问如何从WM_DROPFILES发送C#？

EN

using System;
using System.Data;
using System.Linq;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace StackOverflow
{
    public partial class BadDragDrop : Form
    {
        #region WINAPI

        [Serializable]
        [StructLayout(LayoutKind.Sequential)]
        struct POINT
        {
            public Int32 X;
            public Int32 Y;
        }

        [Serializable]
        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
        class DROPFILES
        {
            public Int32 size;
            public POINT pt;
            public Int32 fND;
            public Int32 WIDE;
        }

        const uint WM_DROPFILES = 0x0233;
        const uint WM_SETTEXT = 0x000C;

        [DllImport("Kernel32.dll", SetLastError = true)]
        static extern int GlobalLock(IntPtr Handle);

        [DllImport("Kernel32.dll", SetLastError = true)]
        static extern int GlobalUnlock(IntPtr Handle);

        [DllImport("user32.dll", SetLastError = true)]
        static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);

        #endregion

        public BadDragDrop()
        {
            InitializeComponent();
            textBox1.AllowDrop = true;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string textToSet = "Hello world\0";
            IntPtr p = Marshal.AllocHGlobal(textToSet.Length);
            Marshal.Copy(textToSet.Select(c => (byte)c).ToArray(), 0, p, textToSet.Length);
            int success = GlobalUnlock(p);
            SendMessage(textBox1.Handle, WM_SETTEXT, IntPtr.Zero, p);
            Marshal.FreeHGlobal(p);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            string filePath = @"C:\Windows\win.ini" + "\0\0";

            DROPFILES s = new DROPFILES()
            {
                size = Marshal.SizeOf<DROPFILES>(),
                pt = new POINT() { X = 10, Y = 10 },
                fND = 0,
                WIDE = 0,
            };

            int wparamLen = s.size + filePath.Length;

            IntPtr p = Marshal.AllocHGlobal(wparamLen);
            int iSuccess = GlobalLock(p);

            Marshal.StructureToPtr(s, p, false);
            Marshal.Copy(filePath.Select(c => (byte)c).ToArray(), 0, p + s.size, filePath.Length);

            iSuccess = GlobalUnlock(p);

            var verify = new byte[wparamLen];
            Marshal.Copy(p, verify, 0, wparamLen);

            var ipSuccess = SendMessage(textBox1.Handle, WM_DROPFILES, p, IntPtr.Zero);
            Marshal.FreeHGlobal(p);
        }

        private void textBox1_DragDrop(object sender, DragEventArgs e)
        {
            MessageBox.Show(this, "Drag drop!");
        }

        private void textBox1_DragOver(object sender, DragEventArgs e)
        {
            e.Effect = DragDropEffects.Copy;
        }
    }
}