Tabs and Accelerators in ATL Modeless Dialogs

// DialogMessageHook.cpp: implementation of the CDialogMessageHook class.
//
//////////////////////////////////////////////////////////////////////

#include "stdafx.h"
#include "DialogMessageHook.h"

//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////

HHOOK CDialogMessageHook::m_hHook = NULL;
THWNDCollection CDialogMessageHook::m_aWindows;

// Hook procedure for WH_GETMESSAGE hook type.
//
// This function is more or less a combination of MSDN KB articles
// Q187988 and Q216503.  See MSDN for additional details
LRESULT CALLBACK CDialogMessageHook::GetMessageProc(int nCode, WPARAM wParam, LPARAM lParam)
{
    // If this is a keystrokes message, pass it to IsDialogMessage for tab
    // and accelerator processing
    LPMSG lpMsg = (LPMSG) lParam;

    if ((nCode >= 0) &&
        PM_REMOVE == wParam &&
        (lpMsg->message >= WM_KEYFIRST && lpMsg->message <= WM_KEYLAST))
    {
        HWND hWnd, hActiveWindow = GetActiveWindow();
        THWNDCollection::iterator it = m_aWindows.begin();

        // check each window we manage to see if the message is meant for them
        while (it != m_aWindows.end())
        {
            hWnd = *it;

            if (::IsWindow(hWnd) &&
                ::IsDialogMessage(hWnd, lpMsg))
            {
                // The value returned from this hookproc is ignored, and it cannot
                // be used to tell Windows the message has been handled. To avoid
                // further processing, convert the message to WM_NULL before
                // returning.
                lpMsg->hwnd = NULL;
                lpMsg->message = WM_NULL;
                lpMsg->lParam = 0L;
                lpMsg->wParam = 0;

                break;
            }

            it++;
        }
    }

    // Passes the hook information to the next hook procedure in
    // the current hook chain.
    return ::CallNextHookEx(m_hHook, nCode, wParam, lParam);
}

HRESULT CDialogMessageHook::InstallHook(HWND hWnd)
{
    // make sure the hook is installed
    if (m_hHook == NULL)
    {
        m_hHook = ::SetWindowsHookEx(WH_GETMESSAGE,
                                     GetMessageProc,
                                     _Module.m_hInst,
                                     GetCurrentThreadId());

        // is the hook set?
        if (m_hHook == NULL)
        {
            return E_UNEXPECTED;
        }
    }

    // add the window to our list of managed windows
    if (m_aWindows.find(hWnd) == m_aWindows.end())
        m_aWindows.insert(hWnd);

    return S_OK;
}

HRESULT CDialogMessageHook::UninstallHook(HWND hWnd)
{
    HRESULT hr = S_OK;

    // was the window found?
    if (m_aWindows.erase(hWnd) == 0)
        return E_INVALIDARG;

    // is this the last window? if so, then uninstall the hook
    if (m_aWindows.size() == 0 && m_hHook)
    {
        if (!::UnhookWindowsHookEx(m_hHook))
            hr = HRESULT_FROM_WIN32(::GetLastError());

        m_hHook = NULL;
    }

    return hr;
}