Xamarin.Android: Prevent Package folder from external storage on app Uninstall with scope storage?

Question

It'd be convenient if an application I'm writing stored some files to external storage permanently (so they persist after the application has been exited[destroyed]/Uninstalled). I want to take database backup and store some cache and log files. I am targeting Android-11 while previously I was having access to external storage. Is there any way I can have these files not to be removed on an uninstall? Help with example will be really appreciated.

Answer 1

You could save the file to the storage directory for public files on external storage as PUBLIC_EXTERNAL_STORAGE. https://learn.microsoft.com/en-us/xamarin/android/platform/files/external-storage?tabs=windows

I use the Download folder for example.

  var DIR=   Environment.GetExternalStoragePublicDirectory(Environment.DirectoryDownloads);
       
        var FILE=DIR + "/test.txt";
         
        using (FileOutputStream outfile = new FileOutputStream(FILE))
        {
            string line = "The very first line!";
            outfile.Write(System.Text.Encoding.ASCII.GetBytes(line));
            outfile.Close();
        }

Xamarin.Forms does not provide the api to access External storage, we have to implement it in each specific platform. You could use the Dependency Service. https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/dependency-service/introduction

Here is an example of denpendence service for your reference. Save image from an image box to gallery in Xamarin Forms

Starting with Android 6.0 or higher, we need a runtime permission check. You could check the example I down before. Xamarin.Forms WebView not working with WebRTC