Can someone tell me how I can prevent creating an AbstractActivity or BaseActivity in a new project and still be able to do some customizations for all activities inside the app? E.g. setting up a custom toolbar… What’s the best approach for that?

Inject toolbar provider and init it in your activity?

You could use extension functions too

Use delegates, and favor composition over inheritance

I now ended up using the ToolbarProvider solution as for this use case this made sense. Thanks. But well, I prefer the naming ToolbarHandler as you might guess