I Have a Dream - A

This is the "I Have a Dream" app, the first app you'll build for the Mobile CSP course. You'll learn that app building is a creative process. You will write code that plays Martin Luther King's "I Have a Dream" speech when the user touches the phone's screen.

Objectives:

follow an instructor-led walk-through to create the I Have a Dream app on a mobile device
navigate the App Inventor programming platform
develop your understanding of what an App Inventor program is
develop your understanding of event handlers
develop your understanding of how an app makes decisions with if-else control blocks

Technical Terminology

computational artifact - an object created by a human being that involves the use of computation in some way, for example a mobile app or a web page
hardware - the large and small physical components that make up a computers such as the computer's keyboard or its processor
software - the computer programs that make up a computer system such as the mobile apps we will be creating in this course
processor - short for microprocessor or CPU
event-driven programming - a programming approach whereby the program's behavior is controlled by writing code that responds to various events that occur, such as Button clicks
User Interface - The part of computer application through which a user interacts with a program.
UI Components - Parts of the user interface such as Buttons, Labels, etc.
User Events - Actions by the user such as button clicks.
Event Handler - A block of code that reacts to an event like a button click.
IDE - An IDE is software that provides comprehensive tools for programming such as UI design, code editing, and a way to interpret and run the program.

Getting Ready

You'll start by downloading a starter app that has the image and sound files you need but is otherwise a blank app.
Open App Inventor 2.
Click on "Projects → Import Project (.aia) from my computer"
- Then choose the file you just downloaded to your computer.
The starter app will open in App Inventor.

Navigating Among the Three Main Views

There are three main views that you will use in building apps.

1. My Projects View

The My Projects View provides you with a list of your projects. To get to this view, click on the My Projects button. Use this view to create, upload, save, delete and otherwise manage your projects. To open the IHaveADreamStarter project, just click on its name.

2. Designer View

Your project will open in the Designer View, which is used for designing the app's User Interface (UI).

Note: The Designer button is greyed out, because you are already in the Designer View.

As you can see, the Designer View contains five panels:

Palette, which contains a list of categories of various elements
Components panel, which will include the list of elements contained in your app
Media panel, which will include the list of project resources that have been uploaded
Viewer, which contains a mock-up of your app's user interface
Properties panel, which contains a list of the properties for the selected component.

Make sure you can identify each of these panels.

For the app shown here, the Screen1 component is selected in the Components panel and its properties are shown in the Properties panel. As the app designer, you can change the default values of the screen's title and other properties.

Change the screen's Title to "Speech Player"
Change the screen's ScreenOrientation to "Portrait."
Change the screen's BackgroundColor to a black

3. Blocks Editor View

The Blocks Editor View is used to create the code blocks for your apps. To navigate to the Blocks Editor View, click on the Blocks button.

The Blocks View consist of two main panels:

Blocks panel on the left, which is also known as the Toolbox
Viewer panel on the right, which is known as the Workspace

Also at the bottom left of the Blocks view, all the media files are listed.

The Blocks panel contains a list of Built-in blocks, which include blocks for doing Math, setting Colors, and other tasks. For example, if you click on "Math" you will see a drawer full with all of the various math operations that you can do in App Inventor. The Toolbox also contains a list of Component blocks. So far there is only the Screen1 component. If you click it you will see the various operations you can perform on that component.

Video Tutorial

Text steps below.

User Interface

What is the app's user interface (UI)? It is that part of the app that interacts with the user. It includes any elements that the user can see, hear or feel. Designing an attractive and easy-to-use UI is an important part of building good mobile apps.

The user interface (UI) for our I Have a Dream app will consist of four Components, a Button, a Sound, and two Labels. Remember that this is done in the Designer View.

Your Viewer panel should look like this when your app is complete.

Adding a Label Component

Drag and drop a Label component from the Palette's User Interface category to the Viewer. It will be named Label1.
Select Label1 by clicking on it in the Viewer or the Components panel.
Click on its Text property and change it to "Martin Luther King".
Add a second Label component and set its Text property to "Tap to hear the speech"

Adding a Button Component

Drag and drop a Button component from the Palette's User Interface category to the Viewer. It will be named Button1.
Select Button1 by clicking on it in the Viewer or the Components panel.
Click on its Image property and select the "mlk.jpg" image from the drop-down list.

Click on its Text property and change it to an empty string by deleting "Text for Button1".

Adding a Player (Sound) Component

Click on the Palette's Media category to open it.
Drag and drop a Player component from the Media category to the Viewer. It will be named Player1 and it will appear at the bottom of the Viewer under Screen1 as a non-visible component.
Select Player1 by clicking on it in the Viewer or the Components panel.
Click on its Source property and select the "king.mp3" sound file from the drop-down list.

Coding the App's Behavior

It's time to get the app to play the speech when we touch its screen. For this we will be using the Blocks editor. So switch now to the Blocks Editor View.

Event Driven Programming

Mobile apps use a style of programming known as event driven programming. An app's behavior depends on how the user programs the app to respond to various events. An example of an event would be when the user clicks on a button or when the phone's location changes or when a text message is received. We'll write apps that respond to all of these events.

For the I Have a Dream app, there is only one event that we care about, the Button click event.

Click on the Button1 component in the Toolbox.
Drag and drop the when Button1.Click block into the Workspace.

This is an example of a when event block, which is also called an event handler block.

Notice that it has a empty do slot. When Button1 is clicked, the app will do whatever code we put into this slot.

We want it to play Martin Luther King's speech when the button is clicked.

Click on the Player1 component in the Toolbox. This will open the Player1 drawer.
Drag and drop the call Player1.start block into the do slot. If your computer's sound is not muted, you should hear an audible 'click' as the blocks snaps into place.

To summarize, whenever the user clicks on Button1, the app will respond by playing Player1's media file. This completes the coding of the I Have a Dream app.

Still Curious?

Report abuse