MFC呼叫QT編寫的動態庫，如果QT dll裡面用到了一些訊息迴圈相關的介面，比如QTimer,QEventLoop等，會由於沒有QAppAplication而導致這些調用出現異常，如果DLL裡面沒有介面顯示的話，解決方法還是相對比較簡單的。主要思想是使用windows API hook函式，將MFC的訊息丟入QT去繞一圈，然後再交由MFC去處理，這樣QT便有啟用處理自己的訊息，如果本生已經是QT應用，則不做任何處理。

    static bool g_bOwnApplication = false;
    static HINSTANCE g_hInstance;

    BOOL WINAPI DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID /*lpvReserved*/
 
)
    {
    if (dwReason == DLL_PROCESS_ATTACH)
        g_hInstance = hInstance;
    if (dwReason == DLL_PROCESS_DETACH && g_bOwnApplication)
        delete qApp;
    return TRUE;
    }

    bool InitSdk()
    {
    if ( !g_bOwnApplication )
        g_bOwnApplication = CMfcApp::pluginInstance(g_hInstance);
    }
 

這裡放在InitSdk裡面去呼叫CMfcApp::pluginInstance而不在dllmain裡面去掉用，主要是防止靜態載入導致的QApplication衝突問題。

下面是CMfcApp的實現：

//.h
#pragma once
//for MFC use qt dll
//this solution from qt-solutions git-hub

#include <QCoreApplication>
#include <qnamespace.h>
#include <windef.h>

class CMfcApp
{
public:
    CMfcApp();
    ~CMfcApp();

    static
 
 LRESULT CALLBACK QtFilterProc(int nCode, WPARAM wParam, LPARAM lParam);
    static bool pluginInstance(Qt::HANDLE plugin);

private:
    static HHOOK s_hHook;
};

//.cpp
#include "MfcApp.h"
#include <WinBase.h>
#include <WinUser.h>
#include <processthreadsapi.h>


HHOOK CMfcApp::s_hHook = NULL;

LRESULT CALLBACK CMfcApp::QtFilterProc(int nCode, WPARAM wParam, LPARAM lParam)
{
    if (qApp) {
        // don't process deferred-deletes while in a modal loop
        qApp->sendPostedEvents(0, -1);
    }

    return CallNextHookEx(s_hHook, nCode, wParam, lParam);
}

CMfcApp::CMfcApp()
{
}


CMfcApp::~CMfcApp()
{
}

bool CMfcApp::pluginInstance(Qt::HANDLE plugin)
{
    if (qApp)
        return false;

    s_hHook = SetWindowsHookEx(WH_GETMESSAGE, QtFilterProc, 0, GetCurrentThreadId());
    int argc = 0;
    (void)new QCoreApplication(argc, 0);

    if (plugin) {
        char filename[MAX_PATH] = { 0 };
        if (GetModuleFileNameA((HINSTANCE)plugin, filename, MAX_PATH))
            LoadLibrary(filename);
    }
    return true;
}