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.