Qt - Create a simple theming system (changing colors of GUI)

Question

I want to be able to create an simple internal theming system for my program (by internal I mean I don't need to be able to load custom themes from user system... all themes will be embedded inside the program itself.)
I can think of some ways:

• simply put all color inside the main stylesheet of the program, every time the colors need to change, retrieve main stylesheet, parse and change the colors, and then reapply it again (or have multiple stylesheet with different colors, and apply them when its needed).
• Create a top widget that only hold the colors for each widget, and then a child widget that hold other stylesheet for other styling, and all the UI as child of this widget... in this way we need to only change the first stylesheet.
• ... (not sure about other ways, but I'm sure there is some... maybe using QStyle or something..?)

I'm not sure what is the best way to achieve what I'm after, that will be best at both performance and the code itself...
I know the first way will be heavy in performance side, to each time change the whole stylesheet and rerender the whole program. (I think at least)
the second option though, I'm not sure how it will work, I mean its any better then the first one?!
or there is any other better methods..?

Answer 1

you should create a .qss file and add it in your .qrc like you add your icons. then write all your stylesheet there. you can have multiple Style.qss files and these files are your themes and whenever you change it your theme will change.

1. add your Style.qss File in your Resources(.qrc)
2. write these codes in main.cpp

Load the application style

QFile  styleFile(":/style.qss");
styleFile.open(QFile::ReadOnly);
   

Apply the loaded stylesheet

QString  style(styleFile.readAll());
a.setStyleSheet(style);

For more information :

https://github.com/GTRONICK/QSS

https://github.com/ColinDuquesnoy/QDarkStyleSheet