BillingClient and BillingClientWrapper - circular dependency injection

Question

I have a situation where my BillingDataSource aka BillingClientWrapper needs a singleton BillingClient object, but creating the BillingClient object can't be completed without a listener that's in the BillingDataSource:

class BillingDataSource(private val client: BillingClient) {
    private val _purchases = MutableStateFlow<List<Purchase>?>(mutableListOf())
    val purchases = _purchases.asStateFlow()

    val PURCHASES_UPDATED_LISTENER = PurchasesUpdatedListener { result, purchases ->
        _purchases.value = purchases
    }
}

And the dependency injection:

@Provides
@Singleton
fun provideBillingClient(
    @ApplicationContext context: Context,
    wrapper: BillingDataSource
) : BillingClient {
    return BillingClient.newBuilder(context)
        .setListener(wrapper.PURCHASES_UPDATED_LISTENER)
        .enablePendingPurchases()
        .build()
}

@Provides
@Singleton
fun provideBillingDataSource(
    client: BillingClient
) : BillingDataSource = BillingDataSource(client)

The .setListener requirement when constructing the BillingClient is turning out to be a real headache. Of course, I can break the circular dependency by putting the listener outside of the BillingDataSource, but then I'd lose access to members (like _purchases) inside of BillingDataSource, and that's hardly ideal.

How do I solve this?

Answer 1

You can extract purchase listener (and possibly some other related methods and properties) to a separate class or object.

// instead of dependency injection 
// you can use object here for PurchaseListener
@Singleton 
class PurchaseListener @Inject constructor(){
    private val _purchases = MutableStateFlow<List<Purchase>?>(mutableListOf())
    val purchases = _purchases.asStateFlow()

    val callback = PurchasesUpdatedListener { result, purchases ->
        _purchases.value = purchases
    }
}
@Singleton
class BillingDataSource @Inject constructor(
             private val client: BillingClient, 
             val purchaseListener: PurchaseListener)

@Provides
@Singleton
fun provideBillingClient(
    @ApplicationContext context: Context,
    purchaseListener: PurchaseListener
) : BillingClient {
    return BillingClient.newBuilder(context)
        .setListener(purchaseListener)
        .enablePendingPurchases()
        .build()
}

@Provides
@Singleton
fun provideBillingDataSource(
    client: BillingClient,
    purchaseListener: PurchaseListener
) : BillingDataSource = BillingDataSource(client, purchaseListener)