Step #6: Add Our Database to Koin

Usually, a Room database is a singleton. And, since we are using Koin, we can have Koin supply our database to other classes via dependency injection.

In ToDoApp, add this line to the koinModule declaration:

    single { ToDoDatabase.newInstance(androidContext()) }

This simply invokes our newInstance() factory function and exposes that instance as a single object. It uses an androidContext() function, supplied by Koin, to get the Application singleton and supply that as a Context to our newInstance() factory function.

However, to enable androidContext() to work in our single() call, we need to teach Koin about our ToDoApp object. To that end, modify onCreate() in ToDoApp to look like this:

  override fun onCreate() {
    super.onCreate()

    startKoin {
      androidLogger()
      androidContext(this@ToDoApp)
      modules(koinModule)
    }
  }

Now, our startKoin() call contains an androidContext() setter call, where we provide the Context to use for our androidContext() call up in koinModule.

Technically, we could bypass all of this and have our single() in koinModule use this instead of androidContext(). The downside of that approach is that if we wanted a different Context in testing, we would be unable to provide it. Basically, Koin allows us to inject the top-level Context in addition to injecting our own classes.