Components in Hilt

Hi, What are components in Hilt?

Components in Hilt are like the backstage crew of your Android app. They’re tied to Android framework objects for their lifecycle and scoping. Picture this: you can install modules in these components using @Module and @InstallIn.

@Module @Installin(ActivityComponent::class)—okay, that’s a mouthful—will install the module in the Activity component. So, every time an activity or any of its children (fragment / view) needs an object from this module, it’ll get a reference to a single instance maintained for all of them in that activity.

Or, in the words of the documentation:

“For each Android class in which you can perform field injection, there’s an associated Hilt component that you can refer to in the @InstallIn annotation. Each Hilt component is responsible for injecting its bindings into the corresponding Android class.”

Differentiate between Module, Component, and Dependency Container

Before we dive deeper, let’s clear up some terminology:

• Module: Simply put, a class that defines how objects/bindings are created and provided using @Provides annotation. Modules don’t have a lifecycle of their own but can be used in various components using the @InstallIn annotation. They help organize your project by containing relevant bindings like NetworkModule or DataModule.

• Component: Components define the scope and relationships between dependencies. They provide lifecycle and scope to the modules they contain. In the context of Dagger Hilt, the term Hilt Components refers to components generated by Dagger Hilt that correspond to all the Android framework classes that can have dependencies injected into them.

• Dependency Container: In Dagger Hilt, a dependency container is created by the Dagger Hilt framework to hold instances of objects and manage their lifecycle. The dependency container is responsible for creating and managing the instances of the objects defined in modules, providing them when requested by injection targets. You don’t explicitly create a dependency container; instead, Dagger Hilt generates the necessary code during compilation.

List all the Hilt Components used as Injectors for their corresponding Android Classes

Hold onto your hats, folks. Hilt provides some nifty components to inject bindings into your favorite Android classes. Check out this handy-dandy list:

What are the lifetimes of each of those components?

Now, let’s talk about lifetimes. Hilt’s got your back here too. It automatically creates and destroys instances of generated component classes, following the lifecycle of the corresponding Android classes. Check out this neat diagram:

Up Next

There you have it, folks! Components in Dagger Hilt ensure everything runs smoothly in your Android app. From scoping to lifecycle management, they’ve got it covered. Stay tuned for the next article, where we’ll dive into dependency binding and how it works, and the different ways to do it.