App Inventor 2, 2nd Edition

Chapter 19. Programming Lists of Data

Figure 19-0.

As you’ve already seen, apps handle events and make decisions; such processing is fundamental to computing. But, the other fundamental part of an app is its data—the information it processes. An app’s data is rarely restricted to single memory slots such as the score of a game. More often, it consists of lists of information and complex, interrelated items that must be organized just as carefully as the app’s functionality.

In this chapter, we’ll examine the way App Inventor handles data. You’ll learn the fundamentals of programming both static information, in which the data doesn’t change, and dynamic information, in which data is entered by the end user. You’ll learn how to work with lists, and then you’ll explore a more complex data structure involving lists of lists and a multiple-choice quiz app.

Many apps process lists of data. For example, Facebook processes your list of friends and lists of status reports. A quiz app works with a list of questions and answers. A game might have a list of characters or all-time high scores.

You specify list data in App Inventor with a variable, but instead of naming a single memory cell with the variable, you name a set of related memory cells. You specify that a variable is multi-item by using either the make a list or create empty list blocks. For instance, the variable phoneNumbers ...