Is it possible to drag and drop a UWP StorageFile to desktop, created using CreateStreamedFileFromUriAsyc - winapi

Question

The goal:
What I want to do is drag a GridViewItem from a GridView in a UWP app outside of the app to the desktop explorer. During the drop event, I want to download a file from the internet and create a StorageFile that will be used to populate the DataPackage. I want this StorageFile to be copied to the desktop. Unfortunately, when a deferral is used for UWP Drag&Drop (using SetDataProvider), as soon as you leave the app window, the request is activated and you have to populate the DataPackage with the object to be transferred. So, it seemed to me that I would need to use a deferred type of StorageFile created with CreateStreamedFileFromUriAsyc.
I do not want to pre-download the data every time I start to do a drag and drop operation. I only want to download the data when I'm actually dropping it somewhere legitimate to copy.
I know how to drag and drop a pre-existing StorageFile from UWP to Explorer (desktop) using a deferred request.
I also know how to create a StorageFile using CreateStreamedFileFromUriAsyc that will gives you a StorageFile that downloads data only when the data is requested.
When I try to combine these two ideas, windows Explorer gives me the error 'interface is not supported.'.
If I use the exact same code, but just get the file contents by calling something like GetBasicPropertiesAsync during the deferred drag handler, it works only if I hold the drag over the desktop until the file is downloaded. I can see it finishing when the drag icon changes from the 'prohibited' icon to 'copy'. If I let go of the mouse button before it is done, no copy will occur and no errors are raised.
Obviously, I would like the drag and drop to download without having to manually start it on the deferred handler. Any ideas? Is this possible?
(Yes, I realize the code to create the correct file extension is wrong/incomplete, but that's irrelevant here...)
//DragStarted Handler in constructor
DragItemsStartedCommand = ReactiveCommand.Create<DragItemsStartingEventArgs>((e) =>
{
_dragItems = e.Items.Cast<ItemViewModel>();
e.Data.Properties.Title = "Transfer file";
e.Data.Properties.Description = "desscription of transfering a file";
e.Data.Properties.FileTypes.Add(StandardDataFormats.StorageItems);
e.Data.SetDataProvider(Windows.ApplicationModel.DataTransfer.StandardDataFormats.StorageItems, OnDeferredStorageFileRequestedHandler);
e.Data.RequestedOperation = DataPackageOperation.Copy;
});
//Deferred request handler
async void OnDeferredStorageFileRequestedHandler(DataProviderRequest request)
{
DataProviderDeferral deferral = request.GetDeferral();
try
{
Task<IEnumerable<StorageFile>> task = null;
await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, async () =>
{
task = DownloadStorageFiles();
});
var result = await task;
request.SetData(result);
}
catch (Exception ex)
{
// Handle the exception
}
finally
{
deferral.Complete();
Debug.WriteLine("deferral complete!!!");
}
}
//Create StorageFile with deferred loading Task
async Task<IEnumerable<StorageFile>> DownloadStorageFiles()
{
List<StorageFile> storageItems = new List<StorageFile>();
foreach (var item in _dragItems)
{
var request = new RestSharp.RestRequest();
var defaultItemType = ItemType.MSWord;
switch (item.MimeTypeTranslated)
{
case ItemType.GoogleDocument:
case ItemType.GoogleSpreadsheet:
case ItemType.GooglePresentation:
case ItemType.GoogleDrawing:
case ItemType.GoogleScript:
request.Resource = $"files/{item.File.id}/export";
request.AddParameter("mimeType", Statics.ItemTypeDictionary.First(x => x.Value == defaultItemType).Key);
break;
default:
request.Resource = $"files/{item.File.id}";
request.AddParameter("alt", "media");
break;
}
string fileName = "";
if (item.File.name.EndsWith($".{Statics.ItemExtensionDictionary[defaultItemType]}"))
fileName = $"{item.File.name}";
else
fileName = $"{item.File.name}.{Statics.ItemExtensionDictionary[defaultItemType]}";
var uri = account.Client.GetAuthorizedUriForDownload(request);
var thumbnail = RandomAccessStreamReference.CreateFromFile(await StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///StoreLogo.png")));
var storageFileDeferred = await StorageFile.CreateStreamedFileFromUriAsync(fileName, uri , thumbnail);
//var props = await storageFileDeferred.GetBasicPropertiesAsync();
storageItems.Add(file);
}
return storageItems;
}
GitHub repro of this problem:
https://github.com/limefrogyank/DragDeferredFileToDesktop
First page is a regular drag to desktop that works because StorageFile (+ underlying data) is already in assets folder
Second page shows the error generated when using a StorageFile that is created with CreateStreamedFileFromUriAsync.
Third page uses the same type of StorageFile, but with a hack to force the retrieval of data synchronously. Desktop freezes for a second until data is ready.

Answer 1

As of the recent Windows updates the drag n' drop of storage files on UWP apps is automatically handled by the system.
example gif.