the card, it might be xoxo-ooxx.
Maybe for you, not for me. I believe the problem may be here, I haven't found a way to search for all files in a specific path without using the file type.
DickB (seems I can't use my name)
They should be in their own folders. PDF is great format but:
- PDF Read takes the User out of your App
- Your App Users are not all going to be excellent at making PDFs.
I have seen that, but it isn't actually what is wanted in my opinion. Why not?
- Not every Tablet has a card slot, most especially the latest ones
- Not all MP3's are music
- It's one way to get the files onto the device - your App shouldn't limit the User to just this method!
Hi Richard
That search is all-encompassing, so it includes searching folders that do not contain the files you are searching for. With a known path, there is no search required, just load a file list of that folder (Play Music folder) and be confident that only the files intended are actually listed.
In this case it helps to read the documentation
You can filter by extension. To get a list of all files, use * as extension
Taifun