Picker and date picker in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Picker component from @react-native-picker/picker.

React Native

import { [1] } from '@react-native-picker/picker';

Drag options to blanks, or click blank then click option'

ASelect

BDatePicker

CPicker

DDropdown

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'DatePicker' instead of 'Picker'.

Trying to import 'Select' which is not from this package.

The Picker component is imported from '@react-native-picker/picker' as Picker.

2fill in blank

medium

Complete the code to set the selected value state for the Picker component.

React Native

const [selectedValue, setSelectedValue] = useState([1]);

Drag options to blanks, or click blank then click option'

A"java"

Bnull

C0

D""

Attempts:

3 left

💡 Hint

Common Mistakes

Setting initial value to null or empty string which does not match any Picker item.

Using a number instead of a string.

The initial selected value is set to the string "java" to match one of the Picker items.

3fill in blank

hard

Fix the error in the Picker onValueChange handler to update the selected value.

React Native

<Picker
  selectedValue={selectedValue}
  onValueChange={(itemValue, itemIndex) => [1]
>

Drag options to blanks, or click blank then click option'

AsetSelectedValue(itemIndex)

BsetSelectedValue(itemValue)

CselectedValue = itemValue

DsetSelectedValue()

Attempts:

3 left

💡 Hint

Common Mistakes

Passing itemIndex instead of itemValue.

Trying to assign directly to selectedValue which is read-only.

The onValueChange handler should call setSelectedValue with the new itemValue to update the state.

4fill in blank

hard

Fill both blanks to create a DateTimePicker that shows when showPicker is true and updates the date state.

React Native

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

<DateTimePicker
  value={date}
  mode=[1]
  display="default"
  onChange={(event, selectedDate) => {
    setShowPicker(false);
    if (selectedDate) {
      [2];
    }
  }}
/>

Drag options to blanks, or click blank then click option'

A"date"

BsetDate(selectedDate)

CsetDate(event)

D"time"

Attempts:

3 left

💡 Hint

Common Mistakes

Using mode "time" instead of "date".

Calling setDate with the event object instead of selectedDate.

The mode should be set to "date" to pick a date, and the onChange handler should update the date state by calling setDate(selectedDate).

5fill in blank

hard

Fill all three blanks to show the Picker with three items and update the selected value on change.

React Native

const [selected, setSelected] = useState("apple");

<Picker
  [3]=[1]
  onValueChange={value => [2]
>
  <Picker.Item label="Apple" value="apple" />
  <Picker.Item label="Banana" value="banana" />
  <Picker.Item label="Cherry" value="cherry" />
</Picker>

Drag options to blanks, or click blank then click option'

Aselected

BsetSelected(value)

CsetSelectedValue(value)

DselectedValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong setter function name like setSelectedValue instead of setSelected.

Confusing the prop name with the state variable.

The Picker's selectedValue prop should be the state variable selected. The onValueChange handler should call setSelected(value) to update the state. The last blank is the prop name selectedValue used in the Picker component.

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