Android Studio User Interface

Designing an Android App

• Designing apps is like constructing a building

• The Big Picture
• Follow these steps:
  • JetPack Composeable elements
  • Create an Activity (Kotlin class) for every screen
  • Code each Kotlin class with appropriate objects and actions
  • Test the application in the emulator

Using the Android User Interface

• The interface is a window on the screen of any mobile device

• Android apps run on various form factors such as smartphones, smart watches, tablets, televisions, etc.
  • Form factor refers to the screen size, configuration, or physical layout of a device

• The layout is designed with the Composable class

Resources: String

<resources>
    <string name="app_name">Your App's Name</string>
    <string name="welcome_message">Welcome to the app!</string>
    <string name="login_button">Log In</string>
    <string name="signup_button">Sign Up</string>
    <string name="error_message">An error has occurred. Please try again.</string>
    <string name="logout_message">You have been logged out.</string>

    <!-- With placeholders -->
    <string name="greeting_message">Hello, %1$s!</string>

    <!-- With formatting -->
    <string name="item_count">You have %1$d items in your cart.</string>

    <!-- Multiline -->
    <string name="terms_conditions">By using this app, you agree to our Terms &amp; Conditions.</string>

    <!-- Array example -->
    <string-array name="days_of_week">
        <item>Monday</item>
        <item>Tuesday</item>
        <item>Wednesday</item>
        <item>Thursday</item>
        <item>Friday</item>
        <item>Saturday</item>
        <item>Sunday</item>
    </string-array>

    <!-- Plurals example -->
    <plurals name="number_of_messages">
        <item quantity="one">%d new message</item>
        <item quantity="other">%d new messages</item>
    </plurals>
</resources>

Units of Measurement

Adding a File to the Resources Folder

Creating Activities

• An Activity is one of the core components of an Android application

• Each screen is considered an activity
  • The point at which the application makes contact with users

• Planning a program
  • Gather and analyse the program requirements
  • Design the user interface
  • Design the program processing objects
  • Code the program
  • Test the program

Creating Activities

• Adding a Class File

  
  
  • A class describes a group of objects and serves as a blueprint, or template, for creating those objects
  
  
  • An object is a specific, concrete instance of a class
  
  
  • When you create an object, you instantiate it; meaning you define one particular variation of the object

The Android Manifest File

• The Android Manifest file contains:
  • the name of the Java application
  • a listing of each activity
  • permissions needed to access other Android functions (like accessing the Internet)
  • the minimum level of the Android APL

• Adding an Activity to the Android Manifest
  • When applications have more than one activity, the Manifest must have an intent to navigate among multiple activities
  • An intent in Android is an abstract description of an operation to be performed

The Android Manifest File

Coding the Kotlin Activity

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
          ...
        }
    }

Moving between composables

• NavController: Handles the app's navigation and manages the back stack of composable screens.

• NavHost: Hosts the navigation graph, specifying the composable destinations.

  
  

  val navController = rememberNavController()
  NavHost(
      navController = navController,
      startDestination = "home"
  ) {
      composable("home") { HomeScreen(navController) }
      composable("details") { DetailsScreen(navController) }
  }
  

@Composable and composable

@Composable
fun MyScreen() {
    Text("Hello")
}

NavHost(navController, startDestination = "home") {
    composable("home") { HomeScreen() }
}

Resources

In Android Studio, resources (like strings, layouts, drawables, etc.) are referenced numerically because of how they are handled in the underlying Android system for efficiency and performance.

• Efficiency/Performance: The Android build system compiles all resources into a single class (R.java or R.kt) where each resource is assigned a unique integer identifier. Using integers for referencing resources allows for faster lookup during runtime compared to using text-based identifiers.

avocado_toast_1.png // Acceptable
1_Avocado-toast.png // Not Acceptable

Now do the lab!