how to change the qml libaries path of the qt default path?

[nicker player]

Ive tested the code below.but not work.the qt qml libs only was setted to the root of the qapp could work.if I moved these files into the plugins/xml I've created ,it couldnt work.so how to get the right way.

  QmlEngine* m_Engine = NULL;
   m_Engine = qquickwidget->engine();
   QString t_app_path =  QApplication::applicationDirPath();
   if(!m_Engine->pluginPathList().contains("/plugins/xml")){
       m_Engine->addPluginPath(t_app_path+"/plugins/xml");
   }