MIT App Inventor: Components, Programming, and UI Design

MIT App Inventor

A web-based visual development environment for building Android apps using event-driven, block-based programming.

Component

A reusable app element that can be visible (UI) or invisible (service) with properties, methods, and events.

Property

A configurable attribute of a component that defines its appearance or behavior (e.g., Text, FontSize, BackgroundColor).

Event

A trigger raised by user or system action that executes attached blocks (e.g., Button.Click, Clock.Timer).

Block

A visual programming unit that represents logic and snaps together to form programs.

Designer View

Workspace for assembling and arranging UI components.

Blocks View

Workspace for implementing application logic using blocks.

Palette

Categorized panel that contains all available components to drag into the app.

Viewer

The simulated device screen used to preview the UI layout.

Components Panel

Hierarchical list of components currently in the screen.

Properties Panel

Panel used to edit the selected component's properties.

Invisible Components

Non-visual components that run background tasks (e.g., Clock, TinyDB, Web).

User Interface Category

Palette group for visible widgets like Button, Label, TextBox.

Layout Category

Palette group for arranging UI using Horizontal/Vertical arrangements.

Media Category

Palette group for multimedia features like Camera, Player, Sound.

Drawing Category

Palette group for graphics like Canvas and ImageSprite.

Sensors Category

Palette group for device sensors like Accelerometer and OrientationSensor.

Storage Category

Palette group for data persistence like TinyDB and File.

Connectivity Category

Palette group for networking like Web, Bluetooth.

Social Category

Palette group for messaging features like Texting.

Accelerometer

Sensor that detects device acceleration along axes.

Clock

Non-visible component that triggers time-based events.

TinyDB

Local key-value storage for persisting small data on device.

Web

Component used to send HTTP requests and receive responses.

BluetoothClient

Component for connecting to Bluetooth devices as a client.

AI Companion

Mobile app used to test projects in real time via QR or code.

Projects Menu

Menu for creating, opening, saving, and managing projects.

Connect Menu

Menu for testing apps via AI Companion, Emulator, or USB.

Build Menu

Menu for compiling the project into an APK or AAB file.

Settings Menu

Menu for environment and editor preferences.

Event-Driven Programming

Paradigm where code runs in response to events.

If Block

Control block used to execute code conditionally.

If-Else Block

Control block with alternate execution path.

Variable

A named storage location for values used in logic.

Global Variable

A variable accessible across the entire screen.

Local Variable

A variable scoped within a specific block.

List

A collection of items managed with list blocks.

Math Block

Block category for arithmetic and numeric operations.

Text Block

Block category for string manipulation.

Procedure

Reusable block (function) that can take parameters.

Parameter

Input passed into a procedure.

Screen

A page in the app; multiple screens can exist.

Open Another Screen

Block used to navigate to another screen.

Close Screen

Block used to return to the previous screen.

Set Property

Block used to update a component's property at runtime.

Get Property

Block used to read a component's property.

when Button.Click

Event block triggered when a button is tapped.

Clock.Timer

Event block triggered at a specified interval.

Do It

Debug feature to evaluate a block in the workspace.

Error Message

Runtime or compile-time feedback indicating issues.

APK

Android Package file used to install apps on devices.

AAB

Android App Bundle format for distribution on Play Store.

Emulator

Software that simulates an Android device for testing.

USB Debugging

Method to test apps directly via USB connection.

OrientationSensor

Sensor that detects device orientation.

LocationSensor

Component that provides GPS-based location.

Camera

Component to capture images using device camera.

Player

Component for audio playback.

Canvas

Drawing surface for graphics and sprites.

ImageSprite

Movable image on Canvas with coordinates.

Ball

Circular sprite used on Canvas for animations.

HorizontalArrangement

Layout component arranging children horizontally.

VerticalArrangement

Layout component arranging children vertically.

Scrollable

Property that enables scrolling on layouts/screens.

Visible

Property that shows or hides a component.

Enabled

Property that allows or disables user interaction.

FontSize

Property controlling text size.

BackgroundColor

Property controlling background color.

Width/Height

Properties defining component size.

Fill Parent

Sizing option to occupy available space.

Percent Width

Sizing using percentage of parent.

Notifier

Component for dialogs, alerts, and messages.

File

Component for reading/writing device files.

FirebaseDB

Cloud database component for real-time data sync.

ActivityStarter

Component to start external activities/apps.

Sharing

Component to share content with other apps.

BarcodeScanner

Component to scan barcodes/QR codes.

SpeechRecognizer

Component to convert speech to text.

TextToSpeech

Component to convert text to spoken audio.

Sound

Component to play short audio clips.

Image

UI component to display images.

Label

UI component to display text.

Button

UI component to trigger actions.

TextBox

UI component for user text input.

PasswordTextBox

TextBox variant that masks input.

CheckBox

UI component for boolean input.

Switch

Toggle UI component for on/off states.

Slider

UI component for selecting a value from a range.

DatePicker

UI component to select a date.

TimePicker

UI component to select a time.

ListView

UI component to display a list of items.

Spinner

Dropdown selection UI component.

Notifier.ShowAlert

Method to display brief messages.

Notifier.ShowChooseDialog

Method to display selection dialog.

TinyDB.StoreValue

Method to save a value with a tag.

TinyDB.GetValue

Method to retrieve a value by tag.

Web.Get

Method to send HTTP GET request.

Web.PostText

Method to send HTTP POST with text payload.

BluetoothClient.Connect

Method to connect to a Bluetooth device.

BluetoothClient.SendText

Method to send text over Bluetooth.