Cloud Storage in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize a reference to the Firebase Storage root.

iOS Swift

let storage = Storage.storage()
let storageRef = storage.[1]

Drag options to blanks, or click blank then click option'

Areference()

Bref()

CrootReference()

Droot()

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ref()' instead of 'reference()'.

Trying to use 'root()' which does not exist.

The correct method to get the root reference of Firebase Storage is reference().

2fill in blank

medium

Complete the code to upload data to a file named "image.jpg" in Firebase Storage.

iOS Swift

let data = Data()
let imageRef = storageRef.child("[1]")
imageRef.putData(data, metadata: nil) { metadata, error in
  // handle completion
}

Drag options to blanks, or click blank then click option'

Aphoto.jpg

Bpicture.png

Cimage.jpg

Dimage.png

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'image.png' instead of 'image.jpg'.

Using a different file name like 'photo.jpg'.

The file name to upload is 'image.jpg' as specified in the instruction.

3fill in blank

hard

Fix the error in the code to download data from Firebase Storage with a maximum size of 1MB.

iOS Swift

let imageRef = storageRef.child("image.jpg")
imageRef.getData(maxSize: [1]) { data, error in
  if let data = data {
    // use data
  }
}

Drag options to blanks, or click blank then click option'

A1024

B1024 * 1024

C1000000

D1_000_000_000

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1024 which is only 1KB.

Using 1_000_000 which is close but not exact bytes.

The maxSize parameter expects bytes. 1MB equals 1024 * 1024 bytes.

4fill in blank

hard

Fill both blanks to create a dictionary of file names and their sizes in bytes from metadata.

iOS Swift

var fileSizes = [String: Int64]()
for item in items {
  item.getMetadata { metadata, error in
    if let metadata = metadata {
      fileSizes[[1]] = metadata.[2]
    }
  }
}

Drag options to blanks, or click blank then click option'

Aitem.name

Bitem.fullPath

Csize

DtotalBytes

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'item.fullPath' instead of 'item.name' for the file name.

Using 'totalBytes' instead of 'size' for the file size.

The file name is accessed by item.name and the size in bytes is metadata.size.

5fill in blank

hard

Fill all three blanks to delete a file named "oldfile.txt" from Firebase Storage and handle errors.

iOS Swift

let oldFileRef = storageRef.child("[1]")
oldFileRef.[2] { error in
  if let error = error {
    print("Failed to delete: \(error.localizedDescription)")
  } else {
    print("[3]")
  }
}

Drag options to blanks, or click blank then click option'

Aoldfile.txt

Bdelete(completion:)

Cdelete

DFile deleted successfully

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'delete(completion:)' which is not the correct method call syntax.

Using a wrong file name or success message.

The file name is 'oldfile.txt', the method to delete is 'delete', and the success message is 'File deleted successfully'.

Practice

1.

What is the main purpose of Cloud Storage in an iOS app?

easy

A. To create user interface elements

B. To store app settings locally on the device

C. To save files online for easy access and sharing

D. To manage app navigation flow

Solution

1. Step 1: Understand Cloud Storage role

   Cloud Storage is designed to save files online so users can access and share them easily.

2. Step 2: Compare options

   Options B, C, and D describe other app functions unrelated to Cloud Storage.

3. Final Answer:

   To save files online for easy access and sharing -> Option C

4. Quick Check:

   Cloud Storage = Online file saving [OK]

Hint: Cloud Storage means saving files online, not local data [OK]

Common Mistakes:

• Confusing Cloud Storage with local storage
• Thinking it manages UI or navigation
• Assuming it stores app settings only

2.

Which of the following is the correct way to create a reference to a file named image.png in Firebase Cloud Storage using Swift?

let storage = Storage.storage()
let storageRef = ...

easy

A. storageRef = storage.child("image.png")

B. storageRef = storage.reference().child("image.png")

C. storageRef = Storage.reference("image.png")

D. storageRef = storage.reference("image.png")

Solution

1. Step 1: Recall Firebase Storage syntax

   To get a reference, use storage.reference() then child("filename") to point to the file.

2. Step 2: Check each option

   storageRef = storage.reference().child("image.png") correctly chains reference() and child(). Options B, C, and D use incorrect method calls or syntax.

3. Final Answer:

   storageRef = storage.reference().child("image.png") -> Option B

4. Quick Check:

   Use reference().child() to get file reference [OK]

Hint: Use reference().child("filename") to get file reference [OK]

Common Mistakes:

• Calling child() directly on storage
• Using Storage.reference() instead of storage.reference()
• Passing filename directly to reference()

3.

What will be printed if the following Swift code successfully uploads a file to Firebase Storage?

let storageRef = Storage.storage().reference().child("file.txt")
let localFile = URL(fileURLWithPath: "/path/to/file.txt")
storageRef.putFile(from: localFile, metadata: nil) { metadata, error in
  if let error = error {
    print("Upload failed: \(error.localizedDescription)")
  } else {
    print("Upload succeeded")
  }
}

medium

A. Upload succeeded

B. Upload failed: File not found

C. Upload failed: Network error

D. No output

Solution

1. Step 1: Analyze the completion handler

   The closure checks if error is nil; if so, it prints "Upload succeeded".

2. Step 2: Given successful upload

   Since upload is successful, error is nil, so the else block runs printing "Upload succeeded".

3. Final Answer:

   Upload succeeded -> Option A

4. Quick Check:

   Success means error is nil, print "Upload succeeded" [OK]

Hint: If error is nil, upload succeeded message prints [OK]

Common Mistakes:

• Assuming error is always non-nil
• Confusing success and failure blocks
• Ignoring the asynchronous completion handler

4.

Identify the error in this Swift code snippet for uploading a file to Firebase Storage:

let storageRef = Storage.storage().reference().child("doc.pdf")
let fileURL = URL(string: "/documents/doc.pdf")!
storageRef.putFile(from: fileURL, metadata: nil) { metadata, error in
  if error != nil {
    print("Upload error")
  } else {
    print("Upload complete")
  }
}

medium

A. Using URL(string:) instead of URL(fileURLWithPath:)

B. Missing metadata parameter in putFile

C. Incorrect child path syntax

D. No completion handler provided

Solution

1. Step 1: Check URL creation method

   URL(string:) is for web URLs; local file paths need URL(fileURLWithPath:).

2. Step 2: Identify impact

   Using URL(string:) with a local path returns nil or incorrect URL, causing upload failure.

3. Final Answer:

   Using URL(string:) instead of URL(fileURLWithPath:) -> Option A

4. Quick Check:

   Local file URLs need URL(fileURLWithPath:) [OK]

Hint: Use URL(fileURLWithPath:) for local file paths [OK]

Common Mistakes:

• Using URL(string:) for local files
• Forgetting to unwrap optional URLs safely
• Ignoring completion handler errors

5.

You want to upload multiple images to Firebase Cloud Storage and keep track of their download URLs for later use. Which approach correctly handles this in Swift?

let images = [URL(fileURLWithPath: "/img1.png"), URL(fileURLWithPath: "/img2.png")]
var downloadURLs: [URL] = []
for imageURL in images {
  let ref = Storage.storage().reference().child(imageURL.lastPathComponent)
  ref.putFile(from: imageURL, metadata: nil) { metadata, error in
    if error == nil {
      ref.downloadURL { url, error in
        if let url = url {
          downloadURLs.append(url)
        }
      }
    }
  }
}
print(downloadURLs)

hard

A. The code will cause a syntax error due to missing await

B. This code correctly prints all download URLs immediately

C. The code uploads files but does not get download URLs

D. This code may print an empty array because uploads are asynchronous

Solution

1. Step 1: Understand asynchronous behavior

   Uploads and downloadURL calls run asynchronously, so print(downloadURLs) runs before completion.

2. Step 2: Effect on printed output

   Because of async calls, downloadURLs is likely empty when printed immediately after the loop.

3. Final Answer:

   This code may print an empty array because uploads are asynchronous -> Option D

4. Quick Check:

   Async uploads delay URL collection, print runs too early [OK]

Hint: Async calls need completion before using results [OK]

Common Mistakes:

• Expecting synchronous behavior from async uploads
• Printing results before upload completion
• Not using dispatch groups or async-await to wait