about api called in c#

Hi expert: i come from China,I would very appreciate for your help! I am trying to learn of c# and windows api,so i implement api functions in c#. now,in my first step,i want to create a window by CreateWindow,which must deal with struct WNDCLASS and function RegisterClass;the error occurs at which i call function RegisterClass, is about parameter can not match to the function. the following is my code: //const define area public const long CS_VREDRAW = 0x1; public const long CS_HREDRAW = 0x2; public const long IDC_ARROW = 32512; private const String myWindowClassName="Hello"; //WNDCLASS struct define public struct WNDCLASS { public Int32 style; public long lpfnwndproc; public long cbClsextra; public long cbWndExtra2; public IntPtr hInstance; public IntPtr hIcon; public IntPtr hCursor; public IntPtr hbrBackground; public String lpszMenuName; public String lpszClassName; } //api function RegisterClass [DllImport("user32.dll",EntryPoint="RegisterClassA",CharSet=CharSet.Unicode)] public static extern long RegisterClass(WNDCLASS Class); [DllImport("user32.dll",EntryPoint="DefWindowProcA",CharSet=CharSet.Unicode)] public static extern long DefWindowProc(IntPtr hWnd,long wMsg, long wParam, long lParam); //main function private bool MyRegisterClass() { WNDCLASS wndcls; try { wndcls.style=(Int32)CS_HREDRAW+(Int32)CS_VREDRAW; Type t=this.GetType(); MethodInfo m=t.GetMethod("MyWndProc"); wndcls.lpfnwndproc=(long)m.MethodHandle.Value; wndcls.cbClsextra=0; wndcls.cbWndExtra2=0; wndcls.hInstance=(IntPtr)Marshal.GetHINSTANCE(System.Reflection. Assembly.GetExecutingAssembly().GetModules()[0]).ToInt32(); wndcls.hIcon=(IntPtr)0; wndcls.hCursor=LoadCursor((IntPtr)0,IDC_ARROW); wndcls.hbrBackground=(IntPtr)COLOR_WINDOW; wndcls.lpszMenuName=null; wndcls.lpszClassName=myWindowClassName; return(RegisterClass(wndcls)!=0); //error occur here } catch(Exception e) { return false; } } //windows message process procedure public long MyWndProc(IntPtr hWnd,long message,long wParam,long lParam) { return DefWindowProc(hWnd,message,wParam,lParam); } and thank you for your help!