Computer Science
Grade 9
20 min
10. Project: Building a Simple Mobile App
Apply the concepts learned in this chapter to build a simple mobile app from scratch.
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Introduction & Learning Objectives
Learning Objectives
Design a simple user interface (UI) for a mobile application using components like buttons and labels.
Implement event-driven programming by creating event handlers for user actions (e.g., a button click).
Use variables to store and update data within their application, such as a score or counter.
Integrate non-visible components, like a sound player, and trigger them with UI events.
Modify component properties (e.g., text, color, size) both in the designer and programmatically.
Package and test their application on a mobile device or emulator.
Ever wanted to create your own app, just like the ones on your phone? 📱 Let's build one from scratch, right now!
This project is your first step into the world of mobile app development. You will learn how t...
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Key Concepts & Vocabulary
TermDefinitionExample
User Interface (UI) ComponentA pre-built visual element that users can see and interact with on the screen.A Button, a Label to display text, or a TextBox for user input are all UI components.
EventAn action that occurs in the app, usually initiated by the user.A user clicking a button, shaking the phone, or the app's screen loading are all events.
Event HandlerA block of code that is written to run in response to a specific event.A `When Button1.Click` block is an event handler that contains the code to execute only when Button1 is clicked.
Component PropertiesThe settings or characteristics of a component that can be changed, such as its color, size, or the text it displays.Setting a Label's `Text` property to 'Hello, World!' or changing a Butto...
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Core Syntax & Patterns
The Event-Driven Programming Model
When [Event] happens, Do [Action]
This is the fundamental pattern for interactive apps. The app waits for a user action (the event) and then executes the specific code you've placed inside the corresponding event handler block (the action).
Setting a Property
Set [Component].[Property] to [Value]
To change a component's characteristic programmatically, you use a 'set' block. You specify which component, which property of that component, and the new value you want it to have.
Using a Variable
1. Initialize variable [name] to [initial value]. 2. Get variable [name]. 3. Set variable [name] to [new value].
Variables must first be created and given a starting value (initialization). You can then 'get' the cu...
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Challenging
You are building an app where the first click on a button shows 'Hello' and the second click shows 'Goodbye'. All clicks after the second should do nothing. Which combination of programming concepts is essential to create this logic?
A.counter variable and conditional logic (if/else if) inside the button's event handler.
B.Two separate buttons, one for 'Hello' and one for 'Goodbye'.
C.non-visible timer component that changes the text automatically.
D.Only an event handler with two `Set Label.Text` blocks.
Challenging
An app has a `score` variable, a `ScoreLabel`, a `ClickButton`, and a `PointSound`. The goal is: when `ClickButton` is pressed, increment the `score`, update `ScoreLabel` to show the new score, and play `PointSound`. What is the correct sequence of blocks inside the `When ClickButton.Click` handler?
A.1. Play Sound. 2. Set Label Text. 3. Set score variable.
B.1. Set score variable. 2. Set Label Text. 3. Play Sound.
C.1. Set Label Text. 2. Set score variable. 3. Play Sound.
D.1. Play Sound. 2. Set score variable. 3. Set Label Text.
Challenging
To best prevent the 'confusing text and numbers' pitfall in a click counter app, what is the most robust and correct practice?
A.Always convert the label's text to a number before adding 1.
B.Use two labels: one for text and one for the number.
C.Maintain a separate numeric variable for the count, perform all math on that variable, and only use the result to update the label's Text property.
D.Name the label 'Label_Number_1' so the program knows it contains a number.
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Start Practicing FreeMore from V. Mobile App Development: Building Applications for Mobile Devices
1. Introduction to Mobile App Development: Platforms, Frameworks, and Tools
2. Mobile UI/UX Design: Principles and Best Practices
5. Handling User Input: Text Fields, Buttons, and Touch Events
6. Navigation: Implementing App Navigation with React Navigation
7. Data Storage: Local Storage and AsyncStorage