Xamarin.Android上某些文件上的UnauthorizedAccessException

Question

I have some files in the Environment.SpecialFolder.Personal folder, say A and B for simplicity.

File A was created by the app, while file B was copied in via Android Studio's Device File Explorer. The app can open A, but B throws an UnauthorizedAccessException .

To open, after checking whether the File.Exists , I use

FileStream fileStream = new FileStream(file, FileMode.Open, FileAccess.Read, FileShare.None);

File.Exists correctly returns that the files exists, but creating the new FileStream fails for B.

I have already tried changing the user/group of the B file, as well as changing the permissions to match the info from file A.

I am debugging this in an Android emulator with version 7.1.1 API level 25.

How can I solve the problem, or at least find more information about the problem?

Edit: I've tried a 8.1 API level 27 with no success, but on a physical device LG D618 with 5.0 API 21 it works.

How can I make the emulator work?

Answer 1

I think the reason is that you need to ask the permission at runtime.

According to the official documentation :

You declare that your app needs a permission by listing the permission in the app manifest and then requesting that the user approve each permission at runtime (on Android 6.0 and higher).

You physical device is running on Android 5.0, so it works fine.

You could refer to this blog for how to do it in xamarin.