book

App Inventor 2, 2nd Edition

by David Wolber, Hal Abelson, Ellen Spertus, Liz Looney

October 2014

Beginner to intermediate

360 pages

9h 3m

English

O'Reilly Media, Inc.

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Foreword
Preface
A Blocks Language for Mobile PhonesWhat Can You Do with App Inventor?Why App Inventor WorksWhat Kind of Apps Can You Build?Who Can Build Apps?Conventions Used in This BookUsing Code ExamplesSafari® Books OnlineHow to Contact UsAcknowledgments
I. AI2 Tutorials
1. HelloPurr
What You’ll LearnThe App Inventor EnvironmentDesigning the ComponentsMaking a LabelAdding the ButtonAdding the Meow SoundLive TestingAdding Behaviors to the ComponentsMaking the Kitty MeowAdding a PurrShaking the DeviceDownloading the App to Your Android DeviceSharing the AppVariationsSummary
2. PaintPot
What You’ll LearnGetting StartedDesigning the ComponentsCreating the Color ButtonsUsing Arrangements for Better LayoutsAdding the CanvasArranging the Bottom Buttons and the Camera ComponentAdding Behaviors to the ComponentsAdding the Touch Event to Draw a DotAdding the Drag Event That Draws a LineChanging the ColorLetting the User Take a PictureChanging the Dot SizeReferencing the dotSize Variable in DrawCircleChanging the Value of dotSizeThe Complete App: PaintPotVariationsSummary
3. MoleMash
What You’ll BuildWhat You’ll LearnGetting StartedDesigning the ComponentsPlacing the Action ComponentsPlacing the Label ComponentsAdding Behaviors to the ComponentsMoving the MoleCreating the MoveMole ProcedureCalling MoveMole When the App StartsCalling MoveMole every SecondKeeping ScoreProcedural AbstractionResetting the ScoreVibrating When the Mole Is TouchedThe Complete App: MoleMashVariationsSummary
4. No Texting While Driving
What You’ll LearnGetting StartedDesigning the ComponentsAdding Behaviors to the ComponentsAuto-Responding to a TextEntering a Custom ResponseStoring the Custom Response PersistentlyRetrieving the Custom Response When the App OpensSpeaking the Incoming Texts AloudAdding Location Information to the ResponseSending the Location as Part of the ResponseThe Complete App: No Texting While DrivingVariationsSummary
5. Ladybug Chase
What You’ll BuildWhat You’ll LearnDesigning the ComponentsGetting StartedPlacing the Initial ComponentsAdding Behaviors to the ComponentsMoving the LadybugDisplaying the Energy LevelStarvationAdding an AphidProgramming the Ladybug to Eat the AphidDetecting a Ladybug-Aphid CollisionThe Return of the AphidAdding a Restart ButtonAdding the FrogThe Return of the LadybugAdding Sound EffectsThe Complete App: Ladybug ChaseVariationsSummary
6. Paris Map Tour
What You’ll LearnDesigning the ComponentsSetting the Properties of ActivityStarterAdding Behaviors to the ComponentsCreating a List of DestinationsLetting the User Choose a DestinationOpening Maps with a Search URLThe Complete App: Map Tour with Activity StarterA Virtual Tour with the Web ViewerFinding the URL for Specific MapsDefining the URLs ListModifying the ListPicker.AfterPicking BehaviorThe Complete App: Map Tour (Web Viewer)VariationsSummary
7. Android, Where’s My Car?
What You’ll LearnGetting StartedDesigning the ComponentsAdding Behaviors to the ComponentsDisplaying the Current LocationRecording the Current LocationDisplaying Directions to the Remembered LocationStoring the Remembered Location PersistentlyRetrieving the Remembered Location When the App LaunchesThe Complete App: Android, Where’s My Car?VariationsSummary

8. Presidents Quiz
What You’ll LearnGetting StartedDesigning the ComponentsAdding Behaviors to the ComponentsDefining the Question and Answer ListsDefining the Index VariableDisplaying the First QuestionIterating Through the QuestionsMaking the Quiz Easy to ModifySwitching the Image for Each QuestionChecking the User’s AnswersThe Complete App: The Presidents QuizVariationsSummary
9. Xylophone
What You’ll BuildWhat You’ll LearnGetting StartedDesigning the ComponentsCreating the KeyboardCreating the First Note ButtonsAdding the Sound ComponentConnecting the Sounds to the ButtonsInstructing Android to Load the SoundsImplementing the Remaining NotesRecording and Playing Back NotesAdding the ComponentsRecording Notes and TimesPlaying Back NotesPlaying Back Notes with Proper DelaysThe Complete App: XylophoneVariationsSummary
10. MakeQuiz and TakeQuiz
What You’ll LearnGetting StartedDesigning the ComponentsAdding Behaviors to the ComponentsCreating Empty Question and Answer ListsRecording the User’s EntriesBlanking Out the Question and AnswerDisplaying Question-Answer Pairs on Multiple LinesCalling the displayQAs ProcedureSaving the QAs Persistently on the WebLoading Data from the DatabaseThe Complete App: MakeQuizTakeQuiz: An App for Taking the Quiz in the DatabaseHow the Blocks WorkThe Complete App: TakeQuizVariationsSummary
11. Broadcast Hub
What You’ll LearnGetting StartedDesigning the ComponentsAdding Behaviors to the ComponentsResponding to Incoming TextsAdding Numbers to the Broadcast ListBroadcasting the MessagesBeautifying the List DisplayLogging the Broadcasted TextsStoring the BroadcastList in a DatabaseLoading the BroadcastList from a DatabaseThe Complete App: Broadcast HubVariationsSummary
12. Robot Remote
What You’ll LearnGetting StartedDesigning the ComponentsNon-Visible ComponentsVisible ComponentsAdding Behaviors to the ComponentsConnecting to the NXTDisplaying the List of RobotsMaking the Bluetooth ConnectionDisconnecting from the NXTDriving the NXTUsing the Ultrasonic Sensor to Detect ObstaclesVariationsSummary
13. Amazon at the Bookstore
What You’ll LearnWhat is an API?Getting StartedDesigning the ComponentsProgramming the App’s BehaviorSearching by KeywordSearching by ISBNDon’t Leave Your Users HangingScanning a BookImproving the DisplayThe Complete App: Amazon at the BookstoreCustomizing the APIVariationsSummary
II. Inventor’s Manual
14. Understanding an App’s Architecture
ComponentsBehaviorAn App as a RecipeAn App as a Set of Event HandlersEvent TypesUser-Initiated EventsInitialization EventsTimer EventsAnimation EventsExternal EventsEvent Handlers Can Ask QuestionsEvent Handlers Can Repeat BlocksEvent Handlers Can Remember ThingsEvent Handlers Can Interact with the WebSummary
15. Engineering and Debugging an App
Software Engineering PrinciplesSolve Real ProblemsBuild a Prototype and Show UsersIncremental DevelopmentDesign Before CodingComment Your CodeDivide, Layer, and ConquerUnderstand Your Language: Tracking with Pen and PaperDebugging an AppWatching VariablesTesting Individual BlocksIncremental Development with Do ItDisabling BlocksSummary
16. Programming Your App’s Memory
Named Memory SlotsPropertiesDefining VariablesSetting and Getting a VariableSetting a Variable to an ExpressionIncrementing a VariableBuilding Complex ExpressionsDisplaying VariablesLocal VariablesSummary
17. Creating Animated Apps
Adding a Canvas Component to Your AppThe Canvas Coordinate SystemAnimating Objects with Timer EventsCreating MovementSpeedCollision DetectionEdgeReachedCollidingWith and NoLongerCollidingWithInteractive AnimationSpecifying Sprite Animation Without a Clock TimerSummary
18. Programming Your App to Make Decisions: Conditional Blocks
Testing Conditions with if and else if BlocksProgramming an Either/Or DecisionProgramming Conditions Within ConditionsProgramming Complex ConditionsSummary
19. Programming Lists of Data
Creating a List VariableSelecting an Item in a ListUsing an Index to Traverse a ListExample: Traversing a List of Paint ColorsCreating Input Forms and Dynamic DataDefining a Dynamic ListAdding an ItemDisplaying a ListRemoving an Item from a ListLists of ListsSummary
20. Repeating Blocks
Controlling an App’s Execution: Branching and LoopingIterating Functions on a List with for eachA Closer Look at LoopingWriting Maintainable CodeUsing for each to Display a ListThe while-do BlockUsing while-do to Compute a FormulaSummary
21. Defining Procedures and Reusing Blocks
Eliminating RedundancyDefining a ProcedureCalling a ProcedureThe Program CounterAdding Parameters to Your ProcedureReturning Values from a ProcedureReusing Blocks Among AppsThe distanceBetweenPoints ProcedureSummary
22. Working with Databases
Storing Persistent Data in TinyDBRetrieving Data from TinyDBShared Data and TinyWebDBStoring Data by Using TinyWebDBRequesting and Processing Data with TinyWebDBGetValue-GotValue in ActionA More Complex GetValue/GotValue ExampleRequesting Data with Various TagsSetting Up a Web DatabaseSummary
23. Reading and Responding to Sensors
Creating Location-Aware AppsThe Global Positioning SystemSensing Location with App InventorChecking BoundariesLocation Information Providers: GPS, WiFi, and Cell IDUsing the Orientation SensorUsing the Roll Parameter to Move an ObjectMoving in Any Direction by Using Heading and MagnitudeUsing the Phone As a CompassUsing the AccelerometerResponding to the Device ShakingUsing the AccelerometerSensor’s ReadingsDetecting Free FallSummary
24. Communicating with the Web
The WebViewer ComponentThe Web ComponentStock Market SampleTinyWebDB and TinyWebDB-Compliant APIsSummary
Index

Content preview from App Inventor 2, 2nd Edition

Chapter 7. Android, Where’s My Car?

You parked as close to the stadium as you possibly could, but when the concert ends, you don’t have a clue where your car is. Your friends are equally clueless. Fortunately, you haven’t lost your Android phone, which never forgets anything, and you remember you have the hot new app, Android, Where’s My Car? With this app, you click a button when you park your car, and the Android uses its location sensor to record the car’s GPS coordinates and address. Later, when you reopen the app, it gives you directions from where you currently are to the saved location—problem solved!

What You’ll Learn

This app covers the following concepts:

Determining the location of the Android device by using the LocationSensor component.
Persistently recording data in a database directly on the device by using TinyDB.
Using the WebViewer component to open Google Maps from your app and show directions from one location to another.

Getting Started

Connect to the App Inventor website and start a new project. Since project names can’t have spaces, name it “AndroidWhere”. Set the screen’s title to “Android, Where’s My Car?” Connect your device or emulator for live testing.

Designing the Components

The user interface for Android, Where’s My Car? consists of labels to show your current and remembered locations, and buttons to record a location and show directions to ...

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