If you ever need a QApplication mainloop in a DLL u can use following header concept for your DLL.

dllmain.cpp

static QApplication* app;
static int argc = 0;

BOOL APIENTRY DllMain(HMODULE hModule, DWORD reason, LPVOID lpReserved)
{
    switch (reason)
    {
        case DLL_PROCESS_ATTACH:
        {
            app = new QApplication(argc, NULL);
            break;
        }

        case DLL_PROCESS_DETACH:
        {
            delete app;
            break;
        }
    }
    return(TRUE);
}