# Exit Tickets: Mobile Platforms ## Lesson 1: Google Maps SDK Fundamentals ### Question 1: Vocabulary **Question**: What is the purpose of the Google Maps SDK in mobile development? **Answer**: ✓ The Google Maps SDK allows developers to embed interactive maps in mobile apps, providing features like markers, custom styling, real-time user location tracking, and integration with Google's location services. ### Question 2: Code Understanding **Question**: What does this code accomplish? ```javascript ``` **Options**: - A) Creates a static image of a map - B) Displays an interactive map centered on San Francisco ✓ - C) Opens the native Google Maps app - D) Requests user location permission ### Question 3: Problem-Solving **Question**: How would you handle the case where a user denies location permission in your map-based app? **Answer**: ✓ Provide graceful degradation by: (1) showing a default location or city center, (2) displaying a helpful message explaining why permission is useful, (3) providing a manual search option, and (4) offering a button to re-request permission via app settings. ### Question 4: Application **Question**: Design a map feature that shows all coffee shops within 1 mile of the user's current location. **Answer**: ✓ Use expo-location to get user coordinates, query Google Places API with radius=1609 (meters in a mile) and type='cafe', then render Marker components for each result using MapView. ### Question 5: Reflection **Question**: What challenges might arise when implementing maps for users in different countries? **Answer**: ✓ Challenges include: different address formats, varying levels of map detail/coverage, language localization for place names, different privacy regulations (GDPR, etc.), and offline functionality in areas with poor connectivity. --- ## Lesson 2: Custom Markers and Overlays ### Question 1: Vocabulary **Question**: What is the difference between a Marker and a Callout in react-native-maps? **Answer**: ✓ A Marker is a pin or icon placed at specific coordinates on the map, while a Callout is a pop-up info window that appears when a user taps on a Marker, displaying additional details about that location. ### Question 2: Code Understanding **Question**: What will this code render? ```javascript NYC ``` **Options**: - A) A standard red map pin - B) A custom red circular marker with "NYC" text ✓ - C) An error (invalid syntax) - D) A callout window ### Question 3: Problem-Solving **Question**: You have 500 markers to display on the map. How would you prevent performance issues? **Answer**: ✓ Implement marker clustering using libraries like react-native-maps-super-cluster. Group nearby markers into a single cluster marker showing the count, and expand clusters when the user zooms in. Also consider viewport-based filtering to only render visible markers. ### Question 4: Application **Question**: Create a custom marker design for a restaurant rating app that shows the star rating directly on the map pin. **Answer**: ✓ Use a custom View component inside the Marker with an icon image at the bottom, and overlay a star rating component (e.g., 1-5 stars using icons or unicode ★ characters) at the top. Use conditional styling to change pin color based on rating (green for 4+, yellow for 3-4, red for below 3). ### Question 5: Reflection **Question**: When should you use custom markers versus standard pins? **Answer**: ✓ Use custom markers when: you need to convey category information (restaurant, gas station, etc.) through icons, display real-time data (prices, availability), strengthen brand identity, or improve user recognition. Use standard pins for simple location marking or when performance with many markers is critical. --- ## Lesson 3: Places API and Autocomplete ### Question 1: Vocabulary **Question**: What is the purpose of the Google Places API autocomplete feature? **Answer**: ✓ Autocomplete provides real-time search suggestions as users type, returning matching places with names, addresses, and place IDs. It improves UX by reducing typing, preventing errors, and helping users discover relevant locations quickly. ### Question 2: Code Understanding **Question**: What does the `types` parameter do in a Places API search request? ```javascript const result = await placesAPI.searchNearby({ location: { lat: 37.7749, lng: -122.4194 }, radius: 1500, types: ['restaurant', 'cafe'] }); ``` **Options**: - A) Filters results to only restaurants and cafes ✓ - B) Sorts results by type - C) Returns different data structures for each type - D) Limits the number of results ### Question 3: Problem-Solving **Question**: Your autocomplete search is making too many API requests and approaching the free tier limit. How would you optimize it? **Answer**: ✓ Implement debouncing (wait 300-500ms after user stops typing before making requests), cache recent searches locally using AsyncStorage, set a minimum character count (e.g., 3 characters) before triggering searches, and use sessionToken to reduce per-keystroke charges. ### Question 4: Application **Question**: Design a search feature that lets users find nearby parks and trails, showing distance from their current location. **Answer**: ✓ Use Places API with types=['park'] and rankBy='distance', get user location with expo-location, calculate distance using Haversine formula or Google Distance Matrix API, and display results in a FlatList sorted by distance with "X miles away" labels. ### Question 5: Reflection **Question**: Why is it important to show place photos in search results? **Answer**: ✓ Photos increase user confidence in selecting a location, help distinguish between similar-named places, provide visual context about the venue's atmosphere/quality, and significantly improve click-through rates and user satisfaction. --- ## Lesson 4: Directions and Navigation ### Question 1: Vocabulary **Question**: What is a polyline in the context of map navigation? **Answer**: ✓ A polyline is a series of connected line segments drawn on the map to represent a route or path. In directions APIs, it's typically encoded as a compressed string of latitude/longitude coordinates that visualizes the turn-by-turn route. ### Question 2: Code Understanding **Question**: What does this code accomplish? ```javascript ``` **Options**: - A) Creates two markers in San Francisco and Oakland - B) Draws a red line connecting San Francisco to Oakland ✓ - C) Calculates the distance between two points - D) Requests turn-by-turn directions ### Question 3: Problem-Solving **Question**: A user's navigation route crosses a recently closed road. How would you handle this? **Answer**: ✓ Implement real-time traffic data monitoring, use Google Directions API with `departureTime=now` to get current traffic-aware routes, enable automatic rerouting when the user deviates from the path, and display a notification suggesting an alternate route if traffic conditions change significantly. ### Question 4: Application **Question**: Build a multi-stop route optimizer for a delivery app that visits 5 locations in the most efficient order. **Answer**: ✓ Use Google Directions API with waypoints and `optimizeWaypoints=true` parameter. This returns an optimized waypoint order. Display the route with numbered markers (1-5), show estimated total time/distance, and allow users to manually adjust stop order if needed. ### Question 5: Reflection **Question**: What are the ethical considerations when providing turn-by-turn navigation in residential areas? **Answer**: ✓ Consider: privacy of residents (avoiding excessive traffic through quiet neighborhoods), pedestrian safety (routing around school zones during certain hours), environmental impact (not routing through environmentally sensitive areas), and providing options to avoid toll roads or highways for accessibility. --- ## Lesson 5: Geofencing and Location Triggers ### Question 1: Vocabulary **Question**: What is geofencing and how does it work on mobile devices? **Answer**: ✓ Geofencing is creating virtual boundaries around real-world geographic areas. When a device enters or exits these boundaries, it triggers events (notifications, actions). It uses GPS, Wi-Fi, or cellular data to monitor location in the background. ### Question 2: Code Understanding **Question**: What will happen when this geofence is triggered? ```javascript await Location.startGeofencingAsync('coffeeReminder', [ { latitude: 37.7749, longitude: -122.4194, radius: 100, notifyOnEnter: true, notifyOnExit: false } ]); ``` **Options**: - A) Notification when user exits the 100m radius - B) Notification when user enters the 100m radius ✓ - C) Notification both on enter and exit - D) Continuous location tracking ### Question 3: Problem-Solving **Question**: Your geofencing battery usage is too high. What optimization strategies would you implement? **Answer**: ✓ Use larger radius geofences (reduce precision for non-critical triggers), limit the number of active geofences (iOS max 20, Android varies), use lower accuracy location updates, implement smart wake-up intervals, and combine geofencing with activity recognition to only track when user is moving. ### Question 4: Application **Question**: Design a geofence system for a retail app that sends discount notifications when users are near any of 50 store locations. **Answer**: ✓ Don't register all 50 geofences at once (device limits). Instead, use a "two-tier" approach: monitor broader city-level regions, then dynamically register specific store geofences only when users enter a city region. Use server-side location matching for better scalability. ### Question 5: Reflection **Question**: What privacy concerns arise with background location tracking for geofencing? **Answer**: ✓ Concerns include: user awareness of always-on tracking, data security/storage of location history, potential misuse by third parties, battery drain impacting device usability, and compliance with regulations like GDPR. Always be transparent, provide opt-in controls, and minimize data collection to only what's necessary. --- ## Lesson 6: ARCore Fundamentals ### Question 1: Vocabulary **Question**: What is the purpose of plane detection in ARCore? **Answer**: ✓ Plane detection identifies flat horizontal or vertical surfaces (floors, tables, walls) in the real world using the device camera and sensors. This allows virtual objects to be realistically placed on surfaces as if they exist in the physical environment. ### Question 2: Code Understanding **Question**: What does this ARCore configuration enable? ```javascript console.log(event)} /> ``` **Options**: - A) Detects vertical walls only - B) Detects horizontal surfaces and estimates lighting conditions ✓ - C) Places objects automatically when planes are found - D) Enables cloud anchors for multi-user experiences ### Question 3: Problem-Solving **Question**: ARCore is struggling to detect planes in a user's room. What could be the issues and solutions? **Answer**: ✓ Issues: poor lighting (solution: ask user to improve lighting), lack of texture/blank walls (solution: guide user to point at textured surfaces), rapid camera movement (solution: instruct slower panning), or reflective surfaces like glass (solution: avoid mirrors/windows). Provide in-app coaching UI. ### Question 4: Application **Question**: Create an AR feature that lets users measure distances between two points in their room. **Answer**: ✓ Use ARCore hit testing to detect 3D coordinates when user taps the screen, store the first tap position as startPoint, calculate distance to second tap using 3D distance formula `sqrt((x2-x1)² + (y2-y1)² + (z2-z1)²)`, draw a virtual line between points, and display distance in feet/meters. ### Question 5: Reflection **Question**: What are the hardware requirements for ARCore, and how does this impact app accessibility? **Answer**: ✓ ARCore requires devices with specific sensors (gyroscope, accelerometer, camera) and sufficient processing power. This limits accessibility to newer Android devices (typically 2017+). Impact: need to provide fallback experiences for unsupported devices, clearly communicate requirements in app store listings, and consider progressive enhancement strategies. --- ## Lesson 7: 3D Object Placement ### Question 1: Vocabulary **Question**: What is an AR anchor and why is it important? **Answer**: ✓ An AR anchor is a fixed point in 3D space that ties virtual objects to real-world positions. As the device moves, anchors help maintain object placement accuracy by updating positions relative to detected surfaces, preventing objects from "drifting" as the AR session continues. ### Question 2: Code Understanding **Question**: What will this code do when a user taps the screen? ```javascript const handleTap = (event) => { const { x, y } = event.nativeEvent; const hitTestResult = ARView.hitTest(x, y); if (hitTestResult.length > 0) { const anchor = hitTestResult[0].anchor; placeObject(anchor.transform); } }; ``` **Options**: - A) Always places an object at the tap location - B) Places an object only if a surface is detected at tap location ✓ - C) Removes existing objects at the tap location - D) Measures the distance to the tapped point ### Question 3: Problem-Solving **Question**: Virtual furniture appears too large or too small in AR. How do you ensure proper scaling? **Answer**: ✓ Use real-world measurements: load 3D models with accurate dimensions (e.g., a chair should be ~0.5m wide), provide scale reference UI (like a virtual ruler), allow users to resize objects with pinch gestures, and display dimensions in metric/imperial units. Test with physical objects of known size. ### Question 4: Application **Question**: Design an AR furniture app that prevents users from placing couches through walls or floating in mid-air. **Answer**: ✓ Implement collision detection by: raycasting from object position to check for vertical planes (walls), validating that objects are placed on horizontal planes only, checking bounding box intersections with detected surfaces, and providing visual feedback (red outline) when placement is invalid. ### Question 5: Reflection **Question**: Why is lighting estimation important for realistic AR object rendering? **Answer**: ✓ Lighting estimation analyzes the real-world environment's light color, intensity, and direction to apply matching lighting to virtual objects. This creates realistic shadows, reflections, and color temperature, making virtual objects appear to truly belong in the physical space rather than looking artificially "pasted on." --- ## Lesson 8: AR Interaction Patterns ### Question 1: Vocabulary **Question**: What is the difference between tap-to-place and drag-to-move in AR interactions? **Answer**: ✓ Tap-to-place spawns a new object at the tapped location with a single tap, while drag-to-move repositions an existing selected object by holding and dragging across the screen, continuously updating its position based on detected surfaces. ### Question 2: Code Understanding **Question**: What gesture does this code enable? ```javascript const handlePinch = (event) => { const scale = event.nativeEvent.scale; setObjectScale(prevScale => prevScale * scale); }; ``` **Options**: - A) Rotating the object - B) Moving the object - C) Scaling the object with pinch zoom ✓ - D) Deleting the object ### Question 3: Problem-Solving **Question**: Users are accidentally deleting AR objects when they mean to rotate them. How would you improve the interaction design? **Answer**: ✓ Implement explicit deletion: require a two-step process (select object → tap trash icon), use different gesture types (e.g., swipe-up to delete vs rotate with two-finger twist), add undo/redo functionality, provide haptic feedback on delete, and show confirmation dialog for important objects. ### Question 4: Application **Question**: Create an AR color picker that lets users change the color of placed 3D objects by tapping a color swatch. **Answer**: ✓ Show a UI overlay with color swatches when an object is selected, on swatch tap update the object's material/texture color property, provide a preview of the color change, include a favorites/recently used color section, and allow custom color input via RGB/hex values. ### Question 5: Reflection **Question**: What makes an AR interaction feel "natural" vs "frustrating" for users? **Answer**: ✓ Natural interactions: mimic real-world physics (gravity, friction), provide immediate visual/haptic feedback, use familiar gestures (pinch to zoom), show affordances (glowing outlines for interactive objects), and forgive errors (undo, snap-to-grid). Frustrating: lag, imprecise controls, hidden features, or complex multi-step gestures. --- ## Lesson 9: Health Connect Integration ### Question 1: Vocabulary **Question**: What is Health Connect and how does it differ from proprietary health APIs? **Answer**: ✓ Health Connect is Android's unified health data platform that aggregates data from multiple apps (Fitbit, Samsung Health, Google Fit) into one secure repository. Unlike proprietary APIs, it provides a single interface to access diverse health data sources with user-controlled permissions. ### Question 2: Code Understanding **Question**: What data will this request return? ```javascript const result = await HealthConnect.readRecords({ recordType: 'Steps', timeRangeFilter: { startTime: new Date(Date.now() - 7 * 24 * 60 * 60 * 1000), endTime: new Date() } }); ``` **Options**: - A) Steps from the last 24 hours - B) Steps from the last 7 days ✓ - C) All step records ever recorded - D) Real-time step count ### Question 3: Problem-Solving **Question**: A user granted your app permission to read step data, but the API returns empty arrays. What could be wrong? **Answer**: ✓ Possible issues: no health apps installed that write step data (solution: prompt to install Google Fit/Samsung Health), permissions granted but data source not connected, date range filter is incorrect (future dates), or Health Connect service not enabled in Android settings. Check `hasPermissions()` and guide users through setup. ### Question 4: Application **Question**: Design a feature that compares a user's walking activity this week vs last week and shows improvement percentage. **Answer**: ✓ Query two time ranges (this week and last week), aggregate steps for each period using `reduce()`, calculate percentage change: `((thisWeek - lastWeek) / lastWeek) * 100`, display with visual indicators (green arrow up, red arrow down), and show a chart comparing daily steps for both weeks using react-native-chart-kit. ### Question 5: Reflection **Question**: What privacy considerations are unique to health data compared to other app permissions? **Answer**: ✓ Health data is highly sensitive personal information that can reveal medical conditions, lifestyle habits, and predict future health risks. Considerations: never share with third parties without explicit consent, use end-to-end encryption for storage/transmission, allow granular permission controls (steps yes, heart rate no), provide transparent data usage policies, and comply with HIPAA if applicable. --- ## Lesson 10: Step Tracking and Goals ### Question 1: Vocabulary **Question**: What is the difference between instantaneous step count and aggregate step count? **Answer**: ✓ Instantaneous (or real-time) step count shows steps taken during the current session using device pedometer sensors, while aggregate step count sums all steps from multiple sources (phone, watch, other apps) over a time period using Health Connect's historical data. ### Question 2: Code Understanding **Question**: What will this code display? ```javascript const dailyGoal = 10000; const stepsTaken = 7500; const progress = (stepsTaken / dailyGoal) * 100; {stepsTaken} / {dailyGoal} steps ({progress.toFixed(0)}%) ``` **Options**: - A) 100% progress bar - B) 75% progress bar showing "7500 / 10000 steps (75%)" ✓ - C) 25% progress bar - D) An error (division by zero) ### Question 3: Problem-Solving **Question**: Users are confused why their step count doesn't update in real-time. How would you improve the UX? **Answer**: ✓ Solutions: (1) clearly label "Last synced: X minutes ago" timestamp, (2) add a pull-to-refresh gesture to manually sync, (3) implement background polling with ExpoTaskManager every 15-30 minutes, (4) show a sync indicator when fetching new data, and (5) explain in onboarding that Health Connect syncs periodically, not continuously. ### Question 4: Application **Question**: Create a streak feature that celebrates consecutive days the user hit their 10K step goal. **Answer**: ✓ Store daily completion in AsyncStorage (date → boolean), on app open check if yesterday was completed, increment streak count if true (else reset to 1 if today's goal met), display streak count with fire emoji (🔥), award badges for milestones (7, 30, 100 days), and send encouraging notifications when streaks are at risk. ### Question 5: Reflection **Question**: Why might setting the same step goal for all users be problematic? **Answer**: ✓ Users have vastly different fitness levels, mobility limitations, lifestyles (desk job vs active job), and health conditions. A 10K goal may be unattainable for someone with chronic illness but too easy for an athlete. Better approach: personalized goals based on historical average, gradual progression, or user-selected targets with AI recommendations. --- ## Lesson 11: Workout and Activity Logging ### Question 1: Vocabulary **Question**: What is the difference between passive and active workout tracking? **Answer**: ✓ Passive tracking automatically detects activities using device sensors and activity recognition AI (e.g., Google Fit detecting you're walking), while active tracking requires the user to manually start/stop a workout session, typically recording more detailed metrics (GPS route, heart rate zones). ### Question 2: Code Understanding **Question**: What type of workout data is this code writing? ```javascript await HealthConnect.insertRecords([ { recordType: 'ExerciseSession', startTime: new Date('2025-01-15T06:00:00'), endTime: new Date('2025-01-15T06:45:00'), exerciseType: 'running', distance: 5000, // meters calories: 350 } ]); ``` **Options**: - A) A 45-minute yoga session - B) A 45-minute, 5km run burning 350 calories ✓ - C) Real-time step tracking - D) Heart rate monitoring data ### Question 3: Problem-Solving **Question**: Your workout logger is draining battery because it keeps GPS active the entire run. How would you optimize it? **Answer**: ✓ Use intelligent location sampling: high accuracy only when needed (start/end, turns), lower accuracy for straight paths, pause GPS when device is stationary (detected via accelerometer), batch location updates, use Activity Recognition API to detect when workout actually starts/stops, and allow users to choose accuracy level. ### Question 4: Application **Question**: Build a running app that detects when the user stops at traffic lights and auto-pauses the workout timer. **Answer**: ✓ Monitor device motion using accelerometer and location speed. When speed drops below 0.5 m/s for 3+ seconds, auto-pause the timer and GPS. Display "Paused" UI. When speed increases above 1 m/s, auto-resume. Allow manual pause override. This prevents inflated workout times and provides accurate pace calculations. ### Question 5: Reflection **Question**: How can workout logging apps encourage healthy exercise habits without promoting overtraining or exercise addiction? **Answer**: ✓ Balance motivation with rest: include rest day recommendations, warn about excessive consecutive workouts, celebrate recovery (sleep quality, heart rate variability), avoid solely outcome-based rewards (focus on consistency over performance), provide educational content about overtraining signs, and never use fear-based motivation or negative comparisons. --- ## Lesson 12: Freemium Model Design ### Question 1: Vocabulary **Question**: What is a freemium model and how does it differ from a free trial? **Answer**: ✓ Freemium offers a permanently free version with limited features, where users can optionally upgrade to premium for more functionality. A free trial provides full access temporarily (e.g., 7 days) after which payment is required to continue. Freemium focuses on conversion through value demonstration; trials create urgency. ### Question 2: Code Understanding **Question**: What does this conditional rendering accomplish? ```javascript {isPremiumUser ? ( ) : ( )} ``` **Options**: - A) Shows analytics to all users - B) Shows analytics to premium users, upgrade prompt to free users ✓ - C) Hides analytics from all users - D) Shows a trial offer ### Question 3: Problem-Solving **Question**: Your freemium app has high downloads but low conversion to premium (only 1%). What strategies would you test to improve conversion? **Answer**: ✓ Test: (1) value-based feature gating (limit results, not access), (2) time-limited power user trials (let users experience premium briefly), (3) personalized upgrade prompts based on usage patterns, (4) social proof (show how many users upgraded), (5) pricing experiments (annual discount), and (6) upgrade surveys to understand why users don't convert. ### Question 4: Application **Question**: Design a freemium fitness app where free users get value but premium users get significantly more. **Answer**: ✓ Free: unlimited workout logging, basic stats (weekly totals), 3 pre-made workout plans, ads. Premium: advanced analytics (trends, predictions), custom workout builder, offline mode, nutrition tracking, no ads, coach chat support. Key: free tier must be genuinely useful (not a demo) but premium provides efficiency and depth. ### Question 5: Reflection **Question**: What ethical considerations arise when designing freemium conversion funnels? **Answer**: ✓ Avoid dark patterns: don't make free tier frustrating on purpose, don't hide costs or use manipulative urgency tactics ("Only 2 spots left!"), be transparent about limitations, don't gate essential safety features (e.g., emergency contacts in safety apps), respect user choice to stay free, and ensure ads (if used) don't compromise user experience or privacy. --- ## Lesson 13: Play Billing and IAP ### Question 1: Vocabulary **Question**: What is the difference between a consumable and non-consumable in-app purchase? **Answer**: ✓ Consumable IAPs are used up and can be purchased multiple times (e.g., coins, power-ups, extra storage), while non-consumable IAPs are permanent one-time purchases that persist across devices (e.g., ad removal, premium upgrade, content packs). ### Question 2: Code Understanding **Question**: What type of product is being purchased here? ```javascript const products = await IAP.getProducts(['remove_ads', 'premium_unlock']); const purchase = await IAP.requestPurchase('remove_ads'); if (purchase.productId === 'remove_ads') { await AsyncStorage.setItem('ads_removed', 'true'); await IAP.finishTransaction(purchase); } ``` **Options**: - A) A subscription - B) A consumable purchase - C) A non-consumable one-time purchase ✓ - D) A free product ### Question 3: Problem-Solving **Question**: A user claims they purchased "premium" but the app still shows ads. How would you debug and resolve this? **Answer**: ✓ Check: (1) verify purchase receipt with `getAvailablePurchases()` and validate on backend, (2) ensure `finishTransaction()` was called to acknowledge purchase, (3) check AsyncStorage/database for premium flag, (4) test restore purchases flow, (5) check for multiple Google accounts on device. Provide a "Restore Purchases" button prominently in settings. ### Question 4: Application **Question**: Implement a "tip jar" feature where users can optionally support your free app by purchasing $1, $5, or $10 tips. **Answer**: ✓ Create three consumable products (`tip_1`, `tip_5`, `tip_10`), display them as buttons with friendly labels ("Buy me a coffee ☕ $1"), on purchase success show thank you message with confetti animation, optionally unlock a "supporter" badge next to their username, and ensure `finishTransaction()` is called immediately (no persistent unlock needed). ### Question 5: Reflection **Question**: Why does Google/Apple take a 15-30% commission on IAP, and what value does this provide to developers? **Answer**: ✓ The commission covers: payment processing infrastructure (supports 100+ countries/currencies), fraud prevention and chargebacks, hosting purchase history, family sharing features, tax collection/remittance in various jurisdictions, customer support for payment issues, and maintaining the secure app distribution platform. Developers get global reach without building payment systems. --- ## Lesson 14: Subscriptions ### Question 1: Vocabulary **Question**: What is the difference between auto-renewable and non-renewing subscriptions? **Answer**: ✓ Auto-renewable subscriptions automatically charge users each billing period (monthly/yearly) until cancelled, providing continuous access. Non-renewing subscriptions are one-time purchases for a fixed duration (e.g., a season pass) that require manual re-purchase when they expire. ### Question 2: Code Understanding **Question**: What will this code check? ```javascript const subscriptions = await IAP.getAvailablePurchases(); const isActive = subscriptions.some(sub => sub.productId === 'monthly_premium' && new Date(sub.expiryDate) > new Date() ); ``` **Options**: - A) If the user has ever subscribed - B) If the user's monthly subscription is currently active ✓ - C) When the subscription was purchased - D) How much the subscription costs ### Question 3: Problem-Solving **Question**: Users complain about being charged after cancelling their subscription. What went wrong and how do you prevent this? **Answer**: ✓ Likely issue: subscription was cancelled but not before the renewal date. Educate users that cancellation prevents *future* renewals but doesn't refund the current period. Solutions: (1) clearly show "active until [date]" even after cancellation, (2) send reminder emails 3 days before renewal, (3) offer "cancel at end of period" vs "cancel immediately" options, (4) provide in-app subscription management link. ### Question 4: Application **Question**: Design a subscription tier system with monthly and annual options, where annual saves 20%. **Answer**: ✓ Products: `monthly_9.99` and `yearly_95.99`. Display side-by-side cards showing monthly at $9.99/month vs annual at $7.99/month (paid $95.99/year) with a "Save 20%" badge. Highlight annual as "Best Value." Allow switching between plans (pro-rate or at next renewal). Show total savings per year ($24) to encourage annual signup. ### Question 5: Reflection **Question**: What are the pros and cons of subscription-based monetization from a user perspective? **Answer**: ✓ Pros: lower upfront cost, continuous updates/improvements, try before commitment (free trials), family sharing, works across devices. Cons: subscription fatigue (too many monthly charges), total cost exceeds one-time purchase over time, risk of price increases, loss of access when stopping payment, and psychological burden of recurring commitments. --- ## Lesson 15: AdMob Integration ### Question 1: Vocabulary **Question**: What is the difference between banner ads, interstitial ads, and rewarded ads? **Answer**: ✓ Banner ads are small rectangular ads displayed persistently at top/bottom of screens. Interstitial ads are full-screen ads shown between content (e.g., level transitions). Rewarded ads give users in-app benefits (coins, lives) for watching a video ad to completion—these are opt-in and least disruptive. ### Question 2: Code Understanding **Question**: When will this ad be displayed? ```javascript interstitial.addAdEventListener('loaded', () => { interstitial.show(); }); interstitial.load(); ``` **Options**: - A) Immediately when the code runs - B) After the ad finishes loading from the network ✓ - C) When the user taps a button - D) Never (missing show() call) ### Question 3: Problem-Solving **Question**: Your rewarded ad video implementation sometimes doesn't grant the reward. How would you make it more reliable? **Answer**: ✓ Use proper event listeners: only grant reward on `'rewarded'` event (user watched full video), not on `'loaded'` or `'opened'`. Handle edge cases: save reward locally first, then sync to backend to prevent loss if app crashes. Check `rewarded` event payload for reward amount. Test on slow networks to ensure timeout handling. ### Question 4: Application **Question**: Implement a "remove ads for 24 hours" feature using rewarded ads instead of requiring payment. **Answer**: ✓ When user watches rewarded ad, store timestamp in AsyncStorage (`ad_free_until: Date.now() + 24*60*60*1000`). Before showing any ad, check if current time is before `ad_free_until`. Display countdown timer in UI showing hours remaining. Offer this as alternative to permanent "remove ads" IAP. This provides value to users who can't/won't pay. ### Question 5: Reflection **Question**: How can developers balance ad revenue with user experience to prevent app abandonment? **Answer**: ✓ Best practices: never show ads during critical tasks (checkout, emergencies), respect user focus time (no interstitials mid-article), limit frequency (max 1 interstitial per 5 minutes), make rewarded ads genuinely optional, avoid autoplay video with sound, provide "remove ads" IAP option, and never use deceptive ad placement (fake close buttons). Poor ad UX loses more revenue through churn than it gains. --- ## Lesson 16: Viral App Patterns ### Question 1: Vocabulary **Question**: What is a "viral coefficient" in app growth metrics? **Answer**: ✓ Viral coefficient (K) measures how many new users each existing user brings on average. K > 1 means exponential growth (each user brings more than one friend). K < 1 requires paid acquisition. Formula: K = (invites sent per user) × (conversion rate). Example: if users invite 5 friends and 40% join, K = 5 × 0.4 = 2.0. ### Question 2: Code Understanding **Question**: What sharing mechanism does this implement? ```javascript import * as Sharing from 'expo-sharing'; const shareAchievement = async () => { const uri = await captureScreen(); await Sharing.shareAsync(uri, { dialogTitle: 'I just hit 10,000 steps! 🎉' }); }; ``` **Options**: - A) Shares text only - B) Shares a screenshot of the achievement with custom message ✓ - C) Posts directly to social media - D) Sends an SMS invitation ### Question 3: Problem-Solving **Question**: Your referral program offers rewards but few users share invites. What psychological triggers could increase sharing? **Answer**: ✓ Triggers: (1) social proof ("500,000 users joined this week!"), (2) reciprocity (give both referrer and friend rewards), (3) scarcity ("limited beta access"), (4) status ("unlock VIP badge after 5 referrals"), (5) timing (prompt sharing right after positive experiences like achievements), and (6) reduce friction (pre-filled share messages, one-tap sharing). ### Question 4: Application **Question**: Design a feature where users can challenge friends to a 7-day step competition. **Answer**: ✓ Flow: user initiates challenge → selects friends from contacts or share link → friends accept via deep link → both track steps for 7 days → daily leaderboard updates → winner gets badge and bragging rights. Include push notifications for daily standings, trash talk messages, and easy re-challenge button. Make shareable results card showing winner's stats. ### Question 5: Reflection **Question**: What's the difference between organic virality and incentivized sharing, and which is more sustainable? **Answer**: ✓ Organic virality: users share because the experience is genuinely delightful/useful (e.g., sharing AR room photos). Incentivized: users share for rewards (coins, premium features). Organic is more sustainable because it indicates true product-market fit and doesn't depend on giving away value. Incentivized can jumpstart growth but may attract low-quality users who don't engage beyond claiming rewards. --- ## Lesson 17: Production and Launch ### Question 1: Vocabulary **Question**: What is the purpose of EAS (Expo Application Services) in deploying React Native apps? **Answer**: ✓ EAS is Expo's cloud service for building, submitting, and updating React Native apps. It provides managed build pipelines (iOS/Android), OTA (over-the-air) updates without app store approval, and automated submission to Google Play/App Store, simplifying the complex native build process for developers. ### Question 2: Code Understanding **Question**: What environment is this build configuration targeting? ```json { "build": { "production": { "android": { "buildType": "apk", "distribution": "store" } } } } ``` **Options**: - A) Development build for testing - B) Internal testing build - C) Production APK ready for Google Play Store submission ✓ - D) iOS App Store build ### Question 3: Problem-Solving **Question**: Your app is rejected from Google Play for "violating user data policy." What are common causes and how do you fix them? **Answer**: ✓ Common violations: (1) insufficient privacy policy (add detailed policy URL), (2) requesting permissions without clear justification (add permission modals explaining why), (3) accessing sensitive data unnecessarily (remove unused permissions from app.json), (4) data deletion capability missing (add account deletion feature), (5) not disclosing third-party SDKs (update data safety form). Review Play Console feedback and resubmit with corrections. ### Question 4: Application **Question**: Create a pre-launch checklist for submitting an AR furniture app to the Google Play Store. **Answer**: ✓ Checklist: - [ ] App bundle built with `eas build --platform android --profile production` - [ ] Privacy policy URL added (covering camera, location, user data) - [ ] ARCore requirement added to Play Console (filters non-compatible devices) - [ ] Store listing: 8 screenshots (include AR demo), feature graphic, short/full description - [ ] Content rating questionnaire completed - [ ] Data safety form filled (camera, storage permissions explained) - [ ] Internal testing with 10+ testers completed - [ ] All critical bugs fixed, crash rate < 1% - [ ] App signed with upload key and uploaded via Play Console ### Question 5: Reflection **Question**: Why is it important to test your app on a variety of real devices before launch? **Answer**: ✓ Reasons: emulators don't perfectly replicate real hardware (GPU performance, sensors, RAM constraints), device fragmentation means different Android versions/skins behave differently, screen size/resolution variations affect UI, real network conditions reveal loading issues, and sensor accuracy (GPS, ARCore, pedometer) varies by device. Physical testing catches edge cases that cause 1-star reviews and refunds. --- ## Completion Summary You've completed all 17 Exit Ticket assessments for M2: Mobile Platforms! ### Skills Assessed ✓ **Location Services**: Maps SDK, Places API, Directions, Geofencing ✓ **Augmented Reality**: ARCore fundamentals, 3D placement, interaction patterns ✓ **Health Integration**: Health Connect, step tracking, workout logging ✓ **Monetization**: Freemium models, IAP, subscriptions, AdMob ✓ **Growth**: Viral app patterns, sharing mechanics ✓ **Production**: EAS builds, app store submission, deployment ### Next Steps 1. Review any questions you missed 2. Complete certification requirements (70% average needed) 3. Build your capstone project **ShareSpot** 4. Continue to M3: Mobile Intelligence (AI integration) **Ready to ship apps that people love to share? Your portfolio awaits!**

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