Presenters transform domain models to presentation models that are readily displayable on UI. This might involve assembling text from string resources, which requires access to a Context. To keep them easily unit testable, it’s best not to inject a Context directly into Presenters. Instead, you can introduce Formatters. These are small helper classes that are injected into a Presenter:
class MessagingPresenter @Inject constructor(
private val messagingFormatter: MessagingFormatter
) {
suspend fun getStatus(): String = withIOContext {
val count = messagingInteractor.getMessageCount()
messagingFormatter.formatStatus(messageCount = count)
}
}
The formatters themselves are free to depend on a Context or a Resources instance:
class MessagingFormatter @Inject constructor(
private val context: Context
) {
fun formatStatus(messageCount: Int): String {
return if (messageCount == 0) {
context.getString(R.string.status_no_messages)
} else {
context.getString(R.string.status_you_have_x_messages, messageCount)
}
}
}