Do I have to initialise with QApplication or QCoreApplication first to access external interfaces using QtDBus? I have encountered this problem in my application, it is normal to use dbus to access the internal interface of dbus when qapplication is not initialised, but accessing the external interface will give an exception, is this a bug in qt? I tried to come here to get the answer because I didn't get the answer in the official docs of qt , please enlighten me, thank you very much!