Dagger is not required to use the Shell library, but it has a lot of obvious benefits:
As such, the Shell also tries to provide some reasonable out-of-the-box modules for use with Dagger.
All the Dagger related code in the Shell can be found in the com.android.wm.shell.dagger package, this is intentional as it keeps the “magic” in a single location. The explicit nature of how components in the shell are provided is as a result a bit more verbose, but it makes it easy for developers to jump into a few select files and understand how different components are provided (especially as products override components).
The module dependency tree looks a bit like:
Ideally features could be abstracted out into their own modules and included as needed by each product.
In some rare cases, there are base components that can change behavior depending on which product it runs on. If there are hooks that can be added to the component, that is the preferable approach.
The alternative is to use the @DynamicOverride annotation to allow the product module to provide an implementation that the base module can reference. This is most useful if the existence of the entire component is controlled by the product and the override implementation is optional (there is a default implementation). More details can be found in the class's javadoc.