Picker and date picker in React Native - Build, Publish & Deploy

Build & Publish - Picker and date picker

Performance Impact

Using Picker and Date Picker components in React Native generally has a low impact on frame rate and memory when used properly. These components are native wrappers, so they render smoothly at 60fps on most devices. However, excessive re-renders or complex state updates tied to picker changes can cause frame drops. Date pickers may trigger native modal dialogs, which are optimized but can briefly pause UI interaction.

Battery usage is minimal unless pickers are used in continuous loops or with heavy animations.

Optimization Tips

• Use React.memo or React.useCallback to prevent unnecessary re-renders of picker components.
• Keep picker options lists short or paginate them to avoid long rendering times.
• Debounce or throttle state updates triggered by picker changes to reduce UI thread load.
• Use native date picker dialogs instead of custom implementations for better performance and user experience.
• Avoid nesting pickers inside heavy scroll views without virtualization.

App Bundle Size and Startup Time

Picker and date picker components in React Native rely on native platform APIs and do not add significant size to the JavaScript bundle. Using the built-in @react-native-picker/picker and @react-native-community/datetimepicker packages adds minimal overhead (a few hundred KB) to the app size.

Startup time impact is negligible unless you preload large data sets for picker options at launch. Lazy load picker data when possible.

iOS vs Android Differences

• Picker: iOS uses a spinning wheel style picker by default, while Android uses a dropdown menu style. Behavior and styling differ, so test UI on both platforms.
• Date Picker: iOS shows a native wheel or calendar modal, Android shows a calendar or spinner dialog depending on version. Android dialogs may block UI interaction briefly.
• On iOS, date pickers can be embedded inline or modal; Android mostly uses modal dialogs.
• Customization options vary; Android pickers allow fewer style changes than iOS.

Store Review Guidelines

• Apple App Store: Ensure date and picker controls follow Apple Human Interface Guidelines for accessibility and usability.
• Use native pickers to avoid rejection for poor user experience or custom controls that confuse users.
• Support Dynamic Type and VoiceOver for accessibility.
• Google Play Store: Follow Material Design guidelines for pickers and date pickers.
• Ensure controls are responsive and accessible, with proper labels and touch targets.
• Sign your app bundle properly and test on multiple Android versions.

Self Check

Your app takes 5 seconds to load a screen with a picker and date picker. What is likely wrong?

• Loading a very large list of picker options synchronously on screen load.
• Heavy state updates or re-renders triggered by picker value changes.
• Using custom picker implementations instead of native components causing slow rendering.
• Not lazy loading or paginating picker data.

Key Result

Using native Picker and Date Picker components in React Native ensures smooth 60fps UI and minimal memory use. Optimize by limiting option lists and avoiding unnecessary re-renders. Follow platform-specific UI and accessibility guidelines to pass app store reviews.

Practice

1. What is the main purpose of a Picker component in React Native?

easy

A. To input text data

B. To display images in a gallery

C. To play audio files

D. To let users select one option from a list

Solution

1. Step 1: Understand Picker usage

   A Picker is designed to show a list of options for the user to choose from.

2. Step 2: Compare with other components

   Other options like text input or image gallery serve different purposes, not selection from a list.

3. Final Answer:

   To let users select one option from a list -> Option D

4. Quick Check:

   Picker = select one option [OK]

Hint: Picker is for choosing one item from many [OK]

Common Mistakes:

• Confusing Picker with text input
• Thinking Picker plays media
• Assuming Picker shows images

2. Which of the following is the correct way to import the Picker component from @react-native-picker/picker?

easy

A. import { Picker } from 'react-native';

B. import Picker from '@react-native-picker/picker';

C. import { Picker } from '@react-native-picker/picker';

D. import Picker from 'react-native-picker';

Solution

1. Step 1: Check official import syntax

   The Picker is exported as a named export from '@react-native-picker/picker', so curly braces are needed.

2. Step 2: Eliminate incorrect imports

   Default import from the correct package or imports from wrong packages are incorrect.

3. Final Answer:

   import { Picker } from '@react-native-picker/picker'; -> Option C

4. Quick Check:

   Named import with braces [OK]

Hint: Use curly braces for named imports like Picker [OK]

Common Mistakes:

• Using default import instead of named import
• Importing from wrong package
• Missing curly braces around Picker

3. Given this code snippet, what will be displayed when the user selects "Banana" from the Picker?

const [fruit, setFruit] = useState('Apple');

<Picker selectedValue={fruit} onValueChange={setFruit}>
  <Picker.Item label="Apple" value="Apple" />
  <Picker.Item label="Banana" value="Banana" />
  <Picker.Item label="Cherry" value="Cherry" />
</Picker>

<Text>Selected fruit: {fruit}</Text>

medium

A. Selected fruit: Banana

B. Selected fruit: undefined

C. Selected fruit: Cherry

D. Selected fruit: Apple

Solution

1. Step 1: Understand state update on selection

   The onValueChange calls setFruit with the selected value, updating the fruit state.

2. Step 2: Check selected value after choosing Banana

   When Banana is selected, fruit becomes 'Banana', so the Text shows 'Selected fruit: Banana'.

3. Final Answer:

   Selected fruit: Banana -> Option A

4. Quick Check:

   State updates to selected value = Banana [OK]

Hint: Selected value updates state shown in Text [OK]

Common Mistakes:

• Assuming state does not update on selection
• Confusing label and value
• Expecting default value always

4. Identify the error in this DatePicker usage:

const [date, setDate] = useState(new Date());

<DatePicker
  value={date}
  onChange={(event, selectedDate) => setDate(selectedDate)}
/>

medium

A. The 'value' prop should be 'date' instead of 'value'

B. The DatePicker component requires 'mode' prop

C. The 'onChange' callback parameters are incorrect

D. The 'setDate' function should not be called inside 'onChange'

Solution

1. Step 1: Review DatePicker required props

   React Native DatePicker requires a 'mode' prop like 'date' or 'time' to work properly.

2. Step 2: Check other props correctness

   'value' and 'onChange' usage is correct; 'setDate' is correctly called to update state.

3. Final Answer:

   The DatePicker component requires 'mode' prop -> Option B

4. Quick Check:

   Missing required 'mode' prop [OK]

Hint: DatePicker needs 'mode' prop to work [OK]

Common Mistakes:

• Omitting 'mode' prop causes no date shown
• Confusing 'value' with 'selected' prop
• Ignoring event parameter in onChange

5. You want to create a form with a Picker for selecting a country and a DatePicker for selecting a birthdate. How do you ensure the UI updates correctly when the user changes either input?

hard

A. Use separate state variables for country and birthdate, update each on change

B. Use a single state object and never update it

C. Only update state when the form is submitted

D. Use refs instead of state to track selections

Solution

1. Step 1: Manage state for each input separately

   Use one state variable for country and another for birthdate to track changes independently.

2. Step 2: Update state on user interaction

   Update the corresponding state in onValueChange for Picker and onChange for DatePicker to reflect UI changes.

3. Final Answer:

   Use separate state variables for country and birthdate, update each on change -> Option A

4. Quick Check:

   Separate states updated on change [OK]

Hint: Track each input with its own state variable [OK]

Common Mistakes:

• Using one state object but not updating it
• Delaying state update until submit
• Using refs instead of state for UI updates