LAB 4 — Navigation, ViewModel & App Architecture
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Mobile Application Development | SUZA | Semester II 2025/2026

OBJECTIVES
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- Set up Navigation-Compose with NavHost / NavController
- Pass arguments between screens
- Introduce ViewModel with StateFlow
- Apply unidirectional data flow (UDF)

SETUP
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In your app's build.gradle.kts (Module):
  implementation("androidx.navigation:navigation-compose:2.7.7")
  implementation("androidx.lifecycle:lifecycle-viewmodel-compose:2.7.0")

EXERCISES
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1. Two-Screen Hello App
   - HomeScreen: a TextField for name + "Greet" button
   - GreetingScreen: shows "Hello, <name>!" and a "Back" button
   - Pass the name as a route argument:
       navController.navigate("greeting/$name")
   - Route: "greeting/{name}"

2. Cupcake Order (simplified)
   Build an ordering flow with 4 screens:
     a. StartOrderScreen   — choose quantity (1, 6, 12)
     b. FlavorScreen       — pick flavour from radio buttons
     c. PickupScreen       — pick a date (3 options: today, tomorrow, in 3 days)
     d. SummaryScreen      — show quantity, flavour, date, price; "Send" button
                             launches a share Intent (ACTION_SEND)
   Use a single OrderViewModel holding StateFlow<OrderUiState>.
   Each screen reads/updates the shared ViewModel.

3. Scaffold + TopAppBar with Back
   In Cupcake, every screen except Start has a back arrow in the TopAppBar
   that calls navController.navigateUp().

4. Settings Sub-Flow
   - Add a "Settings" FAB on HomeScreen
   - Navigate to SettingsScreen with a theme toggle (light/dark)
   - Apply the chosen theme to the whole app (hoist to root via ViewModel)

REQUIREMENTS
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- Package structure:
    ui/       (composables, screens)
    ui/theme/
    viewmodel/
    data/     (model classes, enums)
- Every Composable screen must be previewable independently using
  hoisted parameters — do NOT call viewModel() inside the screen if it
  would prevent previews.

DISCUSSION (NOTES.md)
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- Why does Compose recommend a single-Activity architecture?
- What does "unidirectional data flow" mean in your Cupcake flow?
- How does ViewModel help with screen rotation?

DELIVERABLES
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- Project "CupcakeApp" pushed to GitHub as "mad-lab04"
- Screenshots of all 4 Cupcake screens + Settings
- NOTES.md with answers to discussion