Simple cross platform in app purchase plugin for Xamarin.iOS and Xamarin.Android

• Please use test NuGet feed: https://ci.appveyor.com/nuget/inappbillingplugin

• Available on NuGet in Future: https://www.nuget.org/packages/Plugin.InAppBilling

• Install into your PCL project and Client projects.

Build status:

Platform Support

You must have your IAP setup before testing the code:

try
{
    var productId = "mysku";

    var connected = await CrossInAppBilling.Current.ConnectAsync();

    if (!connected)
    {
        //Couldn't connect
        return;
    }

    //try to purchase item
    var purchase = await CrossInAppBilling.Current.PurchaseAsync(productId, ItemType.InAppPurchase, "apppayload");
	if(purchase == null)
	{
		//Not purchased
	}
	else
	{
		//Purchased!
	}
}
catch (Exception ex)
{

}
finally
{
    busy = false;
    await CrossInAppBilling.Current.DisconnectAsync();
}

You can easily check the status of any number of skus by scanning the purchased items for the app/user.

try
{ 
	var productId = "mysku";
    var connected = await CrossInAppBilling.Current.ConnectAsync();

    if (!connected)
    {
        //Couldn't connect
        return;
    }

    //check purchases

    var purchases = await CrossInAppBilling.Current.GetPurchasesAsync(ItemType.InAppPurchase);

    if(purchases?.Any(p => p.ProductId == productId) ?? false)
    {
        //Purchase restored
    }
    else
    {
        //no purchases found
    }
    
    await CrossInAppBilling.Current.DisconnectAsync();
}
catch (Exception ex)
{
    //Something has gone wrong
}
finally
{
    busy = false;
}

This is helpful to get translated pricing to display to your users.

• Read the iOS developer In App Purchases API Docs
• Read all parts of the setup from Xamarin documentation, which are great.
• You must setup an in app purchase and understand what each of them are.
• Read through the testing documentation

It is important to follow these steps for Android:

Prerequisite

• Read the Android developer In App Billing API Docs
• Ensure app is on app store and In App Purchase is setup
• You must place this code in your Main/Base Activity where you will be requesting purchases from.

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
    base.OnActivityResult(requestCode, resultCode, data);
    InAppBillingImplementation.HandleActivityResult(requestCode, resultCode, data);
}

I recommend reading the Google Play services Security and Design that will walk you through your options on storing your public key. InAppBilling Pluging offers Android developers an additional interface, IInAppBillingVerifyPurchase to implement to verify the purchase with their public key and helper methods to encrypt and decrypt. It is recommended to atleast follow the XOR guidance if you do not want to setup a verification server.

IInAppBillingVerifyPurchase has 1 Method: Task VerifyPurchase(string signedData, string signature). It returns a boolean that validates that the signed data and signature match based on the public key. If you pass in null to the purchase or get purchases methods no verification will be done.

The simplest and easiest (not necessarily the most secure) way is to do the following:

• Take your public key and break into 3 parts
• Run each through the helper XOR method: Plugin.InAppBilling.InAppBillingImplementation.InAppBillingSecurity.TransformString
• Save each value out and put them in your app
• Implement the interface with this funcationality:

    public class Verify : IInAppBillingVerifyPurchase
    {
        const string key1 = @"XOR_key1";
        const string key2 = @"XOR_key2";
        const string key3 = @"XOR_key3";

        public Task<bool> VerifyPurchase(string signedData, string signature)
        {

#if __ANDROID__
            var key1Transform = Plugin.InAppBilling.InAppBillingImplementation.InAppBillingSecurity.TransformString(key1, 1);
            var key2Transform = Plugin.InAppBilling.InAppBillingImplementation.InAppBillingSecurity.TransformString(key2, 2);
            var key3Transform = Plugin.InAppBilling.InAppBillingImplementation.InAppBillingSecurity.TransformString(key3, 3);
            
            return Task.FromResult(Plugin.InAppBilling.InAppBillingImplementation.InAppBillingSecurity.VerifyPurchase(key1Transform + key2Transform + key3Transform, signedData, signature));
#else
            return Task.FromResult(true);
#endif
        }
    }

Plugin.InAppBilling.InAppBillingImplementation.InAppBillingSecurity.VerifyPurchase takes in your public key which you now have reversed back to standard and will do proper RSA validation on the signed data.

• Ensure you have app in Alpha/Beta with the NuGet installed. This will add "com.android.vending.BILLING" permission for you
• Create an IAB product, make sure it is published and active
• Add a test account to the app, ensure it is the main account on device, and that account is opted-in as tester
• Validated your version code and number in your development environment match what is in the Play store.
• You MUST sign the APK even in debug mode. In XS this is in the properties. In VS you must manually add this to your project:

<AndroidKeyStore>True</AndroidKeyStore>
<AndroidSigningKeyStore>KeystoreLocation</AndroidSigningKeyStore>
<AndroidSigningStorePass>PASS</AndroidSigningStorePass>
<AndroidSigningKeyAlias>ALIAS</AndroidSigningKeyAlias>
<AndroidSigningKeyPass>PASS</AndroidSigningKeyPass>

• If you see "You need to sign into your google account". This most likely means that you don't have an items published and active for IAB
• If you see "This version of the application is not configured for billing through Google Play": This means the versions number don't match or you don't have the app configured to sign correctly with your keystore.
• If you see "The publisher cannot purchase this item": This means you are trying to buy it on your developer account, and that isn't allowed, you need a different account.

• Read the UWP developer In App Purchases API Docs
• You must setup an in app purchase
• Read through the testing documentation

In UWP, in-app purchases get can be tested by using the CurrentAppSimulator class instead of CurrentApp. To switch the UWP's InAppBillingImplementation to testing mode, set the testingMode boolean in the constructor.

IInAppBilling inAppBilling = new InAppBillingImplementation(true);

Under MIT, see LICENSE file.