List with ForEach in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What will this SwiftUI List display?

Consider this SwiftUI code snippet. What will the List show when the app runs?

iOS Swift

struct ContentView: View {
  let fruits = ["Apple", "Banana", "Cherry"]
  var body: some View {
    List {
      ForEach(fruits, id: \.self) { fruit in
        Text(fruit)
      }
    }
  }
}

A A list showing numbers 0, 1, 2 instead of fruit names.

B A list showing Apple, Banana, and Cherry as separate rows.

C A list showing only Apple because ForEach stops after first item.

D The code will not compile due to missing id parameter.

💡 Hint

Think about what ForEach does with an array and the id parameter.

ForEach iterates over the fruits array and creates a Text view for each fruit. The id: \.self tells SwiftUI to use the string itself as a unique identifier. So the List shows Apple, Banana, and Cherry each on its own row.

📝 Syntax

intermediate

Identify the syntax error in this ForEach usage

Which option correctly fixes the syntax error in this SwiftUI code?

iOS Swift

struct ContentView: View {
  let numbers = [1, 2, 3]
  var body: some View {
    List {
      ForEach(numbers) { number in
        Text("\(number)")
      }
    }
  }
}

A Remove the closure parameter: ForEach(numbers) { Text("\(number)") }

B Change numbers to a Set: ForEach(Set(numbers)) { number in ... }

C Add id: \.self to ForEach: ForEach(numbers, id: \.self) { number in ... }

D Replace List with VStack: VStack { ForEach(numbers) { number in ... } }

💡 Hint

ForEach needs a way to identify each item uniquely when using simple arrays.

When using ForEach with an array of simple values like Int, you must provide an id parameter to uniquely identify each element. Adding id: \.self fixes the syntax error.

❓ lifecycle

advanced

What happens if the data array changes in a ForEach List?

If the array used in ForEach changes (items added or removed), what does SwiftUI do to the List?

A SwiftUI updates the List to reflect the new array contents automatically.

B The List does not update until the app restarts.

C The List duplicates old and new items causing visual glitches.

D SwiftUI crashes because ForEach cannot handle dynamic data.

💡 Hint

Think about how SwiftUI reacts to state changes.

SwiftUI watches the data used in ForEach. When the array changes, SwiftUI updates the List UI automatically to match the new data.

🔧 Debug

advanced

Why does this ForEach cause a runtime crash?

This code crashes at runtime. What is the cause?

iOS Swift

struct ContentView: View {
  let items = ["A", "B", "A"]
  var body: some View {
    List {
      ForEach(items, id: \.self) { item in
        Text(item)
      }
    }
  }
}

A The array has duplicate items used as id, causing duplicate id error.

B ForEach cannot use strings as id, only integers.

C List requires a section header, missing here.

D Text views must have unique tags, missing here.

💡 Hint

Check the uniqueness of the id values.

Using id: \.self means each item must be unique. The array has two "A" strings, causing duplicate id error and crash.

🧠 Conceptual

expert

Why use ForEach inside a List instead of just List with data?

Which reason best explains why developers use ForEach inside a List in SwiftUI?

A Using ForEach inside List is required to enable scrolling.

B List cannot display arrays directly without ForEach.

C ForEach improves app performance by caching views automatically.

D ForEach allows more control over each row’s view and supports complex layouts inside List.

💡 Hint

Think about flexibility in building UI rows.

ForEach lets you customize each row’s content and layout inside a List. List alone can display simple data but ForEach is needed for complex or dynamic row views.