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CHAPTER19ProgrammingListsofData-Appinventor
CHAPTER 19
Programming Lists of Data
As you’ve already seen, apps handle events and
make decisions; such processing is fundamen-
tal 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 complex, inter-
related 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 fun-
damentals of programming both static lists (in which the data doesn’t change) and
dynamic lists (in which the data is user-generated). Then you’ll learn how to deal with
even more complex data involving lists whose items are also lists.
Many apps process lists of data. For example, Facebook processes your list of friends.
A quiz app works with a list of questions and answers. A game might have a list of
characters or all-time high scores.
List variables work like text and number variables you’ve worked with, but instead of
the variable representing a single named memory cell, it represents a related set of
memory cells. Consider, for example, the list of phone numbers in Table 19-1.
Table 19-1. A list variable represents
a set of memory cells
111–2222
333–4444
555–6666
The elements of a list are accessed using an index. An index is a position in a list, so
index 1 of the list in Table 19-1 refers to 111–2222, index 2 refers to 333–4444, and
index 3 refers to 555–6666.
App Inventor provides blocks for creating lists, adding elements to lists, selecting a
particular item from a list, and applying operations to an entire list. Let’s start with
how we create a list.
268? Chapter?19:? Programming?Lists?of?Data
Creating a List Variable
You create a list variable in the Bl
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