App Startup 🚀 + Hilt 🗡

Combining the two newest libraries from Jetpack to provide dependencies to Initializers

(source: https://www.pexels.com/photo/rocket-launch-space-discovery-23783/)

Initializing app start is an unexpectedly complex problem. I have already briefly raised the subject here:

Abusing Dagger with Initializers

I will address how the new App Startup library from Google’s Jetpack handles (or doesn’t handle 😉) the problem in a different blog post. This one simply describes how to bind App Startup with Hilt.

All the sample code is available here:

blipinsk/app-startup-hilt-sample

Step 1: Hilt dependencies

For the most up to date version follow the official guidelines for setting up Hilt dependencies.

Right now (when the 2.28-alpha is the newest version available) the setup is as follows:

1. In your project’s root build.gradle file:

2. In your app/build.gradle file:

Step 2: App Startup dependency

For the most up to date version follow the official guidelines for setting up App Startup library.

Right now (when the 1.0.0-alpha01 is the newest version available) setting up simply means adding this dependency:

implementation "androidx.startup:startup-runtime:1.0.0-alpha01"

Step 3: Set up Application

This means all the usual stuff:

1. Create a class that extends Application.
2. Add it in your AndroidManifest.xml (under the android:name parameter in the application tag)
3. And most importantly: mark it with the new annotation @HiltAndroidApp

@HiltAndroidApp
class HiltApplication : Application()

Step 4: Create Hilt EntryPoint for Initializers

Initializers from the App Startup library are components that are not known to the Hilt library, so you need to create a custom EntryPoint for the library:

Step 5: Set up Graph Dependency Initializer

Truth be told, this step is optional. ApplicationComponent is initialized by Hilt library lazily in the Application class. It happens on the first access to the component or in the onCreate callback.

TLDR: this is not mandatory, but makes things well organized (other Initializers depend on the DependencyGraphInitializer).

Step 6: Set up your Initializers that depend on Hilt dependencies

1. Create your Initializer class:

As you can see it depends on the DependencyGraphInitializer so it will be created after it.

2. Add an inject method in the EntryPoint :

3. Register the Initializer in the AndroidManifest:

Side note to Google devs: registering in AndroidManifest should be happening automatically… Can’t we simply have a plugin or something that will generate those records for all Initializer classes?

Step 7: Enjoy dependencies being injected into your Initializers 🎉