LAB 3 — State, Input & Interactive UIs
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Mobile Application Development | SUZA | Semester II 2025/2026

OBJECTIVES
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- Use mutableStateOf + remember / rememberSaveable
- Handle TextField input with number keyboards
- Hoist state from child to parent
- Build Switch, Checkbox, and Slider controls

EXERCISES
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1. Counter App
   - Display a number that starts at 0
   - Two buttons: "+" increments, "-" decrements (not below 0)
   - A "Reset" button sets it back to 0
   - Use rememberSaveable so rotation preserves the value

2. Tip Calculator
   Inputs:
   - Bill amount (numeric TextField)
   - Tip percentage (numeric TextField, default 15)
   - Switch: "Round up tip"
   Output:
   - Calculated tip (2 decimal places)
   - Total to pay
   Use state hoisting so the TipCalculator composable is reusable.

3. Name Badge Generator
   - TextField for first name
   - TextField for last name
   - Slider (0..72sp) for font size
   - ColorPicker row (4 circles: red, blue, green, black) — selecting sets badge colour
   Show live preview card under the inputs.

4. Simple Login Form
   - Email TextField with email keyboard type
   - Password TextField (visualTransformation = PasswordVisualTransformation())
   - "Show password" Checkbox toggles the visual transformation
   - Login button: disabled until email contains "@" and password length >= 6
   - On click: show a Toast or update a "status" Text.

5. Todo Mini-App (in-memory)
   - TextField + "Add" button appends to a mutableStateListOf<String>
   - Each item shown in a Column with a "✕" delete button
   - Empty state text shown if the list is empty
   - Use state hoisting: TodoList(items, onAdd, onRemove)

DISCUSSION QUESTIONS (write 2-3 sentences each in a NOTES.md)
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a. What is the difference between remember and rememberSaveable?
   Give a concrete example of when each one matters.

b. Why is state hoisting valuable? Name a concrete benefit it brought
   to your Todo mini-app design.

c. Why do Composables need to be "idempotent" (produce the same UI
   for the same inputs)? What breaks if they aren't?

DELIVERABLES
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- Project "StateLab" with all 5 exercises as separate Composables
- NOTES.md with answers to discussion questions
- A short screen-recording (< 60 sec) of each app in action
- Push to GitHub: "mad-lab03"