How to use filegroupdescriptor to drag file to explorer c#

Question

I would like to drag and drop an element of a listbox to explorer. When the drag and drop is started, I need to prepare the file on demand and save it to a memory stream. Can you provide me with an example on how to do it using the FileGroupDescriptor data structure? Thanks. Andrea

Answer 1

you can find an example on how to do this here Transferring Virtual Files to Windows Explorer in C#; also some good info on the topic here: Outlook Drag and Drop in C#

In short what you have to do is to init the DataObject with FILEDESCRIPTOR (you can find its declaration details on pinvoke.net) structure(s) for file(s) getting transfered and their content. Below is an example on how you could transfer 1 file from winforms ListBox to explorer.

mouse down event handler for the listbox:

private void listBox1_MouseDown(object sender, MouseEventArgs e)
{
    DataObject dataObject = new DataObject();
    DragFileInfo filesInfo = new DragFileInfo("d:\\test.txt");

    using (MemoryStream infoStream = GetFileDescriptor(filesInfo),
                        contentStream = GetFileContents(filesInfo))
    {
        dataObject.SetData(CFSTR_FILEDESCRIPTORW, infoStream);
        dataObject.SetData(CFSTR_FILECONTENTS, contentStream);
        dataObject.SetData(CFSTR_PERFORMEDDROPEFFECT, null);

        DoDragDrop(dataObject, DragDropEffects.All);
    }
}

code needed to init the dataobject:

[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
struct FILEDESCRIPTOR
{
    public UInt32 dwFlags;
    public Guid clsid;
    public System.Drawing.Size sizel;
    public System.Drawing.Point pointl;
    public UInt32 dwFileAttributes;
    public System.Runtime.InteropServices.ComTypes.FILETIME ftCreationTime;
    public System.Runtime.InteropServices.ComTypes.FILETIME ftLastAccessTime;
    public System.Runtime.InteropServices.ComTypes.FILETIME ftLastWriteTime;
    public UInt32 nFileSizeHigh;
    public UInt32 nFileSizeLow;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst=260)]
    public String cFileName;
}

public const string CFSTR_PREFERREDDROPEFFECT = "Preferred DropEffect";
public const string CFSTR_PERFORMEDDROPEFFECT = "Performed DropEffect";
public const string CFSTR_FILEDESCRIPTORW = "FileGroupDescriptorW";
public const string CFSTR_FILECONTENTS = "FileContents";

public const Int32 FD_WRITESTIME = 0x00000020;
public const Int32 FD_FILESIZE = 0x00000040;
public const Int32 FD_PROGRESSUI = 0x00004000;

public struct DragFileInfo
{
    public string FileName;
    public string SourceFileName;
    public DateTime WriteTime;
    public Int64 FileSize;

    public DragFileInfo(string fileName)
    {
        FileName = Path.GetFileName(fileName);
        SourceFileName = fileName;
        WriteTime = DateTime.Now;
        FileSize = (new FileInfo(fileName)).Length;
    }
}

private MemoryStream GetFileDescriptor(DragFileInfo fileInfo)
{
    MemoryStream stream = new MemoryStream();
    stream.Write(BitConverter.GetBytes(1), 0, sizeof(UInt32));

    FILEDESCRIPTOR fileDescriptor = new FILEDESCRIPTOR();

    fileDescriptor.cFileName = fileInfo.FileName;
    Int64 fileWriteTimeUtc = fileInfo.WriteTime.ToFileTimeUtc();
    fileDescriptor.ftLastWriteTime.dwHighDateTime = (Int32)(fileWriteTimeUtc >> 32);
    fileDescriptor.ftLastWriteTime.dwLowDateTime = (Int32)(fileWriteTimeUtc & 0xFFFFFFFF);
    fileDescriptor.nFileSizeHigh = (UInt32)(fileInfo.FileSize >> 32);
    fileDescriptor.nFileSizeLow = (UInt32)(fileInfo.FileSize & 0xFFFFFFFF);
    fileDescriptor.dwFlags = FD_WRITESTIME | FD_FILESIZE | FD_PROGRESSUI;

    Int32   fileDescriptorSize = Marshal.SizeOf(fileDescriptor);
    IntPtr  fileDescriptorPointer = Marshal.AllocHGlobal(fileDescriptorSize);
    Byte[]  fileDescriptorByteArray = new Byte[fileDescriptorSize];

    try
    {
        Marshal.StructureToPtr(fileDescriptor, fileDescriptorPointer, true);
        Marshal.Copy(fileDescriptorPointer, fileDescriptorByteArray, 0, fileDescriptorSize);
    }
    finally
    {
        Marshal.FreeHGlobal(fileDescriptorPointer);
    }
    stream.Write(fileDescriptorByteArray, 0, fileDescriptorByteArray.Length);
    return stream;
}

private MemoryStream GetFileContents(DragFileInfo fileInfo)
{
    MemoryStream stream  = new MemoryStream();            
    using (BinaryReader reader = new BinaryReader(File.OpenRead(fileInfo.SourceFileName)))
    {
        Byte[] buffer = new Byte[fileInfo.FileSize];
        reader.Read(buffer, 0, (Int32)fileInfo.FileSize);
        if (buffer.Length == 0) buffer = new Byte[1];
        stream.Write(buffer, 0, buffer.Length);
    }
    return stream;
}

hope this will give you an idea on how to proceed, regards