about the .pri files ,It's just a naming convention for junks of .pro files that are supposed
to be included using 'include(...)' in 'real' .pro files, 'real' meaning
'having a TARGET=... line'.
The .pri file contains the list of source files, header files, .ui files, and .qrc files in the project. Developers on platforms other than Windows can add or remove files to the project by editing the .pri file.