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Implementing In-App Purchase on Windows Phone 8

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In-app purchases are an excellent way to increase revenue for your Windows Phone app. In this tutorial, I'll be showing you how to implement in-app purchases in a Windows Phone 8 Silverlight application.

To test your application, you'll need to create a product to test with. This means that you'll need an active Windows Phone developer account if you want to follow along.

Introduction

Windows Phone 8 provides a convenient purchase experience, reliable payouts, geo-distributed services, and product management tools to achieve meaningful commerce in your app. You can choose between in-app purchases and other payment options (for example PayPal), but in-app purchases give you more flexibility as they provide:

  • management of products using the Windows Phone developer portal
  • geo-distributed services and payouts in more than 190 countries
  • consistent purchase experience for users across all apps on the phone and proof of authenticity through secure receipts

1. Get an App ID

In the Windows Phone developer portal's dashboard, browse to the Details tab of your app and make a note of the App ID. Also grab your Publisher GUID from the developer portal. You're going to need these details later to update the application manifest file.

If you are developing a new app, then go to the dashboard and click on Submit App to start the submission process and reserve a name for your app. Save these details and you can skip submitting the XAP file for now. Just note the App ID from the App properties section.

App ID in Windows Phone Dev Portal

2. Add a Product to Your App

Under application details, there is a Products tab where you can add and manage in-app products for your app. For the purpose of this demonstration, we have created a product named Premium App

In the Windows Phone developer portal, you need to add your in-app product's properties and description. You can optionally set custom pricing in different markets for your product.  

Add in-app product

You need to fill in the properties of your in-app product as shown in the following screenshot. Remember the Product Identifier as you will need it for listing in-app products in your app.

In-app product details

Here are a few things worth remembering while adding an in-app product:

  • You can have multiple products for an app. Each product can be consumable or durable. Durable products can only be bought once.
  • Universal apps can share in-app products, letting users buy once and use anywhere. Your in-app product category can differ, but the product name and identity should match for this to work.
  • You can define custom pricing for your products in different countries.

The description section requires you to add a product title, description, and image for the in-app product as shown in the screenshot below.

App description

Note that it may take one or two hours to process your submission before the product is published.

List of in-app products for an app in Windows Phone Dev Portal

3. Update Application Manifest

It's time to update the application manifest by adding the App ID and Publisher GUID, which you copied from the Windows Phone developer portal. Using the Solution Explorer of your project, browse to Properties and locate WMAppManifest.xml.

Visual Studio assigns a random Product ID and Publisher ID when you create a new project, which you need to change by going to the Packaging tab. If you are targeting only Windows Phone 8.1, then you need to update Package.appmanifest in addition to WMAppManifest.xml.

Update product ID and publisher ID in WMAppManifest file

4. List In-App Products in Your App

The app uses the in-app purchase API available in the Windows Phone SDK to fetch products and list them. The user now has an option to purchase these products from within the app. Depending on the application you are building, you may want to list specific products in different places, but for the purpose of the demonstration let's display all the products associated with the app and handle the purchase flow.

We need an ItemsControl to hold the products. The following code snippet shows how you can define the data template of your ItemsControl and bind the products to it. Notice that the buy button is visible only if the user hasn't purchased the product. Feel free to play with the data template to make it more attractive.

The public class ProductItem stores all the information related to a particular product. There is an ObservableCollection of type ProductItem named picItems, which stores all the products.

The next step is to add a function RenderStoreItems in the code behind to list all the products for the application. This function makes an asynchronous call to LoadListingInformationAsync to render the products for the current application. The function then iterates through every product, checking its license information and adding it to the list. We bind the name, purchase status, and price to the list box, and display it to the user.

Note that you need to enter a correct App ID, Publisher ID, and Product ID before you can deploy the sample project with this tutorial.

Next, you need to add the click event handler for the buy button. The function ButtonBuyNow_Clicked initiates the purchase. The user is presented with a purchase experience that's part of the Windows Phone 8 platform. When the purchase is complete, you can enable a locked feature or let the user download additional content. This is entirely up to you.

5. After the Purchase

You can use the in-app purchase API to enumerate the licenses the user has for the products in your app when the app is launched or resumed, or after a purchase. This lets you determine whether the user already owns the product he or she licensed, or whether its fulfillment is still pending. You can also retrieve receipts for the products purchased by the user to verify if the transaction took place using the GetProductReceiptAsync function.

Check whether LicenseInformation.IsActive returns true for a product before fulfilling a purchase. However, the call to this function is resource intensive so it is advisable not to call it at app launch or resume.

When you think a product purchase has completed, first verify that a license exists for that product ID and then check to see whether IsActive is true on that license. If the license is active then the purchase should be fulfilled immediately.

A possible scenario where in-app purchases can be useful is when you want to distribute your app for free with ads and allow the user to remove them through an in-app purchase. Here's an article on implementing a "block ads" feature using the in-app purchase API. The same technique can be used to implement a trial. The advantage is that your app is listed in the free category in the store and will as a result get you more downloads.

In the case of consumable products, it's the responsibility of the app to track consumption. The CurrentApp.LicenseInformation only provides information about the license, not the state.

6. Testing In-App Purchases

If you test your app in the emulator, in-app purchases are free and no financial transactions take place. Each time you reinstall the app in the emulator, previously stored license information is cleared.

There are three main techniques for testing in-app purchases:

  • create a Dev Center beta app and add beta in-app products
  • add the mock in-app purchase mock library to your solution
  • set up an in-app purchase mock service using Microsoft Internet Information Services (IIS)

Conclusion

In this tutorial, you have learned how to list in-app products and enable an app feature when the user purchases a product. There are lots of customizations possible with in-app purchases and they can be used in a variety of scenarios.

I encourage you to go through the In-AppPurchase API overview on MSDN. It's also worth taking a look at options to test in-app purchase capabilities in your app before publishing it on the marketplace. Feel free to download the tutorial's source files to use as a reference.

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