Intermediate everything in Mobile Dev, page 14
Unit test a BLoC handling an AddItem event and emitting state
Use blocTest with build, act, expect; mention seed, skip, and mocktail for dependencies.
How do you widget-test states without real network calls?
This tests UI isolation from I/O. Mock the repository with Mockito, stub methods to yield loading, success, and error, and inject it via constructor or provider. Avoid real HTTP calls or unmocked clients in widget tests.
Safely gating native OS version APIs in a custom Flutter plugin
Tests platform channel contracts and defensive native coding. Gate native calls with OS version checks, return result.error with an UNSUPPORTED code, handle PlatformException in Dart, and avoid Dart-only checks.
What is a Platform View and why is it crucial?
Tests embedding native UI when Flutter widgets fall short. Strong answers define Platform Views as native embeddings, cite maps or WebView, and contrast Hybrid Composition's native hierarchy with Virtual Display's texture rasterization.
When to choose EventChannel over MethodChannel and native setup
It tests streaming versus one-shot platform communication. Pick EventChannel for ongoing native events like sensor data; register a StreamHandler on Android or iOS that feeds an event sink, then consume in Dart via receiveBroadcastStream.
How would you draw a line graph using Canvas and Path?
Use moveTo for the first point, lineTo for the rest, then Canvas.drawPath with a stroke Paint.
In a CustomPainter, what is the purpose of the shouldRepaint method?
This tests Flutter repaint optimization. Answer: shouldRepaint compares old and new delegates, returning true only when visual properties differ so the framework skips paint calls. A red flag is returning true unconditionally, forcing useless repaints.
How does Tween work and how do you use ColorTween with Curves?
This tests value interpolation versus time remapping. A strong answer: Tween maps 0-1 to typed values; ColorTween lerps 2 colors; Curves.easeInOut warps input time before interpolation. Red flag: claiming the curve alters the color output instead of timing.
Compare AnimatedBuilder and Transition widgets for explicit animations
Tests whether you know how explicit animations rebuild the widget tree and where to isolate animation effects. AnimatedBuilder rebuilds only its builder subtree, while Transition widgets rebuild their child when the animation ticks.
What is an sqflite transaction? Provide a practical example.
Tests atomicity in SQLite and isolate safety. A strong answer defines all-or-nothing execution, gives a fund-transfer example updating both, and warns sqflite transactions are not cross-isolate safe. Red flag: omitting rollback or multi-isolate writes.
Key difference between shared_preferences and flutter_secure_storage for tokens
Tests at-rest encryption: shared_preferences stores plain text XML/plist, while secure storage uses iOS Keychain and Keystore with RSA OAEP plus AES-GCM. Answers cite backup risks and hardware keys. Red flag: calling prefs safe or relying on obfuscation.
Why is Flutter local storage async and how do you use shared_preferences?
Tests why disk I/O must avoid blocking Dart's UI thread. A strong answer shows async/await with getInstance and setters, notes legacy getters are sync-after-cache, and warns writes may not persist instantly.
How would you manage network request state in a Flutter widget?
This tests whether you separate ephemeral widget state from business logic. A good answer defines a state class, uses setState in initState, then shows how a library moves logic out for testing and reuse. Red flag: fetch inside build or using boolean flags.
Compare manual JSON serialization versus json_serializable
It tests build automation versus manual control in Dart serialization. Manual methods avoid build steps but risk drift; code generation cuts boilerplate but adds compile latency. Claiming code gen slows runtime or that manual is always simpler.
Describe a robust error handling strategy for network requests
Tests whether you classify failures by layer rather than catching everything generically. Inspect DioExceptionType for connectivity, check HTTP status before parsing, and isolate JSON decode errors. Never show the same message for timeouts and 500s.
Explain lifting state up in Flutter and how Provider simplifies it
Tests declarative state ownership and prop-drilling cost. A strong answer names the lowest common ancestor, contrasts callback threading with Provider lookup, and avoids root-level state.
How do you manage product list and favorite state without full rebuilds?
This tests granular rebuild control in Flutter lists. A strong answer isolates item state with ValueNotifier or ChangeNotifier per item plus const constructors with keys. Red flag: calling setState on the parent list rebuilds every ListTile on each tap.
Difference between context.watch, context.read, and Selector in Provider and Riverpod
Tests rebuild granularity in Flutter. A strong answer distinguishes listening versus one-time lookup, explains that Selector filters rebuilds by comparing sub-values, and warns that context.read inside build causes missed updates.
Implement a GoRouter path parameter route and access userId in a widget
This tests GoRouter declarative routing and GoRouterState. Define a GoRoute with path '/users/:userId', read state.params['userId'] in the builder, and handle null-safety. A red flag is parsing the URI manually or using ModalRoute.of instead of state.params.
Explain the core responsibilities of RouterDelegate, RouteInformationParser, and Router in Flutter
Tests Navigator 2.0 architecture split. RouteInformationParser converts URLs to typed config; RouterDelegate owns state and builds the Navigator; Router wires them together and handles engine intents. Red flag: conflating parsing and state or omitting Router.
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