C#

[DllImport("User32.dll")]
public static extern bool SystemParametersInfo(int Action, 
                                     int Param, 
                                     IntPtr lpParam, 
                                     int WinIni);

const int SPI_GETNONCLIENTMETRICS = 41;

NONCLIENTMETRICS ncm = new NONCLIENTMETRICS();

int size = ncm.cbSize = Marshal.SizeOf(typeof(NONCLIENTMETRICS));
IntPtr pncmetrics = Marshal.AllocHGlobal(size);
Marshal.StructureToPtr(ncm, pncmetrics, true);
bool b = SystemParametersInfo(SPI_GETNONCLIENTMETRICS, size, pncmetrics, 0); 
Marshal.PtrToStructure(pncmetrics,ncm); 
Marshal.FreeHGlobal(pncmetrics);

• Change the NONCLIENTMETRICS to a struct (NB: You'll have to remove the constructor.)
• Change the declaration to:
  
  cd

  [DllImport("User32.dll")]
  public static extern bool SystemParametersInfo(int Action, 
      int uiParam, ref NONCLIENTMETRICS pvParam, int WinIni);

• Change the call to:
  
  C#

  NONCLIENTMETRICS ncm = new NONCLIENTMETRICS();
  ncm.cbSize = Marshal.SizeOf(ncm);
  bool b = SystemParametersInfo(SPI_GETNONCLIENTMETRICS, 
      ncm.cbSize, ref ncm, 0);

using System;
using System.Runtime.InteropServices;
 
class App
{
    [StructLayout(LayoutKind.Sequential)]
    public struct LOGFONT
    {
        public int lfHeight;
        public int lfWidth;
        public int lfEscapement;
        public int lfOrientation;
        public int lfWeight;
        public byte lfItalic;
        public byte lfUnderline;
        public byte lfStrikeOut;
        public byte lfCharSet;
        public byte lfOutPrecision;
        public byte lfClipPrecision;
        public byte lfQuality;
        public byte lfPitchAndFamily;
        
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst=32)]
        public string lfFaceName;
    }
    
    [StructLayout(LayoutKind.Sequential)]
    public struct NONCLIENTMETRICS
    {
        public int cbSize;
        public int iBorderWidth;
        public int iScrollWidth;
        public int iScrollHeight;
        public int iCaptionWidth;
        public int iCaptionHeight;
        public LOGFONT  lfntCaptionFont;
        public int iSMCaptionWidth;
        public int iSMCaptionHeight;
        public LOGFONT lfntSMCaptionFont;
        public int iMenuWidth;
        public int iMenuHeight;
        public LOGFONT lfntMenuFont;
        public LOGFONT lfntStatusFont;
        public LOGFONT lfntMessageFont;
    }
    
    [DllImport("User32.dll")]
    public static extern bool SystemParametersInfo(
        int Action, int uiParam, 
        ref NONCLIENTMETRICS pvParam, int WinIni);
    
    static void Main()
    {
        const int SPI_GETNONCLIENTMETRICS = 41;
        
        try
        {
            NONCLIENTMETRICS ncm = new NONCLIENTMETRICS();
            ncm.cbSize = Marshal.SizeOf(ncm);
            
            bool b = SystemParametersInfo(
                SPI_GETNONCLIENTMETRICS, 
                ncm.cbSize, ref ncm, 0);
            
            if (b)
            {
                Console.WriteLine("Border Width: {0}", 
                    ncm.iBorderWidth);
    
                Console.WriteLine("Scroll Width: {0}", 
                    ncm.iScrollWidth);
    
                Console.WriteLine("Caption Font: {0}", 
                    ncm.lfntCaptionFont.lfFaceName);
            }
            else
                Console.WriteLine("Failed");
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
    }
}

Border Width: 1
Scroll Width: 17
Caption Font: Trebuchet MS

Stupidity dies.
The end of future offspring.
Evolution wins.
- A Darwin Awards Haiku

SendMessage( hHandle, WM_USER + 1, 0, 0 );

public virtual void WndProc( Message* m )
{
     if ( m->Msg == WM_USER + 1 )
     {
           // Here you can modify ar add control without any problems.
     }
}

public void AddControl(Control control)
{
  Control.Add(control);
}

...

myform.Invoke(((MyForm)myform).AddControl, new TextBox());