Interview questions in Mobile Dev, page 7
Structuring an auth flow in React Navigation
Conditionally render an auth stack versus app stack from state, not navigate calls; store token; let state drive screens.
How would you use Energy Log to investigate battery drain?
Tests correlating Instruments energy metrics to app behavior. Strong answers profile with Energy Log, map CPU/Location/Network spikes to user flows or background work, and validate fixes with before/after logs. Red flag: blaming the OS without evidence.
Fetch user profiles concurrently and handle individual failures
Tests Future.wait concurrency and per-future error isolation. Answer: map IDs to fetchProfile, pass to Future.wait. For partial failures, attach catchError per future to return null, then filter. Red flag: try-catch around Future.wait or sequential awaits.
What is AndroidManifest.xml and what key elements does it declare?
This tests your grasp of the system-app contract. Good answers cover component registration, permissions, and build metadata like package name and target SDK. A red flag is omitting install-time system discovery.
Purpose and Key Elements of AndroidManifest.xml
Tests if you know the manifest is the app's contract with the Android OS. A good answer defines its role and lists key elements like activities, permissions, and the launcher intent. A red flag is calling it just a generic 'config file'.
Describe the purpose of the AndroidManifest.xml file
This tests if you view the manifest as a contract with the OS. Define its role, then list key elements like components (<activity>), permissions (<uses-permission>), and hardware features. A red flag is just listing tags without explaining their purpose.
Refetching data when a screen gains focus
Use useFocusEffect with a useCallback callback; refetch on focus; clean up to abort stale requests.
When should you use frame-based layout versus Auto Layout?
Frames suit static or high-frequency UI like particle systems; Auto Layout handles rotation, Dynamic Type, localization, and split screen.
Explain StreamController, write a broadcast stream example, and why close it?
This tests Dart stream lifecycle and memory safety. A strong answer uses StreamController.broadcast(), adds data and errors, closes it, and explains unclosed controllers leak memory.
What is the difference between project-level and module-level build.gradle?
Project level sets plugin repos and shared versions; module level sets dependencies, build types, and flavors.
Difference between project and module build.gradle files?
This tests your understanding of Gradle's project structure and build configuration scope. The project-level file configures global settings like repositories, while the module-level file configures specifics like dependencies and app ID.
Project-level vs. module-level build.gradle files
This tests your grasp of Gradle's project/module structure. A good answer defines the project-level file for global settings (repositories, plugins) and the module-level for specifics (SDK versions, dependencies). A red flag is confusing their roles.
Accessing navigation outside a screen component
Use the useNavigation hook inside any component under NavigationContainer; for navigating outside React, use a navigationRef.
What is @State in SwiftUI and how does it affect the view?
Tests declarative data flow ownership. A strong answer defines @State as private value-type storage owned by the view that triggers a body re-evaluation on mutation. Red flag: confusing it with external data sources like @ObservedObject or @Binding.
Explain StatelessWidget vs StatefulWidget and when to choose each
This tests immutable UI versus persistent state. StatelessWidget rebuilds when config changes; StatefulWidget owns State surviving rebuilds. Use StatelessWidget for static UI and StatefulWidget for interactive elements.
What is the res directory and how do you use orientation qualifiers?
Res/ holds non-code assets; create layout-port/ and layout-land/ with identical XML filenames for automatic framework selection.
What is the `res/` directory and how do you use resource qualifiers?
This tests your grasp of Android's resource system. Explain that res/ separates assets from code and that qualifiers (e.g., layout-land) let the OS pick the right layout. A red flag is checking orientation manually in code instead of using this system.
Explain the res/ directory and resource qualifiers for layouts
Tests your grasp of Android's core resource system. A good answer defines res/ for non-code assets, explains how qualifiers like layout-land match device state, and provides a concrete example.
Setting screen options statically versus dynamically
Options prop on Screen (can read route) versus navigation.setOptions inside the screen for state-driven changes.
UIViewController lifecycle states: network vs geometry updates
Tests UIViewController lifecycle states and separation of data vs layout. Strong answers list loadView to viewDidDisappear, start network in viewDidLoad or viewWillAppear, and geometry in viewDidLayoutSubviews. Red flag: network calls inside layout methods.
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