Camera access in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Camera Preview Display

What will be the visible result when this Kotlin Android code runs in an app with camera permission granted?

Android Kotlin

class CameraPreviewActivity : AppCompatActivity() {
  private lateinit var cameraProviderFuture: ListenableFuture<ProcessCameraProvider>

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    val previewView = PreviewView(this)
    setContentView(previewView)

    cameraProviderFuture = ProcessCameraProvider.getInstance(this)
    cameraProviderFuture.addListener({
      val cameraProvider = cameraProviderFuture.get()
      val preview = Preview.Builder().build().also {
        it.setSurfaceProvider(previewView.surfaceProvider)
      }
      val cameraSelector = CameraSelector.DEFAULT_BACK_CAMERA
      cameraProvider.bindToLifecycle(this, cameraSelector, preview)
    }, ContextCompat.getMainExecutor(this))
  }
}

A The app shows a live camera preview from the back camera filling the screen.

B The app shows a blank white screen with no camera preview.

C The app crashes with a NullPointerException because previewView is not initialized.

D The app shows a static image instead of a live camera preview.

💡 Hint

Think about what PreviewView and bindToLifecycle do in CameraX.

The code sets up a PreviewView and binds the back camera preview to it using CameraX. This shows a live camera feed filling the screen.

❓ lifecycle

intermediate

Camera Lifecycle Binding

What happens if you bind the camera to a lifecycle owner that is already destroyed?

A The camera preview stops immediately and no image is shown.

B The camera preview continues to run in the background.

C The app throws an IllegalStateException at runtime.

D The app silently ignores the binding and shows a blank screen.

💡 Hint

Consider how CameraX manages lifecycle states.

Binding to a destroyed lifecycle owner causes CameraX to throw an IllegalStateException because it cannot manage camera resources properly.

📝 Syntax

advanced

Correct Permission Request Code

Which Kotlin code snippet correctly requests camera permission at runtime in an Android app?

Android Kotlin

val CAMERA_PERMISSION = android.Manifest.permission.CAMERA

fun requestCameraPermission(activity: Activity) {
  if (ContextCompat.checkSelfPermission(activity, CAMERA_PERMISSION) != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(activity, arrayOf(CAMERA_PERMISSION), 100)
  }
}

A

if (ContextCompat.checkSelfPermission(activity, CAMERA_PERMISSION) != PackageManager.PERMISSION_GRANTED) {
  ActivityCompat.requestPermissions(activity, arrayOf(CAMERA_PERMISSION), 100)
}

B

if (ContextCompat.checkSelfPermission(activity, CAMERA_PERMISSION) == PackageManager.PERMISSION_GRANTED) {
  ActivityCompat.requestPermissions(activity, arrayOf(CAMERA_PERMISSION), 100)
}

C ActivityCompat.requestPermissions(activity, arrayOf(CAMERA_PERMISSION), 100)

D

if (ActivityCompat.checkSelfPermission(activity, CAMERA_PERMISSION) != PackageManager.PERMISSION_GRANTED) {
  ActivityCompat.requestPermissions(activity, arrayOf(CAMERA_PERMISSION), 100)
}

💡 Hint

Check the condition for when to request permission.

You request permission only if it is NOT already granted. Option A correctly checks for not granted and then requests permission.

🔧 Debug

advanced

Camera Preview Not Showing

Why does this code fail to show the camera preview even though permissions are granted?

Android Kotlin

class MainActivity : AppCompatActivity() {
  private lateinit var previewView: PreviewView

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    previewView = PreviewView(this)
    setContentView(previewView)

    val cameraProviderFuture = ProcessCameraProvider.getInstance(this)
    cameraProviderFuture.addListener({
      val cameraProvider = cameraProviderFuture.get()
      val preview = Preview.Builder().build()
      val cameraSelector = CameraSelector.DEFAULT_BACK_CAMERA
      preview.setSurfaceProvider(previewView.surfaceProvider)
      cameraProvider.bindToLifecycle(this, cameraSelector, preview)
    }, ContextCompat.getMainExecutor(this))
  }
}

A cameraProviderFuture.get() is called on the main thread causing a deadlock.

B previewView is not added to the layout, so preview cannot display.

C Camera permission is missing in the manifest, so preview fails silently.

D preview.setSurfaceProvider is called after bindToLifecycle, so preview has no surface when bound.

💡 Hint

Check the order of setting the surface provider and binding the preview.

The surface provider must be set before binding the preview to lifecycle. Calling setSurfaceProvider after bindToLifecycle means the preview has no surface to display on when bound.

🧠 Conceptual

expert

CameraX Use Cases

Which CameraX use case should you use to capture a high-quality still photo with automatic focus and flash support?

A Preview use case, because it shows live camera feed and can capture photos.

B ImageCapture use case, because it supports high-quality photo capture with focus and flash.

C ImageAnalysis use case, because it processes images and saves photos automatically.

D VideoCapture use case, because it can capture both photos and videos with focus.

💡 Hint

Think about which use case is designed for still photo capture.

ImageCapture use case is designed for taking high-quality photos with features like autofocus and flash. Preview only shows live feed, ImageAnalysis is for processing frames, VideoCapture is for videos.

Practice

1. What is the main purpose of using MediaStore.ACTION_IMAGE_CAPTURE in an Android app?

easy

A. To open the device camera to take a photo

B. To open the device gallery to select a photo

C. To record audio using the microphone

D. To access device location services

Solution

1. Step 1: Understand the intent action

   MediaStore.ACTION_IMAGE_CAPTURE is a predefined intent action to launch the camera app for capturing images.

2. Step 2: Identify the purpose in the app

   This intent opens the camera so the user can take a photo, which the app can then receive.

3. Final Answer:

   To open the device camera to take a photo -> Option A

4. Quick Check:

   Camera intent = open camera [OK]

Hint: Remember: ACTION_IMAGE_CAPTURE means open camera [OK]

Common Mistakes:

• Confusing camera intent with gallery intent
• Thinking it records audio
• Assuming it accesses location

2. Which of the following is the correct Kotlin syntax to start the camera intent for result in an Activity?

easy

A. startActivityForResult(Intent(MediaStore.ACTION_IMAGE_CAPTURE), REQUEST_CODE)

B. startActivity(Intent(MediaStore.ACTION_IMAGE_CAPTURE))

C. startActivityForResult(MediaStore.ACTION_IMAGE_CAPTURE, REQUEST_CODE)

D. startActivityForResult(Intent(REQUEST_CODE), MediaStore.ACTION_IMAGE_CAPTURE)

Solution

1. Step 1: Check the method signature

   startActivityForResult requires an Intent and a request code integer.

2. Step 2: Verify the Intent creation

   The Intent must be created with MediaStore.ACTION_IMAGE_CAPTURE as the action.

3. Final Answer:

   startActivityForResult(Intent(MediaStore.ACTION_IMAGE_CAPTURE), REQUEST_CODE) -> Option A

4. Quick Check:

   Intent + request code = startActivityForResult [OK]

Hint: Intent first, then request code in startActivityForResult [OK]

Common Mistakes:

• Passing action string instead of Intent
• Omitting request code
• Swapping Intent and request code parameters

3. Given this code snippet in an Activity, what will be the output when the user takes a photo successfully?

override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
  super.onActivityResult(requestCode, resultCode, data)
  if (requestCode == REQUEST_CODE && resultCode == RESULT_OK) {
    val photo = data?.extras?.get("data") as Bitmap
    imageView.setImageBitmap(photo)
  }
}

medium

A. The app will display a default image instead

B. The app will crash due to a null pointer exception

C. Nothing happens because onActivityResult is not called

D. The photo taken by the user will be displayed in imageView

Solution

1. Step 1: Understand onActivityResult behavior

   This method receives the result from the camera intent when the user takes a photo.

2. Step 2: Check the code logic

   If the request and result codes match, it extracts the photo bitmap from the intent extras and sets it to the imageView.

3. Final Answer:

   The photo taken by the user will be displayed in imageView -> Option D

4. Quick Check:

   Photo bitmap set to imageView = display photo [OK]

Hint: Check requestCode and resultCode before using data [OK]

Common Mistakes:

• Not checking requestCode or resultCode
• Casting data extras incorrectly
• Forgetting to call super.onActivityResult

4. Identify the error in this Kotlin code snippet for launching the camera:

val intent = Intent()
intent.action = MediaStore.ACTION_IMAGE_CAPTURE
startActivityForResult(intent)

medium

A. Intent action should be set using setAction() method

B. Missing request code parameter in startActivityForResult

C. Intent should be created with MediaStore.ACTION_IMAGE_CAPTURE in constructor

D. startActivityForResult cannot be used to launch camera

Solution

1. Step 1: Check startActivityForResult usage

   This method requires two parameters: an Intent and a request code integer.

2. Step 2: Identify missing parameter

   The code calls startActivityForResult with only the Intent, missing the request code.

3. Final Answer:

   Missing request code parameter in startActivityForResult -> Option B

4. Quick Check:

   startActivityForResult needs Intent + request code [OK]

Hint: Always pass request code with Intent in startActivityForResult [OK]

Common Mistakes:

• Omitting request code parameter
• Using wrong Intent constructor
• Misunderstanding startActivityForResult signature

5. You want to save a full-size photo taken by the camera to a file in your app. Which approach correctly combines camera intent and file handling in Kotlin?

hard

A. Save photo by reading camera app cache directory after intent finishes

B. Start camera intent without extras, then save thumbnail from data extras

C. Create a file URI, pass it with Intent extra MediaStore.EXTRA_OUTPUT, then start camera intent

D. Use MediaStore.ACTION_VIDEO_CAPTURE intent to save photo file

Solution

1. Step 1: Understand full-size photo saving

   To save a full-size photo, you must provide a file URI where the camera app saves the image.

2. Step 2: Use Intent extra MediaStore.EXTRA_OUTPUT

   Pass the file URI as an extra in the camera intent using MediaStore.EXTRA_OUTPUT before starting the intent.

3. Step 3: Start camera intent with this setup

   This ensures the camera saves the full photo to your file, not just a thumbnail in data extras.

4. Final Answer:

   Create a file URI, pass it with Intent extra MediaStore.EXTRA_OUTPUT, then start camera intent -> Option C

5. Quick Check:

   File URI + EXTRA_OUTPUT = full photo saved [OK]

Hint: Use EXTRA_OUTPUT with file URI for full-size photos [OK]

Common Mistakes:

• Relying on thumbnail from data extras only
• Not providing file URI to camera intent
• Using video capture intent for photos