Android app: Give to user the owning of model files by keeping them in `/sdcard/` subdirectory

[mnba]

Suggestion: give to user functionality of owning model files by himself, by means of
moving the storage of model files to user accessible place in Android within subdirectory of
/sdcard/.
Particularly the directory with MNN app models in Android system can be called
/sdcard/mnn-models .
.
I believe this is good suggestion, which only such unique open source app could give to user:
thus becoming not only open source app but also open data app.

Advantages

• User can remove extra files by himself, this is related to Android app: Provide a way to delete extra model files #4233
• User can upload to smartphone his/her own model files to his own device, from own computer or model files received from friend, etc.

Optionally you could add a setting in UI, in Settings window, allowing user to specify the local model file subdirectory. Which can have the default value of /sdcard/mnn-models , but also can be changed to other desired path.

[Juude]

I appreciate the feedback. We have a few concerns regarding this implementation:

Storage Permissions: Using /sdcard/ would require permissions that make it difficult to pass Google Play's review process due to Scoped Storage requirements.

Refactoring Effort: The download module currently uses symbolic links; moving the directory would necessitate a major architectural overhaul.

Alternative: We can look into providing a manual backup/export method to external storage, though this would only be available in dev versions (distributed outside of Google Play).

[mnba]

Thanks for considering. Addressing the concerns:

Storage Permissions: Using /sdcard/ would require permissions that make it difficult to pass Google Play's review process due to Scoped Storage requirements.

1 . OK, I get this, I missed the Android Storage API change occurred in Android v.10+.

Now normal apps (which are not file manager apps) can use so-called method of
app-specific external storage directory.
Example path
/sdcard/Android/data/com.example.app/files/
In this case you should use the directory at:
/sdcard/Android/data/com.alibaba.mnnllm.android.release/files
Quoting ChatGPT

...technically it is the correct place for large app-managed files.
Advantages:

• ✔ No special storage permission needed
• ✔ Allowed by Scoped Storage
• ✔ Passes Google Play review
• ✔ Files are visible via USB or some file managers
• ✔ Suitable for large model files

To access the files User should use some well-known Android File manager apps, like Total commander and give permission to access the directory /sdcard/Android/data/ via built-in "Files" app.

This way can also use your suggested manual backup/export tool or app function.

Another important keyword in this topic is SAF,
Storage Access Framework (SAF).

ChatGPT says

This way avoids Play Store problems entirely.

I used the same ChatGPT in anonymous mode to generate the sample Kotlin code for copying files to and from "app-specific external storage directory" and seems it solved the task.

Refactoring Effort: The download module currently uses symbolic links; moving the directory would necessitate a major architectural overhaul.

2 . I cannot estimate the exact volume of efforts needed for refactoring, but I can suppose that usage of symlink in general case is not required for such app.
Maybe you could find a solution.

Alternative: We can look into providing a manual backup/export method to external storage, though this would only be available in dev versions (distributed outside of Google Play).

3 . As I said in point 1 using SAF and "app-specific external storage directory" will remove necessity of dev versions (distributed outside of Google Play).

Overall, the only problem I can see now is that refactoring related issue, isn't it?