Windows API Subclassing - Win Docs Example not Working - c++

Question

I am new to Windows Api and still learning the basics. In my project I encountered a problem that requires subclassing, so I decided to find a sample code, compile it, and see how it works in practice. I have found a relatively straightforward example at the Windows Docs webpage How to Subclass a Combo Box. After creating a parent window and making a few tweaks for the code to compile, I managed to run it, but the program appears to behave as if no subclassing was done.
This is not the first time a sample code found on the webpage is not working. Am I missing something?
My WinMain routine:
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
WNDCLASSEX wc = { 0 };
wc.lpszClassName = "MyClassName";
wc.hInstance = hInstance;
wc.style = CS_HREDRAW | CS_VREDRAW;
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
wc.cbSize = sizeof(WNDCLASSEX);
wc.lpfnWndProc = ToolbarWindowProc;
RegisterClassEx(&wc)
hwndMain = CreateWindow(
"MyClassName",
"Title",
WS_POPUPWINDOW | WS_CAPTION,
0,
0,
500,
210,
nullptr,
nullptr,
hInstance,
NULL
);
ShowWindow(hwndMain, nCmdShow);
UpdateWindow(hwndMain);
MSG msg;
while (GetMessageW(&msg, NULL, 0, 0) > 0) {
TranslateMessage(&msg);
DispatchMessageW(&msg);
}
return (int)msg.wParam;
}

Answer 1

You need to know why we need to subclass controls.
Subclassing an existing control is another way to create a custom
control. The subclass procedure can alter selected behaviors of the
control by processing those messages that affect the selected
behaviors. All other messages pass to the original window procedure
for the control. For example, an application can display a small
bitmap next to the text in a read-only, single-line edit control by
subclassing the control and processing the WM_PAINT message.
Refer: Subclassing the Window Class of an Existing Control
From the link you provide, it seems that you didn't follow the tutorial to learn how to subclass controls.
But now it seems that you need a complete example to learn.
So the first step is to use the official template, see the screensnap below:
After creation, you can start with subclassing static control.
Add the following message event to the WndProc function.
case WM_CREATE:
{
hWndStatic = CreateWindowEx(0, L"Static", NULL, WS_CHILD | WS_VISIBLE | SS_LEFT, 10, 130, 200, 40, hWnd, (HMENU)IDC_OWNERDRAWBUTTON, hInst, NULL);
SetWindowSubclass(hWndStatic, &OwnerDrawButtonProc, IDC_OWNERDRAWBUTTON, 0);
return TRUE;
}
break;
Finally, add the callback function of the subclass control.
TCHAR szText[] = _T("TestString");
LRESULT CALLBACK OwnerDrawButtonProc(HWND hWnd, UINT uMsg, WPARAM wParam,
LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData)
{
switch (uMsg)
{
case WM_PAINT:
{
RECT rc;
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hWnd, &ps);
GetClientRect(hWnd, &rc);
SetTextColor(hdc, RGB(255, 0, 255));
DrawText(hdc, szText, _tcslen(szText), &rc, DT_CENTER | DT_VCENTER);
EndPaint(hWnd, &ps);
return 0;
}
case WM_NCDESTROY:
RemoveWindowSubclass(hWnd, &OwnerDrawButtonProc, 1);
break;
}
return DefSubclassProc(hWnd, uMsg, wParam, lParam);
}
Note: Don't forget to declare the newly created function
Complete example:
// Test_SetWindowSubclass.cpp : Defines the entry point for the application.
//
#include "stdafx.h"
#include "Test_SetWindowSubclass.h"
#include <commctrl.h>
#pragma comment(lib,"Comctl32.lib")
#define MAX_LOADSTRING 100
#define IDC_OWNERDRAWBUTTON 101
// Global Variables:
HINSTANCE hInst; // current instance
WCHAR szTitle[MAX_LOADSTRING]; // The title bar text
WCHAR szWindowClass[MAX_LOADSTRING]; // the main window class name
HWND hWndStatic;
// Forward declarations of functions included in this code module:
ATOM MyRegisterClass(HINSTANCE hInstance);
BOOL InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK About(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK OwnerDrawButtonProc(HWND hWnd, UINT uMsg, WPARAM wParam,
LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData);
int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
_In_opt_ HINSTANCE hPrevInstance,
_In_ LPWSTR lpCmdLine,
_In_ int nCmdShow)
{
UNREFERENCED_PARAMETER(hPrevInstance);
UNREFERENCED_PARAMETER(lpCmdLine);
// TODO: Place code here.
// Initialize global strings
LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
LoadStringW(hInstance, IDC_TESTSETWINDOWSUBCLASS, szWindowClass, MAX_LOADSTRING);
MyRegisterClass(hInstance);
// Perform application initialization:
if (!InitInstance (hInstance, nCmdShow))
{
return FALSE;
}
HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_TESTSETWINDOWSUBCLASS));
MSG msg;
// Main message loop:
while (GetMessage(&msg, nullptr, 0, 0))
{
if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
return (int) msg.wParam;
}
//
// FUNCTION: MyRegisterClass()
//
// PURPOSE: Registers the window class.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
WNDCLASSEXW wcex;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_TESTSETWINDOWSUBCLASS));
wcex.hCursor = LoadCursor(nullptr, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wcex.lpszMenuName = MAKEINTRESOURCEW(IDC_TESTSETWINDOWSUBCLASS);
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));
return RegisterClassExW(&wcex);
}
//
// FUNCTION: InitInstance(HINSTANCE, int)
//
// PURPOSE: Saves instance handle and creates main window
//
// COMMENTS:
//
// In this function, we save the instance handle in a global variable and
// create and display the main program window.
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
hInst = hInstance; // Store instance handle in our global variable
HWND hWnd = CreateWindowW(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, nullptr, nullptr, hInstance, nullptr);
if (!hWnd)
{
return FALSE;
}
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
return TRUE;
}
//
// FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
// PURPOSE: Processes messages for the main window.
//
// WM_COMMAND - process the application menu
// WM_PAINT - Paint the main window
// WM_DESTROY - post a quit message and return
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_CREATE:
{
hWndStatic = CreateWindowEx(0, L"Static", NULL, WS_CHILD | WS_VISIBLE | SS_LEFT, 10, 130, 200, 40, hWnd, (HMENU)IDC_OWNERDRAWBUTTON, hInst, NULL);
SetWindowSubclass(hWndStatic, &OwnerDrawButtonProc, IDC_OWNERDRAWBUTTON, 0);
return TRUE;
}
break;
case WM_COMMAND:
{
int wmId = LOWORD(wParam);
// Parse the menu selections:
switch (wmId)
{
case IDM_ABOUT:
DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
break;
case IDM_EXIT:
DestroyWindow(hWnd);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
}
break;
case WM_PAINT:
{
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hWnd, &ps);
// TODO: Add any drawing code that uses hdc here...
EndPaint(hWnd, &ps);
}
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
// Message handler for about box.
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
UNREFERENCED_PARAMETER(lParam);
switch (message)
{
case WM_INITDIALOG:
return (INT_PTR)TRUE;
case WM_COMMAND:
if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)
{
EndDialog(hDlg, LOWORD(wParam));
return (INT_PTR)TRUE;
}
break;
}
return (INT_PTR)FALSE;
}
TCHAR szText[] = _T("TestString");
LRESULT CALLBACK OwnerDrawButtonProc(HWND hWnd, UINT uMsg, WPARAM wParam,
LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData)
{
switch (uMsg)
{
case WM_PAINT:
{
RECT rc;
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hWnd, &ps);
GetClientRect(hWnd, &rc);
SetTextColor(hdc, RGB(255, 0, 255));
DrawText(hdc, szText, _tcslen(szText), &rc, DT_CENTER | DT_VCENTER);
EndPaint(hWnd, &ps);
return 0;
}
case WM_NCDESTROY:
RemoveWindowSubclass(hWnd, &OwnerDrawButtonProc, 1);
break;
}
return DefSubclassProc(hWnd, uMsg, wParam, lParam);
}
Debug:
After you understand the process of subclassing controls, you can review the comment Remy gave you.
Safer subclass control.