App Inventor

Chapter 13. Amazon at the Bookstore

Say you’re browsing books at your favorite bookstore and want to know how much a book costs on Amazon.com. With the “Amazon at the Bookstore” app, you can scan a book or enter an ISBN, and the app will tell you the current lowest price of the book at Amazon.com. You can also search for books on a particular topic.

“Amazon at the Bookstore” demonstrates how App Inventor can be used to create apps that talk to web services (aka APIs, or application programming interfaces). This app will get data from a web service created by one of this book’s authors. By the end of this chapter, you’ll be able to create your own custom app for talking to Amazon.

The application has a simple user interface that lets the user enter keywords or a book’s ISBN (international standard book number—a 10- or 13-digit code that uniquely identifies a book) and then lists the title, ISBN, and lowest price for a new copy at Amazon. It also uses the BarcodeScanner component so the user can scan a book to trigger a search instead of entering text (technically, the scanner just inputs the book’s ISBN for you!).

What You’ll Learn

In this app (shown in Figure 13-1), you’ll learn:

• How to use a barcode scanner within an app.

• How to access a web information source (Amazon’s API) through the TinyWebDB component.

• How to process complex data returned from that web information source. In particular, ...