using System.Runtime.InteropServices;
//-----------------------------------------------------------------------
public const int WM_NCLBUTTONDOWN = 0xA1;
public const int HT_CAPTION = 0x2;
[DllImportAttribute("user32.dll")]
public static extern int SendMessage(IntPtr hWnd,
int Msg, int wParam, int lParam);
[DllImportAttribute("user32.dll")]
public static extern bool ReleaseCapture();
//-------------------------------------------------------------------------
private void frm_MouseDown(object sender, MouseEventArgs e)
{
if (e.Button == MouseButtons.Left )
{
ReleaseCapture();
SendMessage(Handle, WM_NCLBUTTONDOWN, HT_CAPTION, 0);
}
}