Pull-to-refresh in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the React hook needed for pull-to-refresh.

React Native

import React, { [1] } from 'react';

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

AuseCallback

BuseEffect

CuseState

DuseRef

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing useState or useEffect instead of useCallback.

The useCallback hook is used to memoize the refresh function for pull-to-refresh.

2fill in blank

medium

Complete the code to set the refreshing state variable.

React Native

const [refreshing, [1]] = React.useState(false);

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

AsetRefresh

BsetRefreshing

CrefreshSet

DrefreshingSet

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect setter names like setRefresh or refreshingSet.

The setter function for the refreshing state is conventionally named setRefreshing.

3fill in blank

hard

Fix the error in the refresh function to correctly update the refreshing state.

React Native

const onRefresh = React.useCallback(() => {
  [1](true);
  setTimeout(() => [1](false), 2000);
}, []);

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

ArefreshSet

Brefreshing

CsetRefresh

DsetRefreshing

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the state variable instead of the setter function.

The function setRefreshing must be called to update the refreshing state.

4fill in blank

hard

Fill both blanks to add pull-to-refresh to the FlatList component.

React Native

<FlatList
  data={data}
  renderItem={renderItem}
  keyExtractor={item => item.id}
  refreshing=[1]
  onRefresh=[2]
/>

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

Arefreshing

BonRefresh

ConRefresh()

Drefreshing()

Attempts:

3 left

💡 Hint

Common Mistakes

Using function calls instead of references for onRefresh.

Passing wrong prop names.

The refreshing prop takes the boolean state, and onRefresh takes the function to call on pull.

5fill in blank

hard

Fill all three blanks to complete the pull-to-refresh example with FlatList.

React Native

import React, { [1] } from 'react';
import { FlatList } from 'react-native';

export default function App() {
  const [refreshing, [2]] = React.useState(false);

  const onRefresh = React.useCallback(() => {
    [2](true);
    setTimeout(() => [2](false), 1500);
  }, []);

  return (
    <FlatList
      data={[{id: '1'}, {id: '2'}]}
      keyExtractor={item => item.id}
      renderItem={({item}) => <></>}
      refreshing={refreshing}
      onRefresh={onRefresh}
    />
  );
}

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

AuseCallback

BsetRefreshing

CuseState

DsetRefresh

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing useState and useCallback imports.

Using wrong setter function names.

We import useCallback, use useState to create refreshing and setRefreshing, and call setRefreshing to update state.

Practice

1. What is the main purpose of using RefreshControl in a React Native app?

easy

A. To enable pull-to-refresh functionality in scrollable lists

B. To add animations to buttons

C. To handle navigation between screens

D. To style text components

Solution

1. Step 1: Understand the role of RefreshControl

   RefreshControl is a component used inside scrollable views to provide pull-to-refresh behavior.

2. Step 2: Identify its main purpose

   Its main purpose is to let users pull down on a list to trigger a refresh action, usually to update content.

3. Final Answer:

   To enable pull-to-refresh functionality in scrollable lists -> Option A

4. Quick Check:

   Pull-to-refresh = RefreshControl usage [OK]

Hint: RefreshControl is for pull-to-refresh in lists [OK]

Common Mistakes:

• Confusing RefreshControl with navigation or styling
• Thinking it adds animations to buttons
• Using it outside scrollable components

2. Which of the following is the correct way to use RefreshControl inside a ScrollView?

easy

A.

B.

C. } />

D. } />

Solution

1. Step 1: Recall correct RefreshControl usage

   The refreshControl prop expects a RefreshControl component with props refreshing and onRefresh.

2. Step 2: Match correct syntax

   <ScrollView refreshControl={<RefreshControl refreshing={refreshing} onRefresh={onRefresh} />} /> correctly passes refreshing and onRefresh inside <RefreshControl /> as a JSX element.

3. Final Answer:

   <ScrollView refreshControl={<RefreshControl refreshing={refreshing} onRefresh={onRefresh} />} /> -> Option D

4. Quick Check:

   refreshControl prop = RefreshControl component with correct props [OK]

Hint: Use refreshControl prop with RefreshControl JSX [OK]

Common Mistakes:

• Passing props directly to ScrollView instead of RefreshControl
• Calling RefreshControl as a function instead of JSX
• Using wrong prop names like refresh or refreshHandler

3. Given this code snippet, what will happen when the user pulls down the list?

const [refreshing, setRefreshing] = React.useState(false);

const onRefresh = React.useCallback(() => {
  setRefreshing(true);
  setTimeout(() => setRefreshing(false), 2000);
}, []);

return (
  <ScrollView refreshControl={
    <RefreshControl refreshing={refreshing} onRefresh={onRefresh} />
  }>
    <Text>Pull down to refresh</Text>
  </ScrollView>
);

medium

A. The spinner never shows because refreshing is false

B. The spinner shows for 2 seconds, then hides automatically

C. The spinner shows indefinitely and never hides

D. The app crashes due to missing dependencies

Solution

1. Step 1: Understand the refreshing state changes

   When the user pulls down, onRefresh sets refreshing to true, showing the spinner.

2. Step 2: Analyze the timeout effect

   After 2 seconds, setRefreshing(false) hides the spinner automatically.

3. Final Answer:

   The spinner shows for 2 seconds, then hides automatically -> Option B

4. Quick Check:

   refreshing true then false after timeout = spinner shows then hides [OK]

Hint: Refreshing true shows spinner; false hides it [OK]

Common Mistakes:

• Assuming spinner never hides without manual reset
• Thinking refreshing starts as true initially
• Confusing useCallback dependencies causing crashes

4. Identify the error in this pull-to-refresh implementation:

const [refreshing, setRefreshing] = React.useState(false);

function onRefresh() {
  setRefreshing(true);
  fetchData();
  setRefreshing(false);
}

return (
  <FlatList
    data={data}
    refreshControl={<RefreshControl refreshing={refreshing} onRefresh={onRefresh} />}
    renderItem={({item}) => <Text>{item}</Text>}
  />
);

medium

A. onRefresh should be async but is not

B. refreshControl prop should be refreshControl (lowercase c)

C. setRefreshing(false) is called immediately, hiding spinner too soon

D. FlatList does not support RefreshControl

Solution

1. Step 1: Check refreshing state timing

   The function calls setRefreshing(false) immediately after fetchData(), without waiting for data to load.

2. Step 2: Understand spinner behavior

   This causes the spinner to hide right away, not showing the loading state properly.

3. Final Answer:

   setRefreshing(false) is called immediately, hiding spinner too soon -> Option C

4. Quick Check:

   Refreshing state must stay true until data loads [OK]

Hint: Keep refreshing true until data fetch completes [OK]

Common Mistakes:

• Calling setRefreshing(false) too early
• Misnaming refreshControl prop
• Assuming FlatList can't use RefreshControl

5. You want to add pull-to-refresh to a SectionList that fetches new data asynchronously. Which approach correctly ensures the spinner shows during fetch and hides after completion?

const [refreshing, setRefreshing] = React.useState(false);

const onRefresh = async () => {
  // What goes here?
};

hard

A. setRefreshing(true); await fetchData(); setRefreshing(false);

B. await fetchData(); setRefreshing(true); setRefreshing(false);

C. setRefreshing(false); await fetchData(); setRefreshing(true);

D. setRefreshing(true); fetchData(); setRefreshing(false);

Solution

1. Step 1: Set refreshing true before fetching

   Call setRefreshing(true) to show spinner before starting data fetch.

2. Step 2: Await fetchData and then set refreshing false

   Use await fetchData() to wait for data, then call setRefreshing(false) to hide spinner after completion.

3. Final Answer:

   setRefreshing(true); await fetchData(); setRefreshing(false); -> Option A

4. Quick Check:

   Show spinner before await, hide after await [OK]

Hint: Set refreshing true before await, false after await [OK]

Common Mistakes:

• Setting refreshing false before fetch completes
• Not awaiting fetchData causing spinner to hide early
• Switching order of setRefreshing calls