How to inject application context in a repository with Hilt?

Question

I want to inject an application context into a repository class to create a room database instance inside the repository. I am using Hilt for dependency injection.

Can we use hilt for passing application context or do I have to manually pass it?

I am getting the following error:

[Dagger/MissingBinding] android.content.Context cannot be provided without an
@Provides-annotated method. public abstract static class ApplicationC 
implements ExartApplication_GeneratedInjector

Solution

Just use @ApplicationContext annotation on your context parameter.

By annotating context with @ApplicationContext provided by Hilt, we don't need to create a provider for the application context.

import dagger.hilt.android.qualifiers.ApplicationContext

/* For hilt versions lower than v2.28.2 use ApplicationComponent instead of
SingletonComponent. ApplicationComponent is deprecated and even removed in 
some versions above v2.28.2 so better refactor it to SingletonComponent. */


@Module
@InstallIn(SingletonComponent::class)
class ProductionModule {

    @Singleton
    @Provides
    fun provideAppDatabase(@ApplicationContext appContext: Context): AppDatabase {
        return Room
            .databaseBuilder(appContext, AppDatabase::class.java, AppDatabase.DB_NAME)
            .build()
    }
}

NOTE: In case you are tempted to pass activity context as a dependency, try to use application context or rethink your use-case. Passing activity context may lead to serious implications like memory leaks. Having said that, if you know what you are doing, use @ActivityContext annotation for passing the activity context. A possible use-case might be adapters.

Comments

[Arul]

Is there any way to annotate ActivityContext ?

[Dimitri Leite]

Saved me the day!

[Ashu]

@ArulMani if you need activity context to be injected, maybe you are doing something wrong. ActivityContext is a fragile thing and I don't thing it is meant to be injected carelessly.

[Rissmon Suresh]

@Ashu Is there a way to do field injection of context?

[Ashu]

@RissmonSuresh can you explain your use-case? Normally you would prefer to use constructor injection.

[Rissmon Suresh]

@Ashu Just curious about the access of context(Any object) through field injection. Earlier I was using Koin for DI and field injection can be implemented like this stackoverflow.com/a/49629378/4247543

[Ashu]

@RissmonSuresh @Inject lateinit var... for field injection. For more info refer to the docs: developer.android.com/training/dependency-injection/…

[Mohd Faizan]

by default Applicationcomponent modules provide singleton scope as per developer.android.com/training/dependency-injection/… Application ApplicationComponent @Singleton

[Ashu]

@MohdFaizan I didn't exactly get what your point is. Can you clarify what it is that you are talking about?

[Tanjim ahmed]

savior of the day