The QtDBus XML compiler is a tool that can be used to parse interface descriptions and produce static code representing those interfaces, which can then be used to make calls to remote objects or implement said interfaces.
qdbusxml2dcpp has two modes of operation, that correspond to the two possible outputs it can produce: the interface (proxy) class or the adaptor class. The latter consists of both a C++ header and a source file, which are meant to be edited and adapted to your needs.
The qdbusxml2dcpp tool is not meant to be run every time you compile your application. Instead, it's meant to be used when developing the code or when the interface changes.
The adaptor classes generated by qdbusxml2cpp are just a skeleton that must be completed. It generates, by default, calls to slots with the same name on the object the adaptor is attached to. However, you may modify those slots or the property accessor functions to suit your needs.