ElevatedDragDropManager.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Windows.Forms;

public class ElevatedDragDropManager : IMessageFilter
{
    #region "P/Invoke"
    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool ChangeWindowMessageFilterEx(IntPtr hWnd, uint msg, ChangeWindowMessageFilterExAction action, ref CHANGEFILTERSTRUCT changeInfo);

    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool ChangeWindowMessageFilter(uint msg, ChangeWindowMessageFilterFlags flags);

    [DllImport("shell32.dll")]
    private static extern void DragAcceptFiles(IntPtr hwnd, bool fAccept);

    [DllImport("shell32.dll")]
    private static extern uint DragQueryFile(IntPtr hDrop, uint iFile, [Out()]
StringBuilder lpszFile, uint cch);

    [DllImport("shell32.dll")]
    private static extern bool DragQueryPoint(IntPtr hDrop, ref POINT lppt);

    [DllImport("shell32.dll")]
    private static extern void DragFinish(IntPtr hDrop);

    [StructLayout(LayoutKind.Sequential)]
    private struct POINT
    {
        public int X;

        public int Y;
        public POINT(int newX, int newY)
        {
            X = newX;
            Y = newY;
        }

        public static implicit operator System.Drawing.Point(POINT p)
        {
            return new System.Drawing.Point(p.X, p.Y);
        }

        public static implicit operator POINT(System.Drawing.Point p)
        {
            return new POINT(p.X, p.Y);
        }
    }

    private enum MessageFilterInfo : uint
    {
        None,
        AlreadyAllowed,
        AlreadyDisAllowed,
        AllowedHigher
    }

    private enum ChangeWindowMessageFilterExAction : uint
    {
        Reset,
        Allow,
        Disallow
    }

    private enum ChangeWindowMessageFilterFlags : uint
    {
        Add = 1,
        Remove = 2
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct CHANGEFILTERSTRUCT
    {
        public uint cbSize;
        public MessageFilterInfo ExtStatus;
    }
    #endregion

    public static ElevatedDragDropManager Instance = new ElevatedDragDropManager();
    public event EventHandler<ElevatedDragDropArgs> ElevatedDragDrop;

    private const uint WM_DROPFILES = 0x233;
    private const uint WM_COPYDATA = 0x4a;

    private const uint WM_COPYGLOBALDATA = 0x49;
    private readonly bool IsVistaOrHigher = Environment.OSVersion.Version.Major >= 6;

    private readonly bool Is7OrHigher = (Environment.OSVersion.Version.Major == 6 && Environment.OSVersion.Version.Minor >= 1) || Environment.OSVersion.Version.Major > 6;

    public void EnableDragDrop(IntPtr hWnd)
    {
        if (Is7OrHigher)
        {
            CHANGEFILTERSTRUCT changeStruct = new CHANGEFILTERSTRUCT();
            changeStruct.cbSize = Convert.ToUInt32(Marshal.SizeOf(typeof(CHANGEFILTERSTRUCT)));
            ChangeWindowMessageFilterEx(hWnd, WM_DROPFILES, ChangeWindowMessageFilterExAction.Allow, ref changeStruct);
            ChangeWindowMessageFilterEx(hWnd, WM_COPYDATA, ChangeWindowMessageFilterExAction.Allow, ref changeStruct);
            ChangeWindowMessageFilterEx(hWnd, WM_COPYGLOBALDATA, ChangeWindowMessageFilterExAction.Allow, ref changeStruct);
        }
        else if (IsVistaOrHigher)
        {
            ChangeWindowMessageFilter(WM_DROPFILES, ChangeWindowMessageFilterFlags.Add);
            ChangeWindowMessageFilter(WM_COPYDATA, ChangeWindowMessageFilterFlags.Add);
            ChangeWindowMessageFilter(WM_COPYGLOBALDATA, ChangeWindowMessageFilterFlags.Add);
        }

        DragAcceptFiles(hWnd, true);
    }

    public bool PreFilterMessage(ref Message m)
    {
        if (m.Msg == WM_DROPFILES)
        {
            HandleDragDropMessage(m);
            return true;
        }
        return false;
    }

    private void HandleDragDropMessage(Message m)
    {
        dynamic sb = new StringBuilder(260);
        uint numFiles = DragQueryFile(m.WParam, 0xffffffffu, sb, 0);
        dynamic list = new List<string>();

        for (uint i = 0; i <= numFiles - 1; i++)
        {
            if (DragQueryFile(m.WParam, i, sb, Convert.ToUInt32(sb.Capacity) * 2) > 0)
            {
                list.Add(sb.ToString());
            }
        }

        POINT p = default(POINT);
        DragQueryPoint(m.WParam, ref p);
        DragFinish(m.WParam);

        dynamic args = new ElevatedDragDropArgs();
        args.HWnd = m.HWnd;
        args.Files = list;
        args.X = p.X;
        args.Y = p.Y;

        if (ElevatedDragDrop != null)
        {
            ElevatedDragDrop(this, args);
        }
    }
}

public class ElevatedDragDropArgs : EventArgs
{
    public IntPtr HWnd
    {
        get { return m_HWnd; }
        set { m_HWnd = value; }
    }
    private IntPtr m_HWnd;
    public List<string> Files
    {
        get { return m_Files; }
        set { m_Files = value; }
    }
    private List<string> m_Files;
    public int X
    {
        get { return m_X; }
        set { m_X = value; }
    }
    private int m_X;
    public int Y
    {
        get { return m_Y; }
        set { m_Y = value; }
    }

    private int m_Y;
    public ElevatedDragDropArgs()
    {
        Files = new List<string>();
    }
}