Portées et durées de vie des composants

A scope decides how long Hilt keeps a single instance alive and where it gets shared. It is about lifetime, not just creation.

Without a scope annotation, Hilt builds a new instance every time it is requested. That is fine for cheap, stateless objects.

Hilt provides a set of components that match Android lifetimes, from the whole app down to a single view. Each owns its own instances.

SingletonComponent lives as long as the app. Bindings here with @Singleton are created once and shared across every screen.

ActivityComponent follows one Activity. Use @ActivityScoped to share an instance across that Activity and recreate it on a new one.

ViewModelComponent matches a ViewModel's life. With @ViewModelScoped a dependency is shared only within that one ViewModel.

Each scope annotation pairs with one component. @Singleton goes with SingletonComponent, @ActivityScoped with ActivityComponent, and so on.

Components nest: an Activity lives inside the app, a Fragment inside the Activity. A child can use anything its parents provide.

Scoping costs memory, because the instance is held until its component dies. Only scope objects whose state genuinely needs to be shared.

Never inject a short-lived object, like an Activity, into a Singleton. The longer-lived holder would keep it alive and leak memory. ⚠️

Match the scope to the data's life: app config in Singleton, screen state in ViewModelScoped. The right fit prevents leaks and waste.

You learned that scopes tie an instance's lifetime to a component, from Singleton down to ViewModel, so dependencies live exactly as long as needed. 🎯