Should UI frameworks have separate files for UI and application code?
Do you prefer to use UI frameworks which make a distinction between UI files and application code (e.g. Qt, GTK, Angular) or do you prefer to define the UI in the application code (e.g. Flutter, Jetpack Compose, React)?
Always separate where possible. In my experience things can end up a tangled mess really easily.
I'm a big fan of mvvm. Keeps everything separate and simple.
I prefer to define the UI in application code, because separation introduces a lot of overhead for bindings.
Nevertheless, I think it is important separate UI code from business logic.
Separating them allows you to add additional interfaces, such as command-line interfaces, APIs and web pages
depends what you mean by application code.. I'd say if your business logic is exclusively used by a ui feature the best is to keep them together. but you probably want to abstract away things like data access. I found working with a nx monorepo helps reasoning about how to structure your code.