Camera access (expo-camera) in React Native - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the expo-camera library in React Native?

The expo-camera library allows React Native apps to access and use the device's camera for taking photos and recording videos.

beginner

How do you request permission to use the camera with expo-camera?

You use the Camera.requestCameraPermissionsAsync() method to ask the user for permission to access the camera.

beginner

What React hook is commonly used to manage camera permission state in a functional component?

The useState hook is used to store and update the camera permission status (granted or denied).

intermediate

Why should you check camera permissions before rendering the camera view?

Checking permissions first ensures the app only tries to show the camera if the user has allowed access, preventing errors and improving user experience.

beginner

How do you display the camera preview on screen using expo-camera?

You render the <Camera> component from expo-camera and set its style and type (front or back camera).

Which method requests camera permission in expo-camera?

A Camera.getPermissions()

B Permissions.askCamera()

C Camera.requestCameraPermissionsAsync()

D Camera.enable()

The correct method to request camera permission is Camera.requestCameraPermissionsAsync().

What React hook is best to track if camera permission is granted?

A useState

B useContext

C useRef

D useEffect

The useState hook is used to store and update permission status.

Which component shows the live camera feed in expo-camera?

A <Camera>

B <CameraFeed>

C <CameraView>

D <CameraPreview>

The <Camera> component displays the live camera preview.

What should you do if camera permission is denied?

A Force camera to open anyway

B Show an error message or alternative UI

C Restart the app

D Ignore and continue

If permission is denied, show a message or alternative UI to inform the user.

Which camera type can you select in expo-camera?

A Only front camera

B No camera selection possible

C Only back camera

D Front or back camera

You can choose between front and back cameras using the type prop.

Explain how to request and handle camera permissions using expo-camera in a React Native app.

Think about asking the user first, then showing the camera only if allowed.

Describe how to display a live camera preview using the expo-camera library.

Focus on the component and props needed for the preview.

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