Drag-and-Drop multiple Attached File From Outlook to C# Window Form

Question

I Use following code for single file drag and drop.

 private void FormRegion2_DragEnter_1(object sender, DragEventArgs e)
    {
        if (e.Data.GetDataPresent(DataFormats.FileDrop))
        { e.Effect = DragDropEffects.Copy; }
        //    or this tells us if it is an Outlook attachment drop
        else if (e.Data.GetDataPresent("FileGroupDescriptor"))
        { e.Effect = DragDropEffects.Copy; }
        //    or none of the above
        else
        { e.Effect = DragDropEffects.None; }
    }

  private void FormRegion2_DragDrop_1(object sender, DragEventArgs e)
    {
        string[] fileNames = null;


        if (e.Data.GetDataPresent(DataFormats.FileDrop, false) == true)
        {
            fileNames = (string[])e.Data.GetData(DataFormats.FileDrop);                
            foreach (string fileName in fileNames)
            {
            }
        }
        else if (e.Data.GetDataPresent("FileGroupDescriptor"))
        {
           object s = e.Data.GetData("FileGroupDescriptor");

            Stream theStream = (Stream)e.Data.GetData("FileGroupDescriptor");
            byte[] fileGroupDescriptor = new byte[512];
            theStream.Read(fileGroupDescriptor, 0, 512);

            StringBuilder fileName = new StringBuilder("");

            for (int i = 76; fileGroupDescriptor[i] != 0; i++)
            { fileName.Append(Convert.ToChar(fileGroupDescriptor[i])); }

            string theFile = fileName.ToString();             
            String fileName1 = System.IO.Path.GetFileName(theFile);                

        }

    }

My problem is i am not able to get multiple file name. How it is possible to get multiple file name

Thx

Answer 1

There is a bug in the answer by V_B. It is in the section:

case "FileGroupDescriptorW":

The original implementation below to determine the number of items in the array is a bit wonky, besides it would throw Memory corruption exeptions when we would drag files over an infragistics treeview on win 8.

Searching for "DRAG DROP WIN8 FILEGROUPDESCRIPTORW write protected memory" led me to a posting on

https://social.msdn.microsoft.com/Forums/en-US/c9871410-1069-4dcb-a87d-b9c86ccbdd43/marshalptrtostructure-problem-when-drag-drop-mail-items-from-outlook-express?forum=winforms

That explained that it's a problem with the marshaller and they suggested to use Marshal.ReadInt32 and then 'increase the pointer' and 'read each within a loop'

Seeing as that is what exactly is being done in the code below (which I did not write, ), I think that this was the authors intention all along. The site teases us with the promise of more info with another dead link.

I tried to edit the comment, but it was rejected by peer review. I guess working software is not important.

replace

object fileGroupDescriptorObject = Marshal.PtrToStructure(fileGroupDescriptorWPointer, typeof(NativeMethods.FILEGROUPDESCRIPTORW));
NativeMethods.FILEGROUPDESCRIPTORW fgd = (NativeMethods.FILEGROUPDESCRIPTORW)fileGroupDescriptorObject;
files = new NativeMethods.FILEDESCRIPTOR[fgd.cItems];
pdata = (IntPtr)((int)pdata + Marshal.SizeOf(pdata));
for (int index = 0; index < fgd.cItems; index++)   

with

int ITEMCOUNT = Marshal.ReadInt32(pdata);                
files = new NativeMethods.FILEDESCRIPTOR[ITEMCOUNT];
// Set our pointer offset to the beginning of the FILEDESCRIPTOR* array
pdata = (IntPtr)((long)pdata + Marshal.SizeOf(pdata));
// Walk the array, converting each FILEDESCRIPTOR* to a FILEDESCRIPTOR
for (int index = 0; index < ITEMCOUNT; index++)

Answer 2

I solve my problem Just add that code in any cs file.

using System;
using System.IO;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.ComTypes;
using System.Text;
using System.Reflection;
using System.Windows.Forms;

  namespace iwantedue.Windows.Forms
 {  

public class OutlookDataObject: System.Windows.Forms.IDataObject
{
    #region NativeMethods

    private class NativeMethods
    {
        [DllImport("kernel32.dll")]
        static extern IntPtr GlobalLock(IntPtr hMem);

        [DllImport("ole32.dll", PreserveSig = false)]
        public static extern ILockBytes CreateILockBytesOnHGlobal(IntPtr hGlobal, bool fDeleteOnRelease);

        [DllImport("OLE32.DLL", CharSet = CharSet.Auto, PreserveSig = false)]
        public static extern IntPtr GetHGlobalFromILockBytes(ILockBytes pLockBytes);

        [DllImport("OLE32.DLL", CharSet = CharSet.Unicode, PreserveSig = false)]
        public static extern IStorage StgCreateDocfileOnILockBytes(ILockBytes plkbyt, uint grfMode, uint reserved);

        [ComImport, InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid("0000000B-0000-0000-C000-000000000046")]
        public interface IStorage
        {
            [return: MarshalAs(UnmanagedType.Interface)]
            IStream CreateStream([In, MarshalAs(UnmanagedType.BStr)] string pwcsName, [In, MarshalAs(UnmanagedType.U4)] int grfMode, [In, MarshalAs(UnmanagedType.U4)] int reserved1, [In, MarshalAs(UnmanagedType.U4)] int reserved2);
            [return: MarshalAs(UnmanagedType.Interface)]
            IStream OpenStream([In, MarshalAs(UnmanagedType.BStr)] string pwcsName, IntPtr reserved1, [In, MarshalAs(UnmanagedType.U4)] int grfMode, [In, MarshalAs(UnmanagedType.U4)] int reserved2);
            [return: MarshalAs(UnmanagedType.Interface)]
            IStorage CreateStorage([In, MarshalAs(UnmanagedType.BStr)] string pwcsName, [In, MarshalAs(UnmanagedType.U4)] int grfMode, [In, MarshalAs(UnmanagedType.U4)] int reserved1, [In, MarshalAs(UnmanagedType.U4)] int reserved2);
            [return: MarshalAs(UnmanagedType.Interface)]
            IStorage OpenStorage([In, MarshalAs(UnmanagedType.BStr)] string pwcsName, IntPtr pstgPriority, [In, MarshalAs(UnmanagedType.U4)] int grfMode, IntPtr snbExclude, [In, MarshalAs(UnmanagedType.U4)] int reserved);
            void CopyTo(int ciidExclude, [In, MarshalAs(UnmanagedType.LPArray)] Guid[] pIIDExclude, IntPtr snbExclude, [In, MarshalAs(UnmanagedType.Interface)] IStorage stgDest);
            void MoveElementTo([In, MarshalAs(UnmanagedType.BStr)] string pwcsName, [In, MarshalAs(UnmanagedType.Interface)] IStorage stgDest, [In, MarshalAs(UnmanagedType.BStr)] string pwcsNewName, [In, MarshalAs(UnmanagedType.U4)] int grfFlags);
            void Commit(int grfCommitFlags);
            void Revert();
            void EnumElements([In, MarshalAs(UnmanagedType.U4)] int reserved1, IntPtr reserved2, [In, MarshalAs(UnmanagedType.U4)] int reserved3, [MarshalAs(UnmanagedType.Interface)] out object ppVal);
            void DestroyElement([In, MarshalAs(UnmanagedType.BStr)] string pwcsName);
            void RenameElement([In, MarshalAs(UnmanagedType.BStr)] string pwcsOldName, [In, MarshalAs(UnmanagedType.BStr)] string pwcsNewName);
            void SetElementTimes([In, MarshalAs(UnmanagedType.BStr)] string pwcsName, [In] System.Runtime.InteropServices.ComTypes.FILETIME pctime, [In] System.Runtime.InteropServices.ComTypes.FILETIME patime, [In] System.Runtime.InteropServices.ComTypes.FILETIME pmtime);
            void SetClass([In] ref Guid clsid);
            void SetStateBits(int grfStateBits, int grfMask);
            void Stat([Out]out System.Runtime.InteropServices.ComTypes.STATSTG pStatStg, int grfStatFlag);
        }

        [ComImport, Guid("0000000A-0000-0000-C000-000000000046"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        public interface ILockBytes
        {
            void ReadAt([In, MarshalAs(UnmanagedType.U8)] long ulOffset, [Out, MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] byte[] pv, [In, MarshalAs(UnmanagedType.U4)] int cb, [Out, MarshalAs(UnmanagedType.LPArray)] int[] pcbRead);
            void WriteAt([In, MarshalAs(UnmanagedType.U8)] long ulOffset, IntPtr pv, [In, MarshalAs(UnmanagedType.U4)] int cb, [Out, MarshalAs(UnmanagedType.LPArray)] int[] pcbWritten);
            void Flush();
            void SetSize([In, MarshalAs(UnmanagedType.U8)] long cb);
            void LockRegion([In, MarshalAs(UnmanagedType.U8)] long libOffset, [In, MarshalAs(UnmanagedType.U8)] long cb, [In, MarshalAs(UnmanagedType.U4)] int dwLockType);
            void UnlockRegion([In, MarshalAs(UnmanagedType.U8)] long libOffset, [In, MarshalAs(UnmanagedType.U8)] long cb, [In, MarshalAs(UnmanagedType.U4)] int dwLockType);
            void Stat([Out]out System.Runtime.InteropServices.ComTypes.STATSTG pstatstg, [In, MarshalAs(UnmanagedType.U4)] int grfStatFlag);
        }

        [StructLayout(LayoutKind.Sequential)]
        public sealed class POINTL
        {
            public int x;
            public int y;
        }

        [StructLayout(LayoutKind.Sequential)]
        public sealed class SIZEL
        {
            public int cx;
            public int cy;
        }

        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
        public sealed class FILEGROUPDESCRIPTORA
        {
            public uint cItems;
            public FILEDESCRIPTORA[] fgd;
        }

        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
        public sealed class FILEDESCRIPTORA
        {
            public uint dwFlags;
            public Guid clsid;
            public SIZEL sizel;
            public POINTL pointl;
            public uint dwFileAttributes;
            public System.Runtime.InteropServices.ComTypes.FILETIME ftCreationTime;
            public System.Runtime.InteropServices.ComTypes.FILETIME ftLastAccessTime;
            public System.Runtime.InteropServices.ComTypes.FILETIME ftLastWriteTime;
            public uint nFileSizeHigh;
            public uint nFileSizeLow;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
            public string cFileName;
        }

        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
        public sealed class FILEGROUPDESCRIPTORW
        {
            public uint cItems;
            public FILEDESCRIPTORW[] fgd;
        }

        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
        public sealed class FILEDESCRIPTORW
        {
            public uint dwFlags;
            public Guid clsid;
            public SIZEL sizel;
            public POINTL pointl;
            public uint dwFileAttributes;
            public System.Runtime.InteropServices.ComTypes.FILETIME ftCreationTime;
            public System.Runtime.InteropServices.ComTypes.FILETIME ftLastAccessTime;
            public System.Runtime.InteropServices.ComTypes.FILETIME ftLastWriteTime;
            public uint nFileSizeHigh;
            public uint nFileSizeLow;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
            public string cFileName;
        }
    }

    #endregion

    #region Property(s)

    /// <summary>
    /// Holds the <see cref="System.Windows.Forms.IDataObject"/> that this class is wrapping
    /// </summary>
    private System.Windows.Forms.IDataObject underlyingDataObject;



    private System.Runtime.InteropServices.ComTypes.IDataObject comUnderlyingDataObject;



    private System.Windows.Forms.IDataObject oleUnderlyingDataObject;
    private MethodInfo getDataFromHGLOBLALMethod;
    #endregion

    #region Constructor(s)

    public OutlookDataObject(System.Windows.Forms.IDataObject underlyingDataObject)
    {

        this.underlyingDataObject = underlyingDataObject;
        this.comUnderlyingDataObject = (System.Runtime.InteropServices.ComTypes.IDataObject)this.underlyingDataObject;

        FieldInfo innerDataField = this.underlyingDataObject.GetType().GetField("innerData", BindingFlags.NonPublic | BindingFlags.Instance);
        this.oleUnderlyingDataObject = (System.Windows.Forms.IDataObject)innerDataField.GetValue(this.underlyingDataObject);
        this.getDataFromHGLOBLALMethod = this.oleUnderlyingDataObject.GetType().GetMethod("GetDataFromHGLOBLAL", BindingFlags.NonPublic | BindingFlags.Instance);
    }

    #endregion

    #region IDataObject Members

    public object GetData(Type format)
    {
        return this.GetData(format.FullName);
    }


    public object GetData(string format)
    {
        return this.GetData(format, true);
    }

    public object GetData(string format, bool autoConvert)
    {
        switch(format)
        {
            case "FileGroupDescriptor":
                IntPtr fileGroupDescriptorAPointer = IntPtr.Zero;
                try
                {
                    //use the underlying IDataObject to get the FileGroupDescriptor as a MemoryStream
                    MemoryStream fileGroupDescriptorStream = (MemoryStream)this.underlyingDataObject.GetData("FileGroupDescriptor", autoConvert);
                    byte[] fileGroupDescriptorBytes = new byte[fileGroupDescriptorStream.Length];
                    fileGroupDescriptorStream.Read(fileGroupDescriptorBytes, 0, fileGroupDescriptorBytes.Length);
                    fileGroupDescriptorStream.Close();

                    //copy the file group descriptor into unmanaged memory 
                    fileGroupDescriptorAPointer = Marshal.AllocHGlobal(fileGroupDescriptorBytes.Length);
                    Marshal.Copy(fileGroupDescriptorBytes, 0, fileGroupDescriptorAPointer, fileGroupDescriptorBytes.Length);

                    //marshal the unmanaged memory to to FILEGROUPDESCRIPTORA struct
                    object fileGroupDescriptorObject = Marshal.PtrToStructure(fileGroupDescriptorAPointer, typeof(NativeMethods.FILEGROUPDESCRIPTORA));
                    NativeMethods.FILEGROUPDESCRIPTORA fileGroupDescriptor = (NativeMethods.FILEGROUPDESCRIPTORA)fileGroupDescriptorObject;

                    //create a new array to store file names in of the number of items in the file group descriptor
                    string[] fileNames = new string[fileGroupDescriptor.cItems];

                    //get the pointer to the first file descriptor
                    IntPtr fileDescriptorPointer = (IntPtr)((int)fileGroupDescriptorAPointer + Marshal.SizeOf(fileGroupDescriptor.cItems));

                    //loop for the number of files acording to the file group descriptor
                    for(int fileDescriptorIndex = 0;fileDescriptorIndex < fileGroupDescriptor.cItems;fileDescriptorIndex++)
                    {

                        //marshal the pointer top the file descriptor as a FILEDESCRIPTORA struct and get the file name
                        NativeMethods.FILEDESCRIPTORA fileDescriptor = (NativeMethods.FILEDESCRIPTORA)Marshal.PtrToStructure(fileDescriptorPointer, typeof(NativeMethods.FILEDESCRIPTORA));
                        fileNames[fileDescriptorIndex] = fileDescriptor.cFileName;

                        //move the file descriptor pointer to the next file descriptor
                        fileDescriptorPointer = (IntPtr)((int)fileDescriptorPointer + Marshal.SizeOf(fileDescriptor));
                    }

                    //return the array of filenames
                    return fileNames;
                }
                finally
                {
                    //free unmanaged memory pointer
                    Marshal.FreeHGlobal(fileGroupDescriptorAPointer);
                }

            case "FileGroupDescriptorW":
                //override the default handling of FileGroupDescriptorW which returns a
                //MemoryStream and instead return a string array of file names
                IntPtr fileGroupDescriptorWPointer = IntPtr.Zero;
                try
                {
                    //use the underlying IDataObject to get the FileGroupDescriptorW as a MemoryStream
                    MemoryStream fileGroupDescriptorStream = (MemoryStream)this.underlyingDataObject.GetData("FileGroupDescriptorW");
                    byte[] fileGroupDescriptorBytes = new byte[fileGroupDescriptorStream.Length];
                    fileGroupDescriptorStream.Read(fileGroupDescriptorBytes, 0, fileGroupDescriptorBytes.Length);
                    fileGroupDescriptorStream.Close();

                    //copy the file group descriptor into unmanaged memory
                    fileGroupDescriptorWPointer = Marshal.AllocHGlobal(fileGroupDescriptorBytes.Length);
                    Marshal.Copy(fileGroupDescriptorBytes, 0, fileGroupDescriptorWPointer, fileGroupDescriptorBytes.Length);

                    //marshal the unmanaged memory to to FILEGROUPDESCRIPTORW struct
                    object fileGroupDescriptorObject = Marshal.PtrToStructure(fileGroupDescriptorWPointer, typeof(NativeMethods.FILEGROUPDESCRIPTORW));
                    NativeMethods.FILEGROUPDESCRIPTORW fileGroupDescriptor = (NativeMethods.FILEGROUPDESCRIPTORW)fileGroupDescriptorObject;

                    //create a new array to store file names in of the number of items in the file group descriptor
                    string[] fileNames = new string[fileGroupDescriptor.cItems];

                    //get the pointer to the first file descriptor
                    //get the pointer to the first file descriptor
                    IntPtr fileDescriptorPointer = (IntPtr)((int)fileGroupDescriptorWPointer + Marshal.SizeOf(fileGroupDescriptor.cItems));


                    //loop for the number of files acording to the file group descriptor
                    for (int fileDescriptorIndex = 0; fileDescriptorIndex < fileGroupDescriptor.cItems; fileDescriptorIndex++)
                    {
                        //marshal the pointer top the file descriptor as a FILEDESCRIPTORW struct and get the file name
                        NativeMethods.FILEDESCRIPTORW fileDescriptor = (NativeMethods.FILEDESCRIPTORW)Marshal.PtrToStructure(fileDescriptorPointer, typeof(NativeMethods.FILEDESCRIPTORW));
                        fileNames[fileDescriptorIndex] = fileDescriptor.cFileName;

                        //move the file descriptor pointer to the next file descriptor
                        fileDescriptorPointer = (IntPtr)((int)fileDescriptorPointer + Marshal.SizeOf(fileDescriptor));
                    }

                    //return the array of filenames
                    return fileNames;
                }
                finally
                {
                    //free unmanaged memory pointer
                    Marshal.FreeHGlobal(fileGroupDescriptorWPointer);
                }

            case "FileContents":
                //override the default handling of FileContents which returns the
                //contents of the first file as a memory stream and instead return
                //a array of MemoryStreams containing the data to each file dropped

                //get the array of filenames which lets us know how many file contents exist
                string[] fileContentNames = (string[])this.GetData("FileGroupDescriptor");

                //create a MemoryStream array to store the file contents
                MemoryStream[] fileContents = new MemoryStream[fileContentNames.Length];

                //loop for the number of files acording to the file names
                for(int fileIndex = 0;fileIndex < fileContentNames.Length;fileIndex++)
                {
                    //get the data at the file index and store in array
                    fileContents[fileIndex] = this.GetData(format, fileIndex);
                }

                //return array of MemoryStreams containing file contents
                return fileContents;
        }

        //use underlying IDataObject to handle getting of data
        return this.underlyingDataObject.GetData(format, autoConvert);
    }

    /// <summary>
    /// Retrieves the data associated with the specified data format at the specified index.
    /// </summary>
    /// <param name="format">The format of the data to retrieve. See <see cref="T:System.Windows.Forms.DataFormats"></see> for predefined formats.</param>
    /// <param name="index">The index of the data to retrieve.</param>
    /// <returns>
    /// A <see cref="MemoryStream"/> containing the raw data for the specified data format at the specified index.
    /// </returns>
    public MemoryStream GetData(string format, int index)
    {
        //create a FORMATETC struct to request the data with
        FORMATETC formatetc = new FORMATETC();
        formatetc.cfFormat = (short)DataFormats.GetFormat(format).Id;
        formatetc.dwAspect = DVASPECT.DVASPECT_CONTENT;
        formatetc.lindex = index;
        formatetc.ptd = new IntPtr(0);
        formatetc.tymed = TYMED.TYMED_ISTREAM | TYMED.TYMED_ISTORAGE | TYMED.TYMED_HGLOBAL;

        //create STGMEDIUM to output request results into
        STGMEDIUM medium = new STGMEDIUM();

        //using the Com IDataObject interface get the data using the defined FORMATETC
        this.comUnderlyingDataObject.GetData(ref formatetc, out medium);

        //retrieve the data depending on the returned store type
        switch(medium.tymed)
        {
            case TYMED.TYMED_ISTORAGE:
                //to handle a IStorage it needs to be written into a second unmanaged
                //memory mapped storage and then the data can be read from memory into
                //a managed byte and returned as a MemoryStream

                NativeMethods.IStorage iStorage = null;
                NativeMethods.IStorage iStorage2 = null;
                NativeMethods.ILockBytes iLockBytes = null;
                System.Runtime.InteropServices.ComTypes.STATSTG iLockBytesStat;
                try
                {
                    //marshal the returned pointer to a IStorage object
                    iStorage = (NativeMethods.IStorage)Marshal.GetObjectForIUnknown(medium.unionmember);
                    Marshal.Release(medium.unionmember);

                    //create a ILockBytes (unmanaged byte array) and then create a IStorage using the byte array as a backing store
                    iLockBytes = NativeMethods.CreateILockBytesOnHGlobal(IntPtr.Zero, true);
                    iStorage2 = NativeMethods.StgCreateDocfileOnILockBytes(iLockBytes, 0x00001012, 0);

                    //copy the returned IStorage into the new IStorage
                    iStorage.CopyTo(0, null, IntPtr.Zero, iStorage2);
                    iLockBytes.Flush();
                    iStorage2.Commit(0);

                    //get the STATSTG of the ILockBytes to determine how many bytes were written to it
                    iLockBytesStat = new System.Runtime.InteropServices.ComTypes.STATSTG();
                    iLockBytes.Stat(out iLockBytesStat, 1);
                    int iLockBytesSize = (int)iLockBytesStat.cbSize;

                    //read the data from the ILockBytes (unmanaged byte array) into a managed byte array
                    byte[] iLockBytesContent = new byte[iLockBytesSize];
                    iLockBytes.ReadAt(0, iLockBytesContent, iLockBytesContent.Length, null);

                    //wrapped the managed byte array into a memory stream and return it
                    return new MemoryStream(iLockBytesContent);
                }
                finally
                {
                    //release all unmanaged objects
                    Marshal.ReleaseComObject(iStorage2);
                    Marshal.ReleaseComObject(iLockBytes);
                    Marshal.ReleaseComObject(iStorage);
                }

            case TYMED.TYMED_ISTREAM:
                //to handle a IStream it needs to be read into a managed byte and
                //returned as a MemoryStream

                IStream iStream = null;
                System.Runtime.InteropServices.ComTypes.STATSTG iStreamStat;
                try
                {
                    //marshal the returned pointer to a IStream object
                    iStream = (IStream)Marshal.GetObjectForIUnknown(medium.unionmember);
                    Marshal.Release(medium.unionmember);

                    //get the STATSTG of the IStream to determine how many bytes are in it
                    iStreamStat = new System.Runtime.InteropServices.ComTypes.STATSTG();
                    iStream.Stat(out iStreamStat, 0);
                    int iStreamSize = (int)iStreamStat.cbSize;

                    //read the data from the IStream into a managed byte array
                    byte[] iStreamContent = new byte[iStreamSize];
                    iStream.Read(iStreamContent, iStreamContent.Length, IntPtr.Zero);

                    //wrapped the managed byte array into a memory stream and return it
                    return new MemoryStream(iStreamContent);
                }
                finally
                {
                    //release all unmanaged objects
                    Marshal.ReleaseComObject(iStream);
                }

            case TYMED.TYMED_HGLOBAL:
                //to handle a HGlobal the exisitng "GetDataFromHGLOBLAL" method is invoked via
                //reflection

                return (MemoryStream)this.getDataFromHGLOBLALMethod.Invoke(this.oleUnderlyingDataObject, new object[] { DataFormats.GetFormat((short)formatetc.cfFormat).Name, medium.unionmember });
        }

        return null;
    }

    /// <summary>
    /// Determines whether data stored in this instance is associated with, or can be converted to, the specified format.
    /// </summary>
    /// <param name="format">A <see cref="T:System.Type"></see> representing the format for which to check. See <see cref="T:System.Windows.Forms.DataFormats"></see> for predefined formats.</param>
    /// <returns>
    /// true if data stored in this instance is associated with, or can be converted to, the specified format; otherwise, false.
    /// </returns>
    public bool GetDataPresent(Type format)
    {
        return this.underlyingDataObject.GetDataPresent(format);
    }

    /// <summary>
    /// Determines whether data stored in this instance is associated with, or can be converted to, the specified format.
    /// </summary>
    /// <param name="format">The format for which to check. See <see cref="T:System.Windows.Forms.DataFormats"></see> for predefined formats.</param>
    /// <returns>
    /// true if data stored in this instance is associated with, or can be converted to, the specified format; otherwise false.
    /// </returns>
    public bool GetDataPresent(string format)
    {
        return this.underlyingDataObject.GetDataPresent(format);
    }

    /// <summary>
    /// Determines whether data stored in this instance is associated with the specified format, using a Boolean value to determine whether to convert the data to the format.
    /// </summary>
    /// <param name="format">The format for which to check. See <see cref="T:System.Windows.Forms.DataFormats"></see> for predefined formats.</param>
    /// <param name="autoConvert">true to determine whether data stored in this instance can be converted to the specified format; false to check whether the data is in the specified format.</param>
    /// <returns>
    /// true if the data is in, or can be converted to, the specified format; otherwise, false.
    /// </returns>
    public bool GetDataPresent(string format, bool autoConvert)
    {
        return this.underlyingDataObject.GetDataPresent(format, autoConvert);
    }

    /// <summary>
    /// Returns a list of all formats that data stored in this instance is associated with or can be converted to.
    /// </summary>
    /// <returns>
    /// An array of the names that represents a list of all formats that are supported by the data stored in this object.
    /// </returns>
    public string[] GetFormats()
    {
        return this.underlyingDataObject.GetFormats();
    }


    public string[] GetFormats(bool autoConvert)
    {
        return this.underlyingDataObject.GetFormats(autoConvert);
    }

    /// <summary>
    /// Stores the specified data in this instance, using the class of the data for the format.
    /// </summary>
    /// <param name="data">The data to store.</param>
    public void SetData(object data)
    {
        this.underlyingDataObject.SetData(data);
    }

    /// <summary>
    /// Stores the specified data and its associated class type in this instance.
    /// </summary>
    /// <param name="format">A <see cref="T:System.Type"></see> representing the format associated with the data. See <see cref="T:System.Windows.Forms.DataFormats"></see> for predefined formats.</param>
    /// <param name="data">The data to store.</param>
    public void SetData(Type format, object data)
    {
        this.underlyingDataObject.SetData(format, data);
    }

    /// <summary>
    /// Stores the specified data and its associated format in this instance.
    /// </summary>
    /// <param name="format">The format associated with the data. See <see cref="T:System.Windows.Forms.DataFormats"></see> for predefined formats.</param>
    /// <param name="data">The data to store.</param>
    public void SetData(string format, object data)
    {
        this.underlyingDataObject.SetData(format, data);
    }

    /// <summary>
    /// Stores the specified data and its associated format in this instance, using a Boolean value to specify whether the data can be converted to another format.
    /// </summary>
    /// <param name="format">The format associated with the data. See <see cref="T:System.Windows.Forms.DataFormats"></see> for predefined formats.</param>
    /// <param name="autoConvert">true to allow the data to be converted to another format; otherwise, false.</param>
    /// <param name="data">The data to store.</param>
    public void SetData(string format, bool autoConvert, object data)
    {
        this.underlyingDataObject.SetData(format, autoConvert, data);
    }

    #endregion
}
}

And write drop function like that

    private void FormRegion2_DragDrop_1(object sender, DragEventArgs e)
    {           
        string[] fileNames = null;           

        if (e.Data.GetDataPresent(DataFormats.FileDrop, false) == true)
        {
            fileNames = (string[])e.Data.GetData(DataFormats.FileDrop);
            foreach (string fileName in fileNames)
            {
                // do what you are going to do with each filename
            }
        }
        else if (e.Data.GetDataPresent("FileGroupDescriptor"))
        {                               
            OutlookDataObject dataObject = new OutlookDataObject(e.Data);
            string[] filenames = (string[])dataObject.GetData("FileGroupDescriptor");                
            for (int fileIndex = 0; fileIndex < filenames.Length; fileIndex++)
            {                   
                //Write your logic here u get multiple file name here
            }               
        }
    }