Xamarin.Forms - How to define scoped storage for android and how can I implement it to downlaod files in Downloads directory?

Question

In my app I have given facility to download reports in PDF formats. Everything was good until I was testing my app on Android 10 and below. Recently I updated a device to Android 11 and now I am not able to download any file in shared storage. I am getting Access Denied error while downloading file.

I have given permission to read and write external storage

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

and my download path is

Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryDownloads).AbsolutePath;

I have also set android:requestLegacyExternalStorage="true" in AndroidManifest.xml

My code to download file looks like this

public async void DownloadSupplierSample(object sender, EventArgs e)
    {
        try
        {
            string basepath;
            if (Device.RuntimePlatform == Device.Android)
                basepath = DependencyService.Get<IDownloadPath>().GetDownloadsPath();
            else
                basepath = System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Personal), "..", "Library");

            PermissionStatus readstatus = await Permissions.CheckStatusAsync<Permissions.StorageRead>();
            PermissionStatus writestatus = await Permissions.CheckStatusAsync<Permissions.StorageWrite>();

            if (readstatus == PermissionStatus.Granted && writestatus == PermissionStatus.Granted)
            {
                DownloadSupplier(basepath);
            }
            else
            {
                var read = await Permissions.RequestAsync<Permissions.StorageRead>();
                var write = await Permissions.RequestAsync<Permissions.StorageWrite>();

                if (read == PermissionStatus.Granted && write == PermissionStatus.Granted)
                {
                    DownloadSupplier(basepath);
                }
            }
            await DisplayAlert("", "Sample is downaloaded at Downloads directory","Ok");
        }
        catch (Exception ex)
        {
        }
    }

    async void DownloadSupplier(string basepath)
    {
        using (var stream = await FileSystem.OpenAppPackageFileAsync("SupplierMaster.xlsx"))
        {
            string filename = $"SupplierMaster_{DateTime.Now.ToString("yyyyMMddHHmmss")}.xlsx";
            string filepath = Path.Combine(basepath, filename);

            byte[] bytes = Utils.Common.StreamToBytes(stream);
            File.WriteAllBytes(filepath, bytes);
            //using (Stream filestream = File.Create(filepath))
            //{
            //    //stream.Seek(0, SeekOrigin.Begin);
            //    stream.CopyTo(filestream);
            //}
        }
    }

I have tried setting flag from device as well from this link

How can I define scoped storage for my app ?

Any update how can I download PDF file in my downloads directory ?

Thank you.

Answer 1

I had the same issue a couple of months ago.

I found this on developer.android page: (https://developer.android.com/reference/android/os/Environment#getExternalStorageDirectory())

The first alternative (getExternalFilesDir) won't work as you want, files won't appear in the download directory, this location is internal to the app.

The second alternative is for media files.

I ended up using the third alternative. I created a service class in Android project, something like this:

public class FilesManager : IFilesManager
{
    private const int CREATE_FILE_REQUEST_CODE = 123;
    private static Context _context;
    
    public static void Init(Context context)
    {
        _context = context;
    }

    public async Task SaveFile(string fileName, byte[] content)
    { 
        Intent intent = new Intent(Intent.ActionCreateDocument);
        intent.AddCategory(Intent.CategoryOpenable);
        intent.SetType(your_file_mimeType);
        intent.PutExtra(Intent.ExtraTitle, fileName);

        var activity = (MainActivity)_context;
        var listener = new ActivityResultListener(activity);
        activity.StartActivityForResult(intent, CREATE_FILE_REQUEST_CODE);

        var result = await listener.Task;

        if (result == null)
        {
            // Cancelled by user
            return;
        }

        using (Stream os = _context.ContentResolver.OpenOutputStream(result.Data))
        {
            os?.Write(content);
            os?.Close();
        }
    }

    private class ActivityResultListener
    {
        private readonly TaskCompletionSource<Intent> Complete = new TaskCompletionSource<Intent>();
        public Task<Intent> Task { get { return this.Complete.Task; } }

        public ActivityResultListener(MainActivity activity)
        {
            // subscribe to activity results
            activity.ActivityResult += OnActivityResult;
        }

        private void OnActivityResult(int requestCode, Result resultCode, Intent data)
        {
            if(requestCode != CREATE_FILE_REQUEST_CODE)
            {
                return;
            }

            // unsubscribe from activity results
            var activity = (MainActivity)_context;
            activity.ActivityResult -= OnActivityResult;

            // process result
            if (resultCode == Result.Ok)
            {
                Complete.TrySetResult(data);
            }
            else
            {
                Complete.TrySetResult(null);
            }
        }
    }
}

In MainActivity.cs add:

public event Action<int, Result, Intent> ActivityResult;

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data) 
{
    ActivityResult?.Invoke(requestCode, resultCode, data); 
}

You can call Init method after Forms.Init:

FilesManager.Init(this);

Note: This method requires user interaction. The user will be prompted to choose the location where to save the file.

Answer 2

How can I define scoped storage for my app ?Any update how can I download PDF file in my downloads directory ?

Android 10 introduced a new storage paradigm for apps called scoped storage which changes the way apps store and access files on a device's external storage. If you target Android 10 (API level 29) or higher, set the value of requestLegacyExternalStorage to true in your app's manifest file.

<application android:requestLegacyExternalStorage="true" android:label="FormsSample.Android" android:theme="@style/MainTheme"></application>

Then request runtime write and read EXTERNAL_STORAGE permission before access download folder.

public void requestpermission()
{
    if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.WriteExternalStorage) != (int)Permission.Granted)
    {
        ActivityCompat.RequestPermissions(this, new string[] { Manifest.Permission.WriteExternalStorage }, 1);
    }


    if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.ReadExternalStorage) != (int)Permission.Granted)
    {
        ActivityCompat.RequestPermissions(this, new string[] { Manifest.Permission.ReadExternalStorage }, 1);
    }
}

Create interface IAccessFileService in Xamarin.Forms shared code.

public interface IAccessFileService
{
    void CreateFile(string FileName);
}

Implementing IAccessFileService interface on Android platform.You could use File.Exists(xx) to check if the folder exists, and use Directory.CreateDirectory(xx) to create the folder if not.

[assembly: Xamarin.Forms.Dependency(typeof(AccessFileImplement))]
namespace FormsSample.Droid
{
    public class AccessFileImplement : IAccessFileService
    {
        public void CreateFile(string FileName)
        {
            string text = "hello world";
            byte[] data = Encoding.ASCII.GetBytes(text);
            string rootPath = Path.Combine(Android.OS.Environment.ExternalStorageDirectory.AbsolutePath, Android.OS.Environment.DirectoryDownloads);
            var filePathDir = Path.Combine(rootPath, "folder");
            if (!File.Exists(filePathDir))
            {
                Directory.CreateDirectory(filePathDir);
            }
            string filePath = Path.Combine(filePathDir, FileName);
            File.WriteAllBytes(filePath, data);
        }

        
    }
}

So using dependencyservice to call android CreateFile method.

private void btn1_Clicked(object sender, EventArgs e)
{
    DependencyService.Get<IAccessFileService>().CreateFile("test.txt");
}