MFC和QT的消息循环机制不同，所以，要让QT写的DLL可以供MFC调用，要做一点特殊的处理

#include <qmfcapp.h>  
#include <qwinwidget.h>  
#include <QtGui>  
  
#include <QtGui/QMessageBox>  
#include <windows.h>  
#include <QTextCodec>  

#include "widget.h"  
  
BOOL WINAPI DllMain( HINSTANCE hInstance, DWORD dwReason, LPVOID /*lpvReserved*/ )  
{  
    static bool ownApplication = FALSE;  
    //加入本地语言支持  
    QTextCodec::setCodecForTr(QTextCodec::codecForLocale());  
    QTextCodec::setCodecForCStrings(QTextCodec::codecForLocale());  
  
    if ( dwReason == DLL_PROCESS_ATTACH )  
    {  
  
        ownApplication = QMfcApp::pluginInstance( hInstance );  
    }  
    if ( dwReason == DLL_PROCESS_DETACH && ownApplication )  
    {  
        qApp->quit();  
        delete qApp;  
    }  
  
    return TRUE;  
}  
  
  
extern "C" __declspec(dllexport) int ShowDialog( HWND parent)  
{  
    QWinWidget win(parent, NULL, Qt::Window);  
    win.showCentered();  
    win.center();  
  
    QHBoxLayout hbox(&win);  
    Widget *widget = new Widget(&win);  
    widget->setWindowFlags(Qt::Window);  
    hbox.addWidget(widget);  
  
    win.show();  
    qApp->exec();  
}