c++ - 为什么我在使用 WS_EX_CONTEXTHELP 时看不到问号？

Question

我正在学习 WinAPI。 MSDN :

WS_EX_CONTEXTHELP

The title bar of the window includes a question mark. When the user clicks the question mark, the cursor changes to a question mark with a pointer. If the user then clicks a child window, the child receives a WM_HELP message. The child window should pass the message to the parent window procedure, which should call the WinHelp function using the HELP_WM_HELP command. The Help application displays a pop-up window that typically contains help for the child window.

WS_EX_CONTEXTHELP cannot be used with the WS_MAXIMIZEBOX or WS_MINIMIZEBOX styles.

当我尝试在我的代码中使用 WS_EX_CONTEXTHELP 时，我没有看到问号。我没有在我的代码中指向 WS_MAXIMIZEBOX 或 WS_MINIMIZEBOX 值:

为什么会这样？我的“Hello World”代码:

#include <Windows.h>
#include <tchar.h>
#include <iostream>
#include <exception>

using namespace std;

#define APP_RC_SUCCEEDED 0
#define APP_RC_UNHANDLED_EXCEPTION 1
#define APP_RC_UNKNOWN_ERROR 2
#define APP_RC_WINDOW_CLASS_WAS_NOT_REGISTERED 3

#ifdef UNICODE
#define TCOUT std::wcout
#define TCIN std::wcin
#define TCERR std::wcerr
#else
#define TCOUT std::cout
#define TCIN std::cin
#define TCERR std::cerr
#endif

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(
    HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpszCmdLine, INT iShow)
    try {
    LPCTSTR className = _T("{AAAEB8BF-04C5-4DEA-96C1-FC14F7E66A35}");

    WNDCLASSEX wndclassex;
    ZeroMemory(&wndclassex, sizeof(wndclassex));

    wndclassex.cbSize = sizeof(wndclassex);
    wndclassex.lpszClassName = className;
    wndclassex.cbClsExtra = 0;
    wndclassex.cbWndExtra = 0;
    wndclassex.hInstance = hInstance;
    wndclassex.lpfnWndProc = WndProc;
    wndclassex.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wndclassex.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
    wndclassex.hCursor = LoadCursor(NULL, IDC_ARROW);
    wndclassex.lpszMenuName = NULL;
    wndclassex.style = CS_HREDRAW | CS_VREDRAW;
    wndclassex.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);

    ATOM wAtom = RegisterClassEx(&wndclassex);

    if (!wAtom) {
        DWORD errCode = GetLastError();
        TCERR << _T("Function: RegisterClassEx. System Error Code: ")
            << errCode << endl;
        return APP_RC_WINDOW_CLASS_WAS_NOT_REGISTERED;
    }

    HWND hwnd = CreateWindowEx(
        WS_EX_CONTEXTHELP,
        className,
        _T("This is the title text..."),
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        NULL,
        NULL,
        hInstance,
        NULL);

    ShowWindow(hwnd, iShow);
    UpdateWindow(hwnd);

    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return APP_RC_SUCCEEDED;
}
catch (exception ex)
{
    TCERR << ex.what() << endl;
    return APP_RC_UNHANDLED_EXCEPTION;
}
catch (...) {
    TCERR << _T("Unknown error.") << endl;
    return APP_RC_UNKNOWN_ERROR;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {
    HDC hdc;
    PAINTSTRUCT ps;
    RECT rect;
    switch (uMsg) {
    case WM_CREATE:
        return 0;
    case WM_PAINT:
        hdc = BeginPaint(hwnd, &ps);
        GetClientRect(hwnd, &rect);
        DrawText(hdc, _T("Hello!"), -1, &rect, DT_SINGLELINE |
            DT_CENTER | DT_VCENTER);
        EndPaint(hwnd, &ps);
        return 0;
    case WM_DESTROY:
        PostQuitMessage(APP_RC_SUCCEEDED);
        return 0;
    default:
        return DefWindowProc(hwnd, uMsg, wParam, lParam);
    }
}

Answer 1

答案可以在您问题中包含的文档引用中找到:

WS_EX_CONTEXTHELP cannot be used with the WS_MAXIMIZEBOX or WS_MINIMIZEBOX styles.

您指定了包含 WS_MAXIMIZEBOX 和 WS_MINIMIZEBOX 的窗口样式 WS_OVERLAPPEDWINDOW。