React Native Technology & Digital Applications 4 — Questions and Answers
Question 1: How does `useEffect` with an empty dependency array behave in a React Native component?
- It runs once after the component mounts and the cleanup function runs on unmount (Correct answer)
- It runs on every render of the component
- It runs only when the component unmounts
- It runs before the component renders for the first time
Correct answer: It runs once after the component mounts and the cleanup function runs on unmount
An empty dependency array [] tells React to run the effect only once after the initial render, equivalent to componentDidMount in class components.
Question 2: Which Expo module lets a React Native app access and save images to the device camera roll?
- expo-media-library (Correct answer)
- expo-camera-roll
- expo-image-picker only
- expo-file-system
Correct answer: expo-media-library
expo-media-library provides APIs to read from and save assets to the device's photo library on both iOS and Android.
Question 3: What is the purpose of the `react-native-reanimated` library in React Native apps?
- To run animations entirely on the UI thread, avoiding bridge serialization jank (Correct answer)
- To replace the Animated API with CSS-based animations
- To provide pre-built animation presets like lottie files
- To schedule animations using requestAnimationFrame on the JS thread
Correct answer: To run animations entirely on the UI thread, avoiding bridge serialization jank
Reanimated 2+ uses worklets that execute on the UI thread, producing smooth 60/120fps animations even when the JS thread is busy.
Question 4: In React Native, which approach correctly prevents a TextInput from being obscured by the soft keyboard on iOS?
- Wrap the screen in KeyboardAvoidingView with behavior='padding' (Correct answer)
- Set keyboardType='none' on the TextInput
- Use ScrollView with keyboardDismissMode='on-drag'
- Add paddingBottom to the root View equal to the keyboard height
Correct answer: Wrap the screen in KeyboardAvoidingView with behavior='padding'
On iOS, KeyboardAvoidingView with behavior='padding' adds bottom padding equal to the keyboard height, keeping inputs visible.
Question 5: What does the `Pressable` component offer that `TouchableOpacity` does not?
- Granular pressed-state styling, hit slop configuration, and ripple effects via the style callback (Correct answer)
- Built-in accessibility roles without extra props
- Cross-platform gesture recognition with velocity tracking
- Automatic debouncing of rapid taps
Correct answer: Granular pressed-state styling, hit slop configuration, and ripple effects via the style callback
Pressable accepts a style function with a pressed argument, enabling fine-grained control over appearance on press, along with configurable hit areas.
Question 6: Which command regenerates native iOS files after changing dependencies in a React Native project?
- npx pod-install (or pod install inside the ios/ directory) (Correct answer)
- react-native run-ios --reset-cache
- npx react-native upgrade
- xcodebuild clean
Correct answer: npx pod-install (or pod install inside the ios/ directory)
pod install (via npx pod-install or directly inside the ios folder) fetches and links CocoaPods dependencies whenever the Podfile changes.
Question 7: What is the difference between `ScrollView` and `FlatList` in React Native?
- ScrollView renders all children at once; FlatList renders items lazily as they scroll into view (Correct answer)
- FlatList renders all items upfront; ScrollView renders lazily
- ScrollView only works horizontally; FlatList only works vertically
- FlatList requires a fixed item height; ScrollView supports dynamic heights
Correct answer: ScrollView renders all children at once; FlatList renders items lazily as they scroll into view
ScrollView mounts all child elements immediately, while FlatList virtualizes the list and only renders items near the visible viewport.
React Native Technology & Digital Applications 4
How does `useEffect` with an empty dependency array behave in a React Native component?