Cloud Storage in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Uploading a File to Cloud Storage

What will happen when this Swift code runs to upload a file to Firebase Storage?

iOS Swift

let storage = Storage.storage()
let storageRef = storage.reference()
let fileURL = URL(string: "https://example.com/image.png")!
let imagesRef = storageRef.child("images/image.png")
imagesRef.putFile(from: fileURL, metadata: nil) { metadata, error in
  if let error = error {
    print("Upload failed: \(error.localizedDescription)")
  } else {
    print("Upload successful")
  }
}

A The file is uploaded to the root of Firebase Storage, ignoring the 'images/' folder.

B The file at the URL is uploaded to the path 'images/image.png' in Firebase Storage, and 'Upload successful' is printed on success.

C The file is uploaded but the completion handler is never called, so no message is printed.

D The code will crash because URL(string:) returns an optional and is not safely unwrapped.

💡 Hint

Check how the URL is created and how the completion handler works.

The code safely unwraps the URL with ! and uploads the file to the specified path. The completion handler prints success or error messages accordingly.

🧠 Conceptual

intermediate

Understanding Cloud Storage Security Rules

Which statement correctly describes Firebase Storage security rules behavior?

A Security rules only apply to Firestore database, not to Firebase Storage.

B Security rules automatically encrypt files on the device before uploading to Firebase Storage.

C Security rules control who can read or write files in Firebase Storage based on authentication and file path.

D Security rules allow anyone to access files unless you manually disable public access in the Firebase console.

💡 Hint

Think about how access is controlled in cloud storage.

Firebase Storage security rules define who can read or write files based on user authentication and file paths. They do not encrypt files or only apply to Firestore.

❓ lifecycle

advanced

Handling Download Task Lifecycle

What is the correct way to pause and resume a download task from Firebase Storage in Swift?

iOS Swift

let storageRef = Storage.storage().reference().child("files/video.mp4")
var downloadTask: StorageDownloadTask?
downloadTask = storageRef.write(toFile: localURL) { url, error in
  if let error = error {
    print("Download failed: \(error.localizedDescription)")
  } else {
    print("Download succeeded")
  }
}
// Later in code
// How to pause and resume the download task?

A Call downloadTask?.pause() to pause and downloadTask?.resume() to resume the download.

B Call downloadTask?.cancel() to pause and create a new downloadTask to resume.

C Call downloadTask?.suspend() to pause and downloadTask?.start() to resume.

D Download tasks cannot be paused or resumed once started.

💡 Hint

Check the StorageDownloadTask API for controlling downloads.

Firebase StorageDownloadTask supports pause() and resume() methods to control the download lifecycle.

🔧 Debug

advanced

Diagnosing a Failed Upload Error

Given this code snippet, what is the most likely cause of the upload failure?

iOS Swift

let storageRef = Storage.storage().reference().child("uploads/photo.jpg")
let data = Data()
storageRef.putData(data, metadata: nil) { metadata, error in
  if let error = error {
    print("Upload error: \(error.localizedDescription)")
  } else {
    print("Upload success")
  }
}

A The data is empty, so the upload fails because there is no content to upload.

B The storage reference path is invalid because it uses a forward slash.

C The metadata parameter is nil, which causes a runtime error.

D The completion handler is missing, so the upload never completes.

💡 Hint

Consider what happens if you upload empty data.

Uploading empty Data() results in no content, which usually causes the upload to fail or be rejected by Firebase Storage.

❓ navigation

expert

Navigating After Cloud Storage Upload Completion

In a SwiftUI app, you want to upload a file to Firebase Storage and then navigate to a 'SuccessView' only after the upload completes successfully. Which approach correctly achieves this?

iOS Swift

struct UploadView: View {
  @State private var uploadComplete = false
  var body: some View {
    VStack {
      if uploadComplete {
        SuccessView()
      } else {
        Button("Upload File") {
          uploadFile()
        }
      }
    }
  }

  func uploadFile() {
    let storageRef = Storage.storage().reference().child("files/data.txt")
    let data = "Hello".data(using: .utf8)!
    storageRef.putData(data, metadata: nil) { metadata, error in
      if error == nil {
        DispatchQueue.main.async {
          uploadComplete = true
        }
      }
    }
  }
}

A You must use a NavigationLink with isActive bound to uploadComplete to navigate properly.

B This code works perfectly and navigates to SuccessView after upload completes.

C The uploadFile function should be marked async and awaited to update uploadComplete correctly.

D This code will not compile because uploadComplete is modified inside a closure without @MainActor or DispatchQueue.main.async.

💡 Hint

Think about updating @State variables from background threads.

Firebase Storage completion handlers run on background threads. Updating @State variables must happen on the main thread, so this code will cause a runtime warning or crash.