What happens when you open a mobile app?
When a mobile app is launched, the operating system creates a process for it and loads its UI. If network access is needed, the app may initiate HTTP or TCP connections. The app lifecycle (foreground, background, inactive) also begins.
What is the mobile app lifecycle?
Depends on platform:
- iOS:
Not running → Inactive → Active → Background → Suspended - Android:
onCreate → onStart → onResume → onPause → onStop → onDestroy
Lifecycle events help manage resources and user experience.
What is an APK or IPA file?
- APK: Android Package, a zip file containing code, assets, manifest, resources, certificates.
- IPA: iOS App Store Package, a zip of compiled code, assets,
Info.plist, and provisioning profile.
Why are mobile apps sandboxed?
To prevent one app from accessing another’s data or interfering with the system. Sandboxing improves security and stability.
How does mobile handle network calls?
Mobile apps use libraries (like Retrofit, Alamofire, URLSession) to send HTTP/HTTPS requests. On Android, calls run on a background thread. On iOS, URLSession supports async calls.
What happens if the phone loses connection during a request?
Timeout or error will be thrown depending on configuration. Retry logic or caching strategies are often used to handle this.
What is push notification? How does it work?
A push notification is a message sent from server to mobile device. Steps:
- App registers with OS notification service (FCM for Android, APNs for iOS)
- Server sends notification via that service
- OS displays the message to the user
Difference between foreground and background push?
Foreground: App is active. App handles the notification manually.
Background: OS handles it and may show the message directly.
How is local storage handled in mobile apps?
Options include:
- Key-value storage (SharedPreferences, UserDefaults)
- SQLite or Room (Android), CoreData (iOS)
- Files (for media or documents)
How does a mobile app store login session?
Usually stored in:
- Secure storage (Keychain or EncryptedSharedPreferences)
- Local database
- In-memory if short-lived
What is deep linking?
Deep linking is when a link (e.g., myapp://profile/123) opens a specific screen inside an app. Helps improve UX and marketing campaigns.
What are App Permissions?
They define what system resources the app can access (camera, contacts, location…). Users must approve most of them at runtime.
What is mobile responsive design?
Mobile responsive design adapts UI for various screen sizes and resolutions. Uses flexible layouts, media queries, and scalable units.
What is the difference between native, hybrid, and cross-platform apps?
- Native: Built for a specific OS (Swift for iOS, Kotlin for Android)
- Hybrid: Web content in a native wrapper (e.g., Cordova)
- Cross-platform: One codebase, compiled to native (e.g., Flutter, React Native)
What is a crash log? How to analyze it?
A crash log contains stack trace and reason for crash. Tools like Firebase Crashlytics or Xcode Organizer help analyze it.
How does app update work?
- Android: Via Google Play, updated APK is downloaded and installed.
- iOS: Via App Store, same as above with signed IPA.
Apps check for updates via store metadata or internal API version checks.
What is mobile testing?
- Unit tests: for logic
- UI tests: simulate user interaction
- Manual testing: for UX and edge cases
- Tools: Espresso (Android), XCTest (iOS), Appium (cross-platform)
What are ANRs and how to avoid them?
ANR = Application Not Responding (Android). Happens when main thread is blocked for too long. Avoid by doing heavy work on background threads.
What is battery optimization in mobile apps?
Use background limits, job schedulers, and efficient network/data usage to reduce battery consumption.
How mobile apps handle multi-language?
Use localized string resources (strings.xml, Localizable.strings) and OS locale detection.
What is App Transport Security (ATS)?
ATS enforces HTTPS connections in iOS apps by default to improve security.
What is ProGuard / R8?
Android tool for shrinking, obfuscating, and optimizing code to reduce app size and improve security.
How to debug mobile network traffic?
Use tools like Charles Proxy, Proxyman, or Android Studio Network Inspector. Configure app to trust local SSL cert if using HTTPS.