Android: Keep an up to date record of local files relevant to the app

Question

I've been reading about Content Providers and the Media Store but I'm still not sure what's the best way to solve this common problem.

To simplify, let's say I want to create an app to read ebooks. Users will copy their ebooks in the device storage somehow (i.e: using the USB and their computer, from dropbox, email...). Ebooks might be in several formats (mobi, epub,...). Since those files are not media files, I cannot use the Media Store for that purpose. It's also important to note, that I don't want a concrete solution for certain kinds of files (such as ebooks in my example). I would like a solution valid for all kind of files, even the most exotic ones.

I would like to perform a scan of the device storage to display a list of the ebooks saved in the device. I guess that should be done the first time the app is launched and afterwards if the user wants to update the list.

The problem I see is that the user may delete some of the ebook files outside my app, so it may show some old entries which are not there anymore. Of course I can show an error message if the user selects a removed entry, but maybe there is a better solution to that.

My question is basically what is the best strategy to keep the file list up to date. With "best strategy" I mean, to avoid potential critical errors and making everything as much transparent to the user as possible.

Answer 1

I think showing an error message to the user when he selects a removed entry is currently the best approach. You can also start a background service to check the file list after the user started your app. In most cases the code will be faster than user's reactions. I think the app can update itself before the user interacts with data. Or you can show only a progress bar while updating the data, and show the data (books) when done.

Alternatively, there is FileObserver. But it is impossible, I think. You need a background service to watch for files. And that is not good for battery life and device's performance.