C# Definition:

[StructLayout(LayoutKind.Sequential)]
struct WNDCLASSEX
{
   public uint cbSize;
   public ClassStyles style;
   [MarshalAs(UnmanagedType.FunctionPtr)]
   public WndProc lpfnWndProc;
   public int cbClsExtra;
   public int cbWndExtra;
   public IntPtr hInstance;
   public IntPtr hIcon;
   public IntPtr hCursor;
   public IntPtr hbrBackground;
   public string lpszMenuName;
   public string lpszClassName;
   public IntPtr hIconSm;
}

VB Definition:

<StructLayout(LayoutKind.Sequential)> _
Structure WNDCLASSEX
   Public cbSize As UInteger
   Public style As ClassStyles
   <MarshalAs(UnmanagedType.FunctionPtr)>
   Public lpfnWndProc As WndProc
   Public cbClsExtra As Integer
   Public cbWndExtra As Integer
   Public hInstance As IntPtr
   Public hIcon As IntPtr
   Public hCursor As IntPtr
   Public hbrBackground As IntPtr
   Public lpszMenuName As String
   Public lpszClassName As String
   Public hIconSm As IntPtr

   ' Use this function to make a new one with cbSize already filled in.
   ' For example:
   'Dim WndClss As WNDCLASSEX = WNDCLASSEX.GetNew()
   Shared Function MakeNew()
      Dim nw as New WNDCLASSEX
      nw.cbSize=Marshal.SizeOf(GetType(WNDCLASSEX))
      return nw
   End Function
End Structure

IMPORTANT:

The two strings were previously defined at pinvoke.net as:

<MarshalAs(UnmanagedType.LPTStr)> _
Public lpszMenuName As String
<MarshalAs(UnmanagedType.LPTStr)> _
Public lpszClassName As String

The MarshalAs attributes cause class registration to fail. They have been removed.

User-Defined Types:

WndProc, ClassStyles

Notes:

• cbSize
• Specifies the size, in bytes, of this structure. Set this member to sizeof(WNDCLASSEX). Be sure to set this member before calling the GetClassInfoEx function.
• style
• Specifies the class style(s). This member can be any combination of the ClassStyles.
• lpfnWndProc
• Pointer to the window procedure. You must use the CallWindowProc function to call the window procedure. For more information, see WndProc.
• cbClsExtra
• Specifies the number of extra bytes to allocate following the window-class structure. The system initializes the bytes to zero.
• cbWndExtra
• Specifies the number of extra bytes to allocate following the window instance. The system initializes the bytes to zero. If an application uses WNDCLASSEX to register a dialog box created by using the CLASS directive in the resource file, it must set this member to DLGWINDOWEXTRA.
• hInstance
• Handle to the instance that contains the window procedure for the class.
• hIcon
• Handle to the class icon. This member must be a handle to an icon resource. If this member is NULL, the system provides a default icon.
• hCursor
• Handle to the class cursor. This member must be a handle to a cursor resource. If this member is NULL, an application must explicitly set the cursor shape whenever the mouse moves into the application's window.
• hbrBackground
• Handle to the class background brush. This member can be a handle to the physical brush to be used for painting the background, or it can be a color value. A color value must be one of the following standard system colors (the value 1 must be added to the chosen color). If a color value is given, you must convert it to one of the following HBRUSH types:
• COLOR_ACTIVEBORDER
• COLOR_ACTIVECAPTION
• COLOR_APPWORKSPACE
• COLOR_BACKGROUND
• COLOR_BTNFACE
• COLOR_BTNSHADOW
• COLOR_BTNTEXT
• COLOR_CAPTIONTEXT
• COLOR_GRAYTEXT
• COLOR_HIGHLIGHT
• COLOR_HIGHLIGHTTEXT
• COLOR_INACTIVEBORDER
• COLOR_INACTIVECAPTION
• COLOR_MENU
• COLOR_MENUTEXT
• COLOR_SCROLLBAR
• COLOR_WINDOW
• COLOR_WINDOWFRAME
• COLOR_WINDOWTEXT
• The system automatically deletes class background brushes when the class is unregistered by using UnregisterClass. An application should not delete these brushes.
• When this member is NULL, an application must paint its own background whenever it is requested to paint in its client area. To determine whether the background must be painted, an application can either process the WM_ERASEBKGND message or test the fErase member of the PAINTSTRUCT structure filled by the BeginPaint function.
• lpszMenuName
• Pointer to a null-terminated character string that specifies the resource name of the class menu, as the name appears in the resource file. If you use an integer to identify the menu, use the MAKEINTRESOURCE macro. If this member is NULL, windows belonging to this class have no default menu.
• lpszClassName
• Pointer to a null-terminated string or is an atom. If this parameter is an atom, it must be a class atom created by a previous call to the RegisterClass or RegisterClassEx function. The atom must be in the low-order word of lpszClassName; the high-order word must be zero.
• If lpszClassName is a string, it specifies the window class name. The class name can be any name registered with RegisterClass or RegisterClassEx, or any of the predefined control-class names.
• The maximum length for lpszClassName is 256.
• hIconSm
• Handle to a small icon that is associated with the window class. If this member is NULL, the system searches the icon resource specified by the hIcon member for an icon of the appropriate size to use as the small icon.