WPF: Drag & Drop virtual folder from WPF to File Explorer

Alex SSB 20

Hi, I am developing ADB Explorer, a UI for ADB in WPF.

I am trying to implement support for Drag & Drop to Push / Pull files between PC and a device connected via ADB, and while accepting files dragged into the app is quite easy since I can just use the provided path, its the other direction that I still can't get right. Namely, dragging a folder from the app to File Explorer.

I started by using VirtualFileDataObject class to transfer the files as streams, which is what's usually recommended for files that do not yet exist on the PC, but since ADB works best when transferring files instead of reading them as bytes, the solution is to pull the files into a temp folder, and send File Explorer the data from there.

Now although this works, this does require telling the shell all of the files to be transferred beforehand, which requires building a hierarchy tree before the drag begins, which in turn might take some time depending on the amount of files inside the selected folder. (FileGroupDescriptorW, FileContents)

I also tried using FileDrop together with InShellDragLoop which is used to tell the shell that not all of the required files are ready for transfer, but File Explorer didn't wait for me to set InShellDragLoop to FALSE and just copied (at best) the empty folder from the temp location.

So my question is what is the best approach here, and how can I make File Explorer wait for my transfer to my temp folder finish before taking the files from there?

Hongrui Yu-MSFT 1,605 Reputation points Microsoft Vendor

2024-08-26T09:03:44.81+00:00

Hi,@Alex SSB. Welcome to Microsoft Q&A.

Could you provide the implementation logic for this part? Is it possible to wait until the file is ready before calling the shell to transfer it?
Alex SSB 20 Reputation points

2024-08-26T16:32:45.9733333+00:00
I used and modified the VirtualFileDataObject class, as this was the best solution I found.

Is it possible to wait until the file is ready before calling the shell to transfer it?

This means the hierarchy tree of the selected folder needs to be ready before it can be sent to the shell, and the time required to do this depends on:

The size of the selected folder (in sub-folders and files)

How fast is the connection to the Android device

How busy the device is

So, with small folders it is usually an acceptable delay in case the tree is generated upon selecting the folder. But folders like /sdcard/Android/media/com.whatsapp/WhatsApp/Media for example, which may contain thousands of files, can take up to 10 seconds to build the tree. Naturally, I can indicate that the files are being prepared for drag, and only when ready, send them to the shell. But that requires the user to wait before dropping, so I wondered whether there is a better way.

I looked at what 7zip does when dragging files from inside an archive to File Explorer. It sends only a FileDrop object which is the path of a temp folder which is created on drag start, and somehow File Explorer waits for the extracting to complete before moving the files from the temp folder. I couldn't find anything else that's done there, even after inspecting the open source code.

If I could solve the issue of File Explorer disregarding me setting InShellDragLoop, maybe that will be the solution.
Hongrui Yu-MSFT 1,605 Reputation points Microsoft Vendor

2024-08-27T03:22:27.1633333+00:00

Hi,@Alex SSB.

I can't find InShellDragLoop in the link you gave.

In addition, Microsoft Q&A does not support the modification of large projects and requires a minimal code sample that could reproduce the problem.

Alex SSB 20

Sorry about that, since the code didn't really work, I didn't commit it. Here is the handling of InShellDragLoop:

private static class DragLoop
{
    private static byte[] FALSE => new byte[] { 0, 0, 0, 0 };
    private static byte[] TRUE => new byte[] { 1, 0, 0, 0 };

    private static VirtualFileDataObject dataObject;

    private static int totalCount = 0;

    private static int completedCount = 0;

    private static void AddCompletedOp()
    {
        completedCount++;

        if (completedCount < totalCount)
            return;

        // Set InShellDragLoop value to 0 == loop completed
        dataObject.UpdateData(VirtualFileDataObject.DRAGLOOP, FALSE);

        // Return everything to initial state
        totalCount = 0;
        completedCount = 0;
    }

    public static void SetDragLoop(VirtualFileDataObject vfdo, IEnumerable<FileSyncOperation> fileOperations)
    {
        dataObject = vfdo;

        // Add InShellDragLoop object to the VFDO, with value of 1 == loop in progress
        vfdo.SetData(VirtualFileDataObject.DRAGLOOP, TRUE);
        totalCount = fileOperations.Count();

        foreach (var fileOp in fileOperations)
        {
            // Add the event handler to all operations
            fileOp.PropertyChanged += FileOp_PropertyChanged;
        }

        void FileOp_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            if (e.PropertyName == nameof(FileSyncOperation.Status) && ((FileSyncOperation)sender).Status
                is not FileOperation.OperationStatus.InProgress
                and not FileOperation.OperationStatus.Waiting)
            {
                // Increase the counter if the operation is done, even if failed
                AddCompletedOp();

                // Remove the event handler from the operation since file operations are not disposed of regularly
                ((FileSyncOperation)sender).PropertyChanged -= FileOp_PropertyChanged;
            }
        }
    }
}

Regarding the IEnumerable<FileSyncOperation> - those are the operations for each of the selected items (to transfer from device to PC), and they are started when the drop happens.

Hongrui Yu-MSFT 1,605 Reputation points Microsoft Vendor

2024-08-28T06:38:59.0066667+00:00
Hi,@Alex SSB.

I read your code, maybe this method is not easy to implement.

If you want to implement drag and drop file transfer like 7z, you could consider including the process of building the folder hierarchy tree in the file transfer process.

That is, when the user drags a local file, you only need to get the address of the local file first. When the user finishes dragging, you build the folder hierarchy tree and file transfer based on the address, and record the folder hierarchy tree and file transfer time together in the progress bar. (Large files themselves take a long time to transfer, and adding 10 seconds to build the tree will not significantly affect the user experience).

The following is a simple example for getting the address of the folder dragged into the project.

<Window … AllowDrop="True" Drop="Window_Drop"> <Grid> </Grid> </Window>

public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); } private void Window_Drop(object sender, DragEventArgs e) { string msg = "Drop"; if (e.Data.GetDataPresent(DataFormats.FileDrop)) { msg = ((System.Array)e.Data.GetData(DataFormats.FileDrop)).GetValue(0).ToString(); } MessageBox.Show(msg); } }
Alex SSB 20 Reputation points

2024-08-28T16:54:35.4066667+00:00

Hi @Hongrui Yu-MSFT .

Thanks again, but I didn't mean dragging files into the app - as you said so yourself, this part is a walk in the park. I meant dragging files from the app to the PC, non-local files.
Hongrui Yu-MSFT 1,605 Reputation points Microsoft Vendor

2024-08-29T08:02:55.81+00:00

Hi,@Alex SSB.

This forum is for general discussion of .NET and WPF issues. We can only provide information about .NET drag and drop. For ADB-related drag and drop, please go to the ADB forum to ask.
Alex SSB 20 Reputation points

2024-08-29T19:08:05.42+00:00

Ok, so let me rephrase my question then:

Suppose I have a folder, the structure of which I do not know yet, and which does not exist on the PC. I need to allow the user to drag this folder from my app into File Explorer, and for File Explorer to accept the drop immediately. Only after the drop is accepted by File Explorer, can I begin transferring the folder with its contents to a temp folder, from which I want File Explorer to then take (cut - move) the whole of it.

How do I make File Explorer wait for me to complete the transfer to the temp folder, before it begins moving the folder from there?
Alex SSB 20 Reputation points

2024-08-29T19:16:16.66+00:00

Ok so let me rephrase my question:

Suppose I have a virtual folder, the structure of which I do not know yet. I need to allow the user to drag this folder from my app into File Explorer, and for File Explorer to accept the drop immediately. Only after the drop has been accepted and initiated, can I begin transferring the folder with its contents to a temporary location. I want File Explorer to wait for me to complete this operation before it begins taking (cut - move) the folder with its contents from the temporary location.

How do I make File Explorer wait for the operation to complete?
Hongrui Yu-MSFT 1,605 Reputation points Microsoft Vendor

2024-08-30T08:30:54.1+00:00

Hi,@Alex SSB.

I can't make the file explorer wait for the operation to complete. Immediate transmission when dragging is completed should be an inherent function of the operating system, but you could refer to the following design ideas to transfer virtual files to the PC.

Core idea: only get the address where the virtual file is to be stored from the file explorer, and do not participate in the drag-and-drop transfer operation of the file.

The file explorer could be embedded in the WPF program in the form of a control. When you start dragging a virtual file, execute the start drag event and disable the file explorer control. When the user drags the virtual file into the area of the file explorer control and ends the drag, execute the drag end event, and get the current navigation address of the file explorer in the drag end event. At this time, you could create a temporary folder based on the navigation address and perform other operations you need, and then transfer the file

1 answer

youzeliang 480 Reputation points

2024-08-24T13:08:34.4266667+00:00
To enable smooth Drag & Drop functionality from your WPF application to File Explorer, especially when dealing with virtual folders that need to be populated during the drag operation, you might consider using a combination of delayed rendering and asynchronous operations to manage the file transfer process.

Here's a strategy that could work:

Delayed File Enumeration:

Asynchronous File Enumeration: Start by preparing a list of files asynchronously as soon as the drag operation starts. Instead of blocking the UI, show a "Preparing files..." message or a progress indicator.

Manual Completion of DataObject: Use the FileGroupDescriptorW format to notify File Explorer about the files to be transferred, but instead of sending all the files upfront, send placeholders and manage the actual file generation or transfer asynchronously.

Handling InShellDragLoop:

You can set InShellDragLoop to indicate that not all files are ready. However, ensure you do this correctly:

Implement a loop that monitors the status of the file transfer.

Update InShellDragLoop to FALSE only when the file transfer is complete and the files are available in the temp folder.

Use a dedicated background worker or task to handle the file transfer and update the shell as files become ready.
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Alex SSB 20 Reputation points

2024-08-24T13:43:04.0833333+00:00

Thanks, but with FileGroupDescriptorW I still have the time it takes to build the directory tree, which can take some seconds depending on the size of the folder. When I tried replacing / adding to the data during the transfer, File Explorer either aborted the transfer or proceeded with the original list.

Regarding InShellDragLoop + FileDrop, I have no idea why File Explorer still didn't wait for it to change to FALSE, but just didn't perform the transfer.
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WPF: Drag & Drop virtual folder from WPF to File Explorer

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