public class Win32Api
{
  public const int WM_SYSCOMMAND = 0x112;
  public const int SC_DRAGMOVE = 0xF012;

  [DllImport("user32.Dll", EntryPoint = "ReleaseCapture")]
  public extern static void ReleaseCapture(); // 鼠標(biāo)捕獲
  [DllImport("user32.Dll", EntryPoint = "SendMessage")]
  public extern static void SendMessage(IntPtr hWnd, int wMsg, int wParam, int lParam); // 將消息發(fā)送給指定的窗口
}

private void pnlHeader_MouseDown(object sender, MouseEventArgs e)
{
  Win32Api.ReleaseCapture();
  Win32Api.SendMessage(this.Handle, Win32Api.WM_SYSCOMMAND, Win32Api.SC_DRAGMOVE, 0);
}

public const int WM_NCLBUTTONDOWN = 0x00A1;
public const int HTCAPTION = 2;

private void pnlHeader_MouseDown(object sender, MouseEventArgs e)
{
  if (e.Button == MouseButtons.Left)
  {
    // 釋放控件已捕獲的鼠標(biāo)
    pnlHeader.Capture = false;

    // 創(chuàng)建并發(fā)送WM_NCLBUTTONDOWN消息
    Message msg =
      Message.Create(this.Handle, Win32Api.WM_NCLBUTTONDOWN,
        new IntPtr(Win32Api.HTCAPTION), IntPtr.Zero);
    this.DefWndProc(ref msg);
  }
}