Camera access (expo-camera) in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the CameraView component from expo-camera.

React Native

import { [1] } from 'expo-camera';

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

ACamera

BCameraAccess

CCameraModule

DCameraView

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect component names like CameraView or CameraModule.

Forgetting to import from 'expo-camera'.

The correct import is Camera from expo-camera. This component allows you to access the device camera.

2fill in blank

medium

Complete the code to request camera permissions using the hook.

React Native

const [permission, requestPermission] = [1]();

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

AuseCamera

BuseCameraPermissions

CuseCameraAccess

DuseCameraRequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using hooks that do not exist like useCamera or useCameraRequest.

Confusing permission request with camera usage.

The hook useCameraPermissions is used to get and request camera permissions in expo-camera.

3fill in blank

hard

Fix the error in the code to check if permission is granted before rendering the camera component.

React Native

if (!permission?.[1]) {
  return <Text>No access to camera</Text>;
}

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

Aaccepted

Ballowed

Cgranted

Denabled

Attempts:

3 left

💡 Hint

Common Mistakes

Using properties like allowed or enabled which do not exist.

Checking permission without optional chaining causing errors.

The permission object has a granted property that is true when the user has allowed camera access.

4fill in blank

hard

Fill both blanks to render the CameraView component with the back camera facing and a style.

React Native

<CameraView facing=[1] style=[2] />

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

A"back"

B"front"

C{ flex: 1 }

D{ width: 100 }

Attempts:

3 left

💡 Hint

Common Mistakes

Using front camera instead of back.

Using incorrect style objects that do not fill space.

The back camera is selected with "back". The style { flex: 1 } makes the camera fill the available space.

5fill in blank

hard

Fill all three blanks to request permission on button press and handle the response.

React Native

async function askPermission() {
  const { status } = await [1]();
  if (status === [2]) {
    [3](true);
  } else {
    [3](false);
  }
}

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

ArequestPermission

B"granted"

CsetHasPermission

DgetCameraPermissionsAsync

Attempts:

3 left

💡 Hint

Common Mistakes

Using getCameraPermissionsAsync instead of requestPermission.

Comparing status to incorrect strings.

Not calling the correct state setter.

The function requestPermission asks the user for camera access. The status is compared to the string "granted". The state setter setHasPermission updates the permission state.

Practice

1. What is the first step to use the camera in a React Native app with expo-camera?

easy

A. Directly show the camera preview

B. Request permission to access the camera

C. Take a picture immediately

D. Install a photo editing library

Solution

1. Step 1: Understand permission requirement

   Mobile apps must ask user permission before accessing hardware like the camera.

2. Step 2: Request camera permission first

   Using expo-camera, you call permission request functions before showing the camera.

3. Final Answer:

   Request permission to access the camera -> Option B

4. Quick Check:

   Permission request = A [OK]

Hint: Always ask permission before using hardware [OK]

Common Mistakes:

• Trying to show camera preview without permission
• Taking picture before permission granted
• Skipping permission request step

2. Which of the following is the correct way to import the Camera component from expo-camera?

easy

A. import Camera from 'expo-camera';

B. import CameraComponent from 'expo-camera';

C. import * as Camera from 'expo-camera';

D. import { Camera } from 'expo-camera';

Solution

1. Step 1: Check expo-camera export style

   The Camera component is a named export, so it must be imported with curly braces.

2. Step 2: Use correct import syntax

   Correct syntax is import { Camera } from 'expo-camera'; to access the Camera component.

3. Final Answer:

   import { Camera } from 'expo-camera'; -> Option D

4. Quick Check:

   Named import uses curly braces = D [OK]

Hint: Named exports need curly braces in import [OK]

Common Mistakes:

• Using default import without braces
• Importing everything as an object
• Using wrong import names

3. What will be the output of this code snippet inside a React Native component using expo-camera?

const [hasPermission, setHasPermission] = React.useState(null);
React.useEffect(() => {
  (async () => {
    const { status } = await Camera.requestCameraPermissionsAsync();
    setHasPermission(status === 'granted');
  })();
}, []);

return hasPermission === null ? Requesting permission : hasPermission === false ? No access : ;

medium

A. Shows camera preview immediately without permission

B. Shows 'No access' text always

C. Shows 'Requesting permission' text initially, then camera preview if granted

D. Throws a syntax error

Solution

1. Step 1: Analyze permission state flow

   Initially, hasPermission is null, so it shows 'Requesting permission'.

2. Step 2: After permission request

   If permission granted, hasPermission becomes true and camera preview shows; if denied, shows 'No access'.

3. Final Answer:

   Shows 'Requesting permission' text initially, then camera preview if granted -> Option C

4. Quick Check:

   Permission null -> text, granted -> camera = B [OK]

Hint: Check initial state null shows loading text [OK]

Common Mistakes:

• Expecting camera preview before permission granted
• Confusing permission states
• Ignoring async permission request

4. Identify the error in this React Native code snippet using expo-camera:

const cameraRef = React.useRef(null);

async function takePicture() {
  if (cameraRef) {
    const photo = await cameraRef.current.takePictureAsync();
    console.log(photo.uri);
  }
}

medium

A. cameraRef should be checked as cameraRef.current, not cameraRef

B. takePictureAsync() is not an async function

C. cameraRef must be a state variable, not a ref

D. console.log cannot print photo.uri

Solution

1. Step 1: Check cameraRef usage

   cameraRef is a ref object; to access the camera instance, use cameraRef.current.

2. Step 2: Correct condition check

   The condition should check if (cameraRef.current) to ensure the camera is ready.

3. Final Answer:

   cameraRef should be checked as cameraRef.current, not cameraRef -> Option A

4. Quick Check:

   Ref object needs .current to access value = C [OK]

Hint: Check .current on refs before use [OK]

Common Mistakes:

• Checking ref object directly instead of .current
• Forgetting async on takePictureAsync
• Misusing console.log for URIs

5. You want to build a React Native app that takes a photo only if the user grants camera permission and then saves the photo URI in state. Which sequence of steps is correct?

hard

A. Request permission -> Show camera preview -> Use ref to take picture -> Save URI in state

B. Show camera preview -> Take picture -> Request permission -> Save URI in state

C. Take picture -> Request permission -> Show camera preview -> Save URI in state

D. Save URI in state -> Request permission -> Show camera preview -> Take picture

Solution

1. Step 1: Request permission before camera use

   Always ask and confirm permission before showing camera preview.

2. Step 2: Show camera preview and take picture

   Use a ref to access the camera and take a picture only after permission granted.

3. Step 3: Save photo URI in state

   Store the photo URI in state to use or display later in the app.

4. Final Answer:

   Request permission -> Show camera preview -> Use ref to take picture -> Save URI in state -> Option A

5. Quick Check:

   Permission first, then camera, then save = A [OK]

Hint: Permission first, then camera, then save URI [OK]

Common Mistakes:

• Taking picture before permission
• Saving URI before picture taken
• Showing camera without permission