What is the correct designpattern for UI? - winapi

Question

I am making a small app for loading data from an external device. It uses a DLL.
I want to make the app running in one window. With the menu it should be possible to bring up the correct state of UI. I dont want to use dialogs or seperate windows.
My idea is to use a state variable and have the WM_PAINT message handle the different content of the windows (createwindowEx for different text and button items i.e.).
Is this the correct way of doing so? I have searched the internet, read Programming Windows and searched stackoverflow and could not find a simple example. It is always using different windows with dedicated winproc functions. It feels like i dont need that...
Can someone help me with a direction or small example/link ?
thx
EDIT:
I enclose the code that i have so far now. Can someone have a look on that, Thx.
#if defined _MSC_VER || defined __BORLANDC__
#define OEMRESOURCE
#endif
#pragma comment(linker,"\"/manifestdependency:type='win32' \
name='Microsoft.Windows.Common-Controls' version='6.0.0.0' \
processorArchitecture='*' publicKeyToken='6595b64144ccf1df' language='*'\"")
#include <windows.h> //include all the basics
#include <tchar.h> //string and other mapping macros
#include <iostream>
#include <string>
#include "hrmcom.h"
#include "resource.h"
typedef std::basic_string<TCHAR> ustring;
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK ChildProc(HWND, UINT, WPARAM, LPARAM);
inline int ErrMsg(const ustring&);
bool CreateChild(HWND);
bool CreateChildScreen(HWND);
ustring classname = TEXT("MAINWND");
ustring childname = TEXT("CHILDWND");
HWND hwndChild[3], hwndCtrl[CTRNUM];
int WINAPI WinMain(HINSTANCE hInst, HINSTANCE, LPSTR pStr, int nCmd)
{
WNDCLASSEX wcx = { 0 };
wcx.cbSize = sizeof(WNDCLASSEX);
wcx.lpfnWndProc = WndProc;
wcx.hInstance = hInst;
wcx.hIcon = LoadIcon(hInst, MAKEINTRESOURCE(IDI_ICON1));
wcx.hCursor = reinterpret_cast<HCURSOR>(LoadImage(0, IDC_ARROW,
IMAGE_CURSOR, 0, 0, LR_SHARED));
wcx.hbrBackground = reinterpret_cast<HBRUSH>(COLOR_BTNFACE + 1);
wcx.lpszClassName = classname.c_str();
if (!RegisterClassEx(&wcx))
{
ErrMsg(_T("Failed to register wnd class"));
return -1;
}
wcx.lpfnWndProc = ChildProc;
wcx.cbWndExtra = sizeof (long);
wcx.hIcon = NULL;
wcx.lpszClassName = childname.c_str();
if (!RegisterClassEx(&wcx))
{
ErrMsg(_T("Failed to register wnd class"));
return -1;
}
HMENU hMenu = LoadMenu(hInst, MAKEINTRESOURCE(IDR_MENU));
HWND hwnd = CreateWindowEx(0,
classname.c_str(),
TEXT("Polar Loader"),
WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU,
400, 200, 600, 300,
0,
hMenu,
hInst,
0);
if (!hwnd)
{
ErrMsg(TEXT("Failed to create wnd"));
return -1;
}
ShowWindow(hwnd, nCmd);
UpdateWindow(hwnd);
MSG msg;
while (GetMessage(&msg, 0, 0, 0)>0)
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return static_cast<int>(msg.wParam);
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg)
{
case WM_CREATE:
//Create the Childwindows
if (!CreateChild(hwnd))
{
ErrMsg(TEXT("Failed to create Childwindows"));
return -1;
}
//Create controls of the Childwindows
if (!CreateChildScreen(hwnd))
{
ErrMsg(TEXT("Failed to create Conrols of Childwindows"));
return -1;
}
return 0;
case WM_COMMAND:
switch (LOWORD(wParam))
{
case IDM_Acc:
ShowWindow(hwndChild[0], SW_SHOW);
return 0;
case IDM_Con:
case IDM_Help:
case IDM_Log:
case IDM_Pol:
case IDM_Trans:
ShowWindow(hwndChild[0], SW_HIDE);
return 0;
}
case WM_DESTROY:
PostQuitMessage(0); //signal end of application
return 0;
default:
//let system deal with msg
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}
}
LRESULT CALLBACK ChildProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg)
{
case WM_CREATE:
SetWindowLong(hwnd, 0, 0);
return 0;
case WM_COMMAND:
switch (LOWORD(wParam))
{
case ID_CTRL+5:
MessageBeep(0);
return 0;
}
default:
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}
}
inline int ErrMsg(const ustring& s)
{
return MessageBox(0, s.c_str(), _T("ERROR"), MB_OK | MB_ICONEXCLAMATION);
}
bool CreateChild(HWND hwnd)
{
static int x;
for (x = 0; x < 3; x++)
{
hwndChild[x] = CreateWindowEx(0, childname.c_str(), NULL,
WS_CHILDWINDOW,
0, 0, 600, 300,
hwnd, (HMENU)x,
(HINSTANCE)GetWindowLong(hwnd, GWL_HINSTANCE),
NULL);
if (!hwndChild[x]) return FALSE;
}
return TRUE;
}
bool CreateChildScreen(HWND hwnd)
{
LPCWSTR lpType[CTRNUM] = { TEXT("static"), TEXT("edit"), TEXT("edit"), TEXT("static"), TEXT("static"), TEXT("button") };
LPCWSTR lpName[CTRNUM] = { TEXT("Log on to Gedysan Training App:"), TEXT(""), TEXT(""), TEXT("Username:"), TEXT("Password:"), TEXT("Log on") };
DWORD dStyle[CTRNUM] = { WS_CHILD | WS_VISIBLE | ES_LEFT,
WS_CHILD | WS_VISIBLE | ES_LEFT | WS_BORDER | ES_AUTOHSCROLL,
WS_CHILD | WS_VISIBLE | ES_LEFT | WS_BORDER | ES_PASSWORD | ES_AUTOHSCROLL,
WS_CHILD | WS_VISIBLE | ES_LEFT,
WS_CHILD | WS_VISIBLE | ES_LEFT,
WS_CHILD | WS_VISIBLE | ES_LEFT
};
RECT rc[CTRNUM] = { { 15, 10, 400, 25 }, { 100, 40, 150, 25 }, { 100, 70, 150, 25 }, { 15, 45, 70, 25 }, { 15, 75, 70, 25 }, { 15, 110, 70, 25 } };
int iChildNum[CTRNUM] = { 0, 0, 0, 0, 0, 0 };
static int x;
for (x = 0; x < CTRNUM; x++)
{
RECT x1 = rc[x];
hwndCtrl[x] = CreateWindowEx(0, lpType[x], lpName[x], dStyle[x],
x1.left, x1.top, x1.right, x1.bottom,
hwndChild[iChildNum[0]], (HMENU)(ID_CTRL + x),
(HINSTANCE)GetWindowLong(hwnd, GWL_HINSTANCE), 0);
if (!hwndChild[x]) return FALSE;
}
return TRUE;
}

Answer 1

With your proposed approach you will get a bunch of unrelated stuff all in the WM_PAINT handler, making a messy design. When a menu selection is made you get a message. Run code related to that menu command in that message handler.
If your UI is composed of controls then WM_PAINT is not involved at all: Those controls do their own painting. Your WM_PAINT handler should do any custom painting you need, and nothing else.