[Hilt] Question: How to create a subcomponent of a custom component that has a Builder

We’re using Hilt in version 2.34.1-beta.

We have 2 components:

@LoggedUserScope
@DefineComponent(parent = SingletonComponent::class)
interface UserComponent {

    @DefineComponent.Builder
    interface Builder {
        fun setUser(@BindsInstance user: User): Builder
        fun setToken(@BindsInstance string: String): Builder
        fun build(): UserComponent
    }
}

@ProjectScope
@DefineComponent(parent = UserComponent::class)
interface ProjectComponent {

    @DefineComponent.Builder
    interface Builder {
        fun setProject(@BindsInstance project: Project): Builder
        fun build(): ProjectComponent 
    }
}

The UserComponent, without ProjectComponent works fine. We are able to get the instance using EntryPoint. Also, when the ProjectComponent has a parent set to SingletonComponent, everything is OK. But we’d like to have them nested. A logged user can choose a project, but after logging out projects are not available.

With the above code the compiler screams that we need @Provide-annotated method for the ProjectComponent.Builder. As I understand it correctly, the ProjectComponent needs to know the instance of UserComponent to be initialized. How can it be provided? All samples we found are using a parent component without any parameters, so the compiler can instantiate it automagically.

CC: @roshanrajaratnam

[Chang-Eric]

There is one last thing I noticed that, ProjectDataRepository did not needed to be scoped with @ProjectScope (but still scoped it and seems like it had no effect of not being scoped?).

A scope annotation just tells you whether or not the object should be cached. If you don’t scope it, every time you ask for a ProjectDataRepository you’ll get a new instance. This doesn’t affect the parent/child relationship of UserComponent and ProjectComponent. (Note that it is really the components that have the relationship. I think it gets confusing because colloquially people will often use the scope and component names interchangeably to mean the same thing, but most of the time it is technically the components you should be referring to as the scope annotation really just controls caching within that component).

Anyway, closing this now since it seems everything has been solved.

[Chang-Eric]

because it’s also the parent of the ProjectComponent

Not sure I followed that, but the Builder isn’t the parent of the ProjectComponent? Or do you mean that because UserComponent is the parent, the child ProjectComponent should be able to be injected the same as the parent?

In any case, you would need something like the following:

// This doesn't really have to be scoped, but it probably is best for it to be, especially if you
// presumably will be storing the ProjectComponent instances in this class.
@LoggedUserScope
public final class UserFoo {
  @Inject UserFoo(ProjectComponent.Builder builder) { ... }
}

// Somewhere where you have your UserManager
UserFoo userFoo = userManager.userComponent().getUserFoo();
userFoo.buildProjectComponent();

The requirement is that the code that injects the ProjectComponent.Builder has to be injected from the parent UserComponent. If it is injected from somewhere else, like the Hilt ViewModelComponent, then it won’t work. The reason injecting the UserComponent.Builder works is because the parent is the Hilt SingletonComponent, so the parent is accessible from the ViewModelComponent since ViewModelComponent is a child of SingletonComponent. ViewModelComponent is not a child of UserComponent however so that is why it does not work for ProjectComponent.Builder.