Creating Files in Android 11 gives Access Denied error.

Question

I am trying to create file at Downloads Directory. Basically I want user to download excel file that resides in my app(In Android Assets folder). User will fill and upload it again. For downloading I do as follows

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);
            //}
        }
    }

even if I give required permission and set flag in AndroidManifest.xml, I am getting this error.

I had asked on SO as well. Here is the linklink I tried to implement answer as well. It worked for few times but after that same error comes.

Please help.

Thank you

Answer 1

Android 11 has a new storage update

storage

take a look to this:

xamarin-forms-accessing-external-storage-on-android-11-target-sdk-version-is-29

Answer 2

Hello,

Welcome to our Microsoft Q&A platform!

1.Try to create a service class in Android project, just as follows:

 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);  
            }  
        }  
    }  
}  

2.In MainActivity.cs, add the following code:

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

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

3.call Init method after Forms.Init:

 FilesManager.Init(this);  

Refer: https://stackoverflow.com/questions/66560359/xamarin-forms-how-to-define-scoped-storage-for-android-and-how-can-i-implement

Best Regards,

Jessie Zhang

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