使用App Inventor 2轻松创建Android应用

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Figure P-1. An app that autoresponds to texts

The app is a text “answering machine.” You launch it when you’re driving and it autor-

esponds to the texts you receive.

Because the blocks are more understandable than traditional programming code,

you’re immediately drawn in, and the real-world utility gets you asking questions

like: Can I make it so the received texts are spoken aloud? Can I make it so the

response sent back could be customized? Can I write an app that lets people vote for

something by text, like on American Idol? The answer to all these questions is “yes,”

and in this book, we’ll show you how.

What Can You Do with App Inventor?

Lots of

stu!

Play

Creating apps for your phone is fun, and App Inventor promotes exploration and

discovery. Just open App Inventor in a web browser, connect your phone, and start

putting together blocks like those in the app shown in Figure P-1. You can immedi‐

ately see and interact with the app you’re building on the phone. So you’re program‐

ming, but you’re also emailing your friend to send you a text to test your app, or

you’re controlling a LEGO NXT robot with the app you just built, or you’re unplug‐

ging the phone and walking outside to see if your app is using the location sensor

correctly.

Prototype

Have an idea for an app? Instead of writing it down on a napkin or letting it float off

into the ether, build a quick prototype. Prototypes are incomplete and unrefined

working models of your idea. Expressing an idea in text is like writing a to a friend or

loved one with prose; think of an App Inventor prototype as poetry to a venture capi‐

talist. In this way, App Inventor can serve as an electronic napkin for mobile app

development.

Build apps with personal utility

In the current state of the mobile app world, we’re stuck with the apps we’re given.

Who hasn’t complained about an app and wished it could be personalized or adjusted

in some way? With App Inventor, you can build an app exactly how you want it. In

Chapter 3, you’ll build a MoleMash game that lets you score points by touching a

xiv | Preface

randomly moving mole. But instead of using the image of the mole in the tutorial,

you can customize it so that you mash a picture of your brother or sister—something

that only you might want to do, but who cares? In Chapter 8, you’ll write a quiz app

that asks questions about US Presidents, but you can easily customize it to ask ques‐

tions on any topic you want, from your favorite music to your family history.

Develop complete apps

App Inventor is not just a prototyping system or an interface designer—you can build

complete, general-purpose apps. The language provides all the fundamental pro‐

gramming building blocks like loops and conditionals, but in block form.

Teach and learn

Whether you’re at a middle school, high school, or university, App Inventor is a great

teaching and learning tool. It’s great for computer science, but is also a terrific tool for

math, physics, entrepreneurship, and just about any other discipline. The key is that

you learn by creating. Instead of memorizing formulas, you build an app to, say, find

the closest hospital (or mall!). Instead of writing an essay on Black History, you create

a multimedia quiz app with video and speeches from Martin Luther King, Jr., and

Malcolm X. We think App Inventor, and this book, can be a great tool in classes

throughout the curriculum.

Why App Inventor Works

Most people say that App Inventor is easy to use because of its visual, drag-and-drop

interface. But what does this mean? Why is App Inventor so easy to use?

You don’t have to remember and type instructions

One of the biggest sources of frustration for beginning programmers comes from

typing in code and having the computer spit back indecipherable error messages.

This frustration discourages many beginners from programming before they even get

to the more fun, logical problem solving.

You choose from a set of options

With App Inventor, the components and blocks are organized into drawers that are

readily available to you. You program by finding a block—which helps specify the

functionality you want to build—and dragging it into the program. You don’t have to

remember what the instructions are or refer to a programming manual.

Only some blocks plug in to each other

Instead of chastising programmers with cryptic error messages, App Inventor’s

blocks language restricts you from making many mistakes in the first place. For

instance, if a function block expects a number, you can’t plug in text. This doesn’t

eliminate all errors, but it sure helps.

You deal with events directly

Traditional programming languages were designed when programming was like

working with recipes, or sets of instructions. But with graphical interfaces, and

Preface | xv

especially with mobile apps where events can happen at any time (for example,

receiving a text message or phone call), most programs are not recipes, but are

instead sets of event handlers. An event handler is a way of saying, “When this hap‐

pens, the app does this.” In a traditional language like Java, you have to understand

classes, objects, and special objects called listeners to express a simple event. With

App Inventor, you can say, “When a user clicks this button...” or “When a text is

received...” by dragging out a “When” block.

What Kind of Apps Can You Build?

You can build many dierent types of apps with App Inventor. Use your imagination,

and you can create all kinds of fun, useful apps.

Games

People often begin by building games like MoleMash (Chapter 3) or apps that let you

draw funny pictures on your friend’s faces (Chapter 2). As you progress, you can

build your own versions of more complex games like Pac-Man and Space Invaders.

You can even use the phone’s sensors and move characters by tilting the phone

(Chapter 5).

Educational soware

App building is not limited to simple games. You can also build apps that inform and

educate. You can create a quiz app (Chapter 8) to help you and your classmates study

for a test, or even a create-a-quiz app (Chapter 10) that lets the users of your app cre‐

ate their own quizzes (think of all the parents that would love this one for those long

road trips!).

Location-aware apps

Because App Inventor provides access to a GPS-location sensor, you can build apps

that know where you are. You can build an app to help you remember where you

parked your car (Chapter 7), an app that shows the location of your friends or collea‐

gues at a concert or conference, or your own custom tour app of your school, work‐

place, or a museum.

High-tech apps

You can create apps that scan bar codes, talk, listen (recognize words), play music,

make music (Chapter 9), play video, detect the phone’s orientation and acceleration,

take pictures, and make phone calls. Smartphones are like Swiss Army knives for

technology, and App Inventor makes it easy to control that technology.

SMS Texting apps

No Texting While Driving (Chapter 4) is just one example of the SMS processing

apps you can build. You can also write an app that periodically texts “missing you” to

your loved ones, or an app like Broadcast Hub (Chapter 11) that helps coordinate

large events. Want an app that lets your friends vote for things by texting, like on

American Idol? You can build it with App Inventor.

xvi | Preface

Apps that control robots

Chapter 12 shows how to create an app that acts as a controller for a LEGO robot.

You can use the phone as a remote control, or you can program it to be a “brain” that

the robot carries around with it. The robot and phone communicate via Bluetooth,

and App Inventor’s Bluetooth components let you create similar apps that control

other Bluetooth devices.

Complex apps

App Inventor dramatically lowers the entrance barrier to programming and lets you

build flashy, high-tech apps within hours. But the language also provides loops, con‐

ditionals, and other programming and logic constructs necessary to build apps with

complex logic. You’ll be surprised at how fun such logic problems can be when you’re

trying to build an app.

Web-enabled apps

App Inventor also provides a way for your apps to communicate with the Web. You

can write apps that pull in data from Twitter or an RSS feed, or an Amazon Bookstore

Browser that lets you check the online cost of a book by scanning its barcode.

Who Can Build Apps?

App Inventor is freely available for anyone to use. It runs online (instead of directly

on your computer) and is accessible from any browser. You don’t even need a phone

to use it: you can test your apps on an included Android emulator. As of September

2014, there were 1.9 million registered App Inventor users from 195 countries.

Together they have created nearly ve million apps.

Who are these app builders? Were they already programmers when they started?

Some of them were, but most were not.

One of the most telling experiences has been the courses that coauthor David

Wolber teaches at the University of San Francisco. At USF, App Inventor is taught as

part of a general education computer science course targeting primarily business

and humanities students. Many students take the course because they are afraid of

math, and the course fullls the dreaded Math Core requirement. The vast majority

have never even dreamed of writing a computer program.

Despite having no prior experience, the students have been successful in learning

App Inventor and building great apps. An English major created the rst No Texting

While Driving app, two communications majors created Android, Where’s My Car?

(Chapter 7), and an International Studies major created the Broadcast Hub app

(Chapter 11). When an art major knocked on Wolber’s oce door one night well after

hours asking how to write a while loop, Wolber knew that App Inventor had dramati-

cally changed the computer science education landscape.

The media grasped the signicance as well. The New York Times called App Inventor

“Do-It-Yourself App Creation Software.” The San Francisco Chronicle reported on the

Preface | xvii

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