Win32 API获取外部Qt应用窗口属性的实现方法咨询

Hey Kay, let's walk through how to make your Win32 API code work with that external Qt app—there are a few Qt-specific quirks to watch out for!

First, let's break down the issues in your current code and fix them step by step:

1. Qt Menus Are Often Non-Native #

Your code uses GetMenu(hMainWnd) to grab the window's menu, but Qt almost always uses its own custom menu implementation (QMenu) instead of the standard Win32 menu. That means GetMenu will likely return NULL for most Qt apps.

What to Do Instead #

If you just need to trigger a menu action, sending the corresponding shortcut command is far more reliable:

// Example: Send a Ctrl+O (File > Open) command (replace ID_FILE_OPEN with the actual command ID)
SendMessage(hMainWnd, WM_COMMAND, MAKEWPARAM(ID_FILE_OPEN, 0), 0);

To find the correct command ID, use a tool like Spy++ (included with Visual Studio) to monitor the WM_COMMAND message sent when you manually click the menu item. The wParam value will be your target command ID.

If you absolutely need to read menu text and the app does use a native menu (rare for modern Qt apps), switch to the wide-character version of GetMenuString to match Qt's Unicode support:

WCHAR strMenuText[128];
GetMenuStringW(hMenu, 0, strMenuText, 127, MF_BYPOSITION);

2. Finding Qt Child Windows #

Your FindWindowEx(hMainWnd, NULL, NULL, NULL) will grab the first child window, but Qt's main window hierarchy uses custom class names (not generic ones). You'll need to identify the correct child window class first.

Step 1: Use Spy++ to Inspect the Window #

Open Spy++, find your Qt app's main window, and expand its child windows. You'll see class names like Qt5QWindowIcon (for the titlebar icon) or QWidget (for the main content area).

Step 2: Target the Correct Child #

Use the wide-character FindWindowExW function with the specific class name:

// Replace L"QWidget" with the actual class name from Spy++
HWND hChildWnd = FindWindowExW(hMainWnd, NULL, L"QWidget", NULL);

3. Full Revised Code Example #

Here's a cleaned-up version of your code with Qt-specific fixes:

#include <windows.h>
#include <tchar.h>

int main() {
    // Find the Qt main window (use wide-character to match Qt's Unicode)
    HWND hMainWnd = FindWindowW(NULL, L"QT Window App");
    if (!hMainWnd) {
        MessageBoxW(NULL, L"Could not find target Qt window", L"Error", MB_OK);
        return 1;
    }

    // Attempt to get native menu (only works if Qt uses native menus)
    HMENU hMenu = GetMenu(hMainWnd);
    if (hMenu) {
        WCHAR strMenuText[128];
        GetMenuStringW(hMenu, 0, strMenuText, 127, MF_BYPOSITION);
        MessageBoxW(NULL, strMenuText, L"Menu Item Text", MB_OK);
    } else {
        MessageBoxW(NULL, L"Qt uses a custom menu (GetMenu won't work)", L"Note", MB_OK);
        // Uncomment below to send a menu command instead
        // SendMessage(hMainWnd, WM_COMMAND, MAKEWPARAM(0x10001, 0), 0);
    }

    // Find the target child window (use class name from Spy++)
    HWND hChildWnd = FindWindowExW(hMainWnd, NULL, L"QWidget", NULL);
    if (hChildWnd) {
        MessageBoxW(NULL, L"Found target child window", L"Success", MB_OK);
        // Example: Send text to the child window
        // SendMessage(hChildWnd, WM_SETTEXT, 0, (LPARAM)L"Test Input");
    } else {
        MessageBoxW(NULL, L"Could not find target child window", L"Error", MB_OK);
    }

    return 0;
}

Key Notes for Qt Apps #

• Always use wide-character Win32 APIs: Qt uses Unicode by default, so functions like FindWindowW and GetMenuStringW are mandatory to avoid encoding issues.
• Spy++ is your best friend: Qt's window structure is non-standard, so you need to inspect the exact class names and messages to interact correctly.
• Deep control may require DLL injection: If you need to access internal Qt widget data (like text in a QTextEdit), simple Win32 API calls won't work. You'd need to inject a Qt-based DLL into the target app to interact with its Qt objects directly.

内容的提问来源于stack exchange，提问作者Kay