Camera and photo library in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens when UIImagePickerController sourceType is set to .camera?

Consider this Swift code snippet in an iOS app:

let picker = UIImagePickerController()
picker.sourceType = .camera
present(picker, animated: true)

What will the user see after this code runs?

iOS Swift

let picker = UIImagePickerController()
picker.sourceType = .camera
present(picker, animated: true)

A The app shows an error because .camera is not a valid sourceType.

B The app opens the photo library for the user to select an existing photo.

C The app opens the device camera interface allowing the user to take a photo.

D The app opens a blank screen with no controls.

💡 Hint

Think about what .camera means in UIImagePickerController.

Setting sourceType to .camera tells the app to open the device's camera interface so the user can take a new photo.

🧠 Conceptual

intermediate

Why must you check UIImagePickerController.isSourceTypeAvailable before using .camera?

In iOS development, before setting UIImagePickerController's sourceType to .camera, why should you check if the camera is available using isSourceTypeAvailable(.camera)?

A Because some devices or simulators do not have a camera, and trying to use it without checking causes a crash.

B Because it automatically requests camera permission from the user.

C Because it improves app performance by preloading the camera hardware.

D Because it changes the camera resolution settings.

💡 Hint

Think about devices like iPads without cameras or simulators.

Not all devices have a camera. Checking availability prevents the app from crashing when trying to access a missing camera.

❓ lifecycle

advanced

What delegate method is called after a user picks a photo from the library?

When using UIImagePickerController to let the user pick a photo from the photo library, which delegate method is called after the user selects a photo?

A imagePickerController(_:didFinishPickingMediaWithInfo:)

B imagePickerControllerDidCancel(_:)

C applicationDidBecomeActive(_:)

D viewDidLoad()

💡 Hint

This method provides the selected image info.

The delegate method imagePickerController(_:didFinishPickingMediaWithInfo:) is called when the user finishes picking a photo.

🔧 Debug

advanced

Why does this code crash when accessing the photo library?

Given this Swift code snippet:

let picker = UIImagePickerController()
picker.sourceType = .photoLibrary
present(picker, animated: true)

The app crashes on devices running iOS 14 or later. What is the most likely cause?

iOS Swift

let picker = UIImagePickerController()
picker.sourceType = .photoLibrary
present(picker, animated: true)

A The present method requires a completion handler.

B The sourceType .photoLibrary is not supported on iOS 14 or later.

C UIImagePickerController must be presented inside a navigation controller.

D The app is missing the NSPhotoLibraryUsageDescription key in Info.plist, so iOS denies access.

💡 Hint

Check app permissions in Info.plist.

iOS requires a usage description key in Info.plist to allow photo library access. Missing it causes a crash.

❓ navigation

expert

What is the correct way to dismiss UIImagePickerController after photo selection?

After the user picks a photo using UIImagePickerController, which code snippet correctly dismisses the picker and processes the image?

iOS Swift

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
    // process image
}

A dismiss(animated: true) { /* process image here */ }

B picker.dismiss(animated: true) { /* process image here */ }

C picker.popViewController(animated: true)

D self.navigationController?.dismiss(animated: true)

💡 Hint

Dismiss the picker itself, not the whole view controller.

You must call dismiss on the picker to close it, optionally handling image processing in the completion block.

Practice

1. What is the purpose of setting sourceType to .camera in UIImagePickerController?

easy

A. To select an existing photo from the photo library

B. To record a video using the device camera

C. To allow the user to take a new photo using the device camera

D. To open the device settings

Solution

1. Step 1: Understand sourceType usage

   The sourceType property of UIImagePickerController defines where the image will come from.

2. Step 2: Identify the effect of .camera

   Setting sourceType to .camera opens the device camera to take a new photo.

3. Final Answer:

   To allow the user to take a new photo using the device camera -> Option C

4. Quick Check:

   sourceType = .camera means take new photo [OK]

Hint: Camera sourceType means take a new photo [OK]

Common Mistakes:

• Confusing .camera with .photoLibrary
• Thinking .camera records video by default
• Assuming .camera opens settings

2. Which of the following is the correct way to declare a UIImagePickerController and set its delegate in Swift?

easy

A. var picker = UIImagePickerController()
picker.delegate = self()

B. let picker = UIImagePickerController()
picker.delegate = self

C. let picker = UIImagePickerController
picker.delegate = self()

D. var picker = UIImagePickerController
picker.delegate = self

Solution

1. Step 1: Correct initialization syntax

   In Swift, UIImagePickerController() requires parentheses to create an instance.

2. Step 2: Assign delegate properly

   The delegate is assigned as self without parentheses because it is a property, not a function call.

3. Final Answer:

   let picker = UIImagePickerController() picker.delegate = self -> Option B

4. Quick Check:

   Initialize with () and assign delegate without () [OK]

Hint: Use parentheses for init, no parentheses for delegate [OK]

Common Mistakes:

• Forgetting parentheses when creating UIImagePickerController
• Using parentheses when assigning delegate
• Declaring picker without parentheses

3. Given the following code snippet, what will be printed when a user selects a photo from the library?

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
    if let image = info[.originalImage] as? UIImage {
        print("Image selected")
    } else {
        print("No image found")
    }
}

medium

A. Nothing is printed

B. No image found

C. Compilation error

D. Image selected

Solution

1. Step 1: Check the delegate method behavior

   The method imagePickerController(_:didFinishPickingMediaWithInfo:) is called after user picks a photo.

2. Step 2: Understand the info dictionary

   The info dictionary contains the key .originalImage with the selected UIImage if successful.

3. Final Answer:

   Image selected -> Option D

4. Quick Check:

   Image exists in info dictionary after selection [OK]

Hint: If image exists in info, print "Image selected" [OK]

Common Mistakes:

• Assuming image is nil after selection
• Confusing delegate method names
• Not casting info dictionary value properly

4. What is the error in the following Swift code that prevents the image picker from working correctly?

let picker = UIImagePickerController()
picker.sourceType = .camera
picker.delegate = self
present(picker, animated: true)

medium

A. Missing UIImagePickerControllerDelegate and UINavigationControllerDelegate conformance

B. Incorrect sourceType value

C. Delegate should be assigned after presenting picker

D. Cannot present picker without a navigation controller

Solution

1. Step 1: Check delegate conformance requirements

   To use UIImagePickerController delegate methods, the class must conform to UIImagePickerControllerDelegate and UINavigationControllerDelegate.

2. Step 2: Identify missing conformance

   If the class does not conform, delegate methods won't be called and picker won't work properly.

3. Final Answer:

   Missing UIImagePickerControllerDelegate and UINavigationControllerDelegate conformance -> Option A

4. Quick Check:

   Delegate protocols must be adopted for picker to work [OK]

Hint: Always conform to both delegate protocols [OK]

Common Mistakes:

• Forgetting to add delegate protocols to class
• Assigning delegate after presenting picker
• Using wrong sourceType value

5. You want to allow users to either take a new photo or pick one from their library. Which approach correctly handles both options in Swift?

hard

A. Set sourceType dynamically based on user choice, then present a single UIImagePickerController

B. Use sourceType = .savedPhotosAlbum to cover both camera and library

C. Create two UIImagePickerController instances, one with .camera and one with .photoLibrary, and present both simultaneously

D. Use UIImagePickerController only for camera and a custom UI for photo library

Solution

1. Step 1: Understand sourceType flexibility

   A single UIImagePickerController can have its sourceType set to either .camera or .photoLibrary before presenting.

2. Step 2: Handle user choice before presenting picker

   Based on user selection, set the sourceType dynamically and present the picker once.

3. Final Answer:

   Set sourceType dynamically based on user choice, then present a single UIImagePickerController -> Option A

4. Quick Check:

   One picker, sourceType changes per user choice [OK]

Hint: Use one picker, change sourceType before presenting [OK]

Common Mistakes:

• Trying to present two pickers at once
• Using savedPhotosAlbum to cover camera
• Mixing custom UI unnecessarily