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Working with Hilt in AOSP

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Android brand logo (courtsey of Android Developers)
By Aayush Gupta
2 min read

Hilt is the recommended dependency injection library for Android used in most projects nowadays. Due to this, Hilt is also present in AOSP (with Dagger2). This post is a short snippet aiming to highlight how one can add Hilt support to their Android app being compiled in AOSP.

Dependencies

Add a dependency upon the hilt_android static library to add Hilt support.

You may also need to add a dependency upon the jetbrains-annotations library, as the generated classes seem to use annotations from it last time I checked.

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android_app {
    ...
    static_libs: [
        "jetbrains-annotations",
        "hilt_android"
    ],
    ...
}

Annotations

AOSP doesn’t have support for the Hilt Gradle Plugin. This requires us to use annotations without creating a dependency upon them.

This is only required for specific annotations such as HiltAndroidApp and AndroidEntryPoint. The majority of the other annotations work fine.

Example usage (without the Hilt Gradle Plugin) in Kotlin:

  • Application Class
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import android.app.Application
import dagger.hilt.android.HiltAndroidApp

@HiltAndroidApp(Application::class)
class FooApplication : Hilt_FooApplication()
  • Activity Class
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import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import dagger.hilt.android.AndroidEntryPoint
import org.calyxos.systemupdater.R

@AndroidEntryPoint(AppCompatActivity::class)
class MainActivity : Hilt_MainActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}

Remember that the annotations supported in AOSP are limited to what the hilt_android package provides. This means annotations provided by other dependencies, such as HiltWorker (for WorkManager), are absent. For them, prefer using factory methods such as WorkerFactory (for WorkManager) instead. Check the source for an updated list of supported annotations.

Gradle

While supporting AOSP is excellent, using annotations as shown above (without the Gradle plugin) breaks Gradle builds. To mitigate this, disable Hilt’s aggregating task in your app’s build.gradle file.

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hilt {
    enableAggregatingTask = false
}

It is recommended to use KSP instead of KAPT. KAPT is known to have issues and requires enabling correctErrorTypes.

That should be all that one may need to start working with Hilt for projects compiled in AOSP.

Engineering
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This post is licensed under CC BY 4.0 by the author.