How to implement SkuDetailsResponseListener for in-app billing?

Question

I want to include in-app billing in my Android app. When reading the documentation it says to:

"specify a listener which implements the SkuDetailsResponseListener interface. You can then override onSkuDetailsResponse() which notifies the listener when the query finishes"

public class MainActivity extends AppCompatActivity implements SkuDetailsResponseListener {

Which gives:

@Override
    public void onSkuDetailsResponse(BillingResult billingResult, List<SkuDetails> skuDetailsList) {

    }

However, this is a problem because it doesn't include the listener specified in the documentation, ie.

billingClient.querySkuDetailsAsync(params.build(),
    new SkuDetailsResponseListener() {
        @Override
        public void onSkuDetailsResponse(BillingResult billingResult,
                List<SkuDetails> skuDetailsList) {
            // Process the result.
        }
    });

When including the BillingClient line and the listener there is obviously a resolve symbol error as it is outside any method, so how do you work around this?

Additionally, would you then place this block inside onCreate()?

List<String> skuList = new ArrayList<> ();
skuList.add("coins5");
SkuDetailsParams.Builder params = SkuDetailsParams.newBuilder();
params.setSkusList(skuList).setType(SkuType.INAPP);

Answer 1

As documented in Billing API documentation, you also need to implement the BillingClientStateListener as well as PurchaseUpdateListener. https://developer.android.com/google/play/billing/integrate The following code is a working example in Billing API 3.0 with Android Version Targeted SDK 28. The code is defined in a Singleton class so it can be used from multiple activities with one instance of BillingClient.

     public class ApplicationBillingClient
       {
           static ApplicationBillingClient applicationBillingClient= null;
           private static BillingClient billingClient;

          private ApplicationBillingClient() {}

          private static boolean isInitialized()
     {
    return applicationBillingClient != null && billingClient != null;
}

private static void initialize(Context applicationContext)
{
    try
    {
        if(applicationContext != null)
        {
            applicationBillingClient = new ApplicationBillingClient();
            BillingClient.Builder builder=  BillingClient.newBuilder(applicationContext);
            builder.setListener(new PurchaseActivityListener());
            builder.enablePendingPurchases();
            billingClient = builder.build();
        }

        LogUtil.info("Initializing the Billing Client");

    }
    catch (Exception ex)
    {
        LogUtil.error("Error while initializing billing client", ex);
    }

}

public static ApplicationBillingClient getInstance(Context applicationContext)
{
    if(isInitialized() == false)
    {
        initialize(applicationContext);
    }

    return  applicationBillingClient;
}

public void startConnection()
{
   billingClient.startConnection(new StateListener());
}

public boolean isReady()
{
    return billingClient.isReady();
}

public void getMonthlySubscription()
{
    try
    {
        if(billingClient.isReady())
        {
            SkuDetailsParams.Builder skuBuilder = SkuDetailsParams.newBuilder();
            skuBuilder.setType(BillingClient.SkuType.SUBS);
            skuBuilder.setSkusList(Arrays.asList(new String[]{MONTHLY_BILLING_SUBSCRIPTION_SKU}));
            SkuDetailsParams params = skuBuilder.build();
            billingClient.querySkuDetailsAsync(params, new SkuDetailsListener());
        }

    }
        catch (Exception ex)
    {
        LogUtil.error("Error while querying async SKU for Monthly Subscription", ex);
    }
  }
 }

 //In your activity
 ApplicationBillingClient appBillingClient = 
 ApplicationBillingClient.getInstance(applicationContext);
        if (appBillingClient.isReady() == false)
        {
            appBillingClient.startConnection();
        }
        else
        {
           appBillingClient.getMonthlySubscription();
        }