Unity & Android - Working with one file on few apps

Question

I am working with Unity 2021.3.4f1. Platform target: Android 11.

Aim: I want to create/delete/append/read data from one file stored in public folder (eg. Download) by few applications.

Problem: If I create a file in AppA then I can't read/write data on this file from AppB. I get an error:

Unauthorizedaccessexception: access to the path ... is denied.

Everything works fine if I works only on one app. It sounds like this file is signed by this app and any other app can't use this file.

I add some lines into android manifest:

In Debug.Log I can see that this permission (MANAGE_EXTERNAL_STORAGE) isn't allowed (i dont know why).

I tried to copy this file from Download folder into Application.temporaryCachePath but I have this same error.

Now, some lines of code:

using System;
using System.IO;
using TMPro;
using UnityEngine;

public class FileManager : MonoBehaviour
{
    [SerializeField] TMP_Text fileValue;

    private string fileName = "fileName.txt";

    private string GlobalPath => Path.Combine(GetAndroidInternalFilesDir(), "Download", fileName);

    private void Start()
    {
        LoadFromFile();
    }

    public void AddToFile(string value)
    {
        value += Environment.NewLine;

        using (var fs = new FileStream(GlobalPath, FileMode.Append, FileAccess.Write, FileShare.ReadWrite))
        {
            using (var sw = new StreamWriter(fs))
            {
                sw.Write(value);
                Debug.Log("AddToFile!");
            }
        }

        LoadFromFile();
    }

    private void LoadFromFile()
    {
        if (!File.Exists(GlobalPath))
        {
            Debug.Log("File not exists!");
            return;
        }

        using (var fs = new FileStream(GlobalPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
        {
            using (var sr = new StreamReader(fs))
            {
                fileValue.text = sr.ReadToEnd();
                Debug.Log("LoadFromFile!");
            }
        }
    }

    //https://stackoverflow.com/questions/39983451/unity-android-save-files-disappears-after-updating-an-app/39994912#39994912
    private static string GetAndroidInternalFilesDir()
    {
        string[] potentialDirectories = new string[]
        {
        "/mnt/sdcard",
        "/sdcard",
        "/storage/sdcard0",
        "/storage/sdcard1"
        };

        if (Application.platform == RuntimePlatform.Android)
        {
            for (int i = 0; i < potentialDirectories.Length; i++)
            {
                if (Directory.Exists(potentialDirectories[i]))
                {
                    return potentialDirectories[i];
                }
            }
        }

        Debug.LogError("Path not exists!");
        return "";
    }
}

I know Android 11 has made things difficult for memory file management. However, maybe there are any ideas how I could deal with this problem?

Or possibly some other method of transferring information between several applications on one device. Without internet access?

Unity & Android - Working with one file on few apps

0 Answers