How do you implement Dependency Injection in Android, and what are its benefits?
Instruction: Describe the concept of Dependency Injection (DI) and explain how it can be implemented in Android applications using examples such as Dagger or Hilt. Highlight the benefits of using DI in Android app development.
Updated
Official answer
Dependency injection supplies a class's collaborators from outside instead of having the class construct them. For example, a repository can accept an API client and a local store in its constructor. A test can supply fakes without initializing networking or a database. Manual constructor injection is sufficient for a small graph; a framework is optional.
Dagger generates code for a declared dependency graph at compile time. Constructor injection can provide types you own; modules provide or bind types that require explicit construction or an interface-to-implementation mapping. Components define the graph and its entry points. Generated code performs the actual construction and injection at runtime.
Hilt builds on Dagger with Android-aware components. Configure its build integration, annotate the Application with @HiltAndroidApp, and supported Android entry points such as an Activity with @AndroidEntryPoint. Use @Inject constructors where possible, @Binds for interface implementations, or @Provides for construction you cannot express with constructor injection. Install modules in the component that needs the binding.
Choose lifetimes deliberately. Installing a binding in ActivityComponent does not by itself make it a singleton. A scoped binding is shared within its matching component's lifetime; an application-scoped object must not retain an Activity merely to access context. Qualifiers distinguish multiple bindings of the same type.
DI improves explicit dependencies and test substitution when the design uses those boundaries well. Costs include generated code, build configuration, graph complexity and scope mistakes. Verify that the graph compiles and test behavior with replacement dependencies; DI does not guarantee independent modules or faster execution.