SwiftUI uses result builders - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this SwiftUI View code?

Consider this SwiftUI view using a result builder to create a VStack. What text will be shown on the screen?

Swift

import SwiftUI

struct ContentView: View {
    var body: some View {
        VStack {
            Text("Hello")
            Text("World")
        }
    }
}

// Assume this is run in a SwiftUI preview or app

A A vertical stack showing two lines: "Hello" on top and "World" below

B A horizontal stack showing "Hello World" on the same line

C An empty view with no text displayed

D A runtime error because VStack requires explicit closure syntax

💡 Hint

Think about what VStack does and how result builders let you list views inside it.

VStack arranges views vertically. The result builder lets you list multiple views inside the closure, so Text("Hello") and Text("World") appear stacked vertically.

🧠 Conceptual

intermediate

What role do result builders play in SwiftUI?

Which statement best describes how SwiftUI uses result builders?

A They replace the need for any closures in SwiftUI

B They automatically generate UI code from JSON data

C They are used to handle asynchronous network calls in SwiftUI

D They allow writing multiple views inside a closure that are combined into one view container

💡 Hint

Think about how SwiftUI lets you list views inside containers like VStack.

Result builders let you write multiple child views inside a closure, and SwiftUI combines them into a single container view like VStack or HStack.

🔧 Debug

advanced

Why does this SwiftUI code cause a compile error?

Examine this SwiftUI code snippet. Why does it fail to compile?

Swift

import SwiftUI

struct ContentView: View {
    var body: some View {
        VStack {
            if true {
                Text("Visible")
            } else {
            }
            Text("Always here")
        }
    }
}

A Because the else block is missing a return statement

B Because the if-else inside VStack is not allowed without an explicit return type in result builders

C Because Text views must be wrapped in Group when used conditionally

D Because VStack cannot contain conditional statements

💡 Hint

Think about how result builders handle conditional branches inside view containers.

SwiftUI's result builder requires all branches of an if-else to produce the same type. Without explicit typing or using Group, the compiler cannot infer the combined type, causing an error.

📝 Syntax

advanced

Which option correctly uses a result builder in SwiftUI?

Choose the code snippet that correctly uses a result builder to create a view with two Text elements.

A VStack { Text("One") ; Text("Two") }

B VStack { Text("One") Text("Two") ; }

C VStack { Text("One") Text("Two") }

D VStack { Text("One") , Text("Two") }

💡 Hint

Remember how Swift separates statements inside closures.

In Swift closures, statements must be separated by semicolons or newlines. Option A correctly separates the two Text views with a semicolon.

🚀 Application

expert

How many views are created by this SwiftUI code using result builders?

Given this SwiftUI code, how many Text views will be created and displayed?

Swift

import SwiftUI

struct ContentView: View {
    var body: some View {
        VStack {
            ForEach(0..<3) { i in
                if i % 2 == 0 {
                    Text("Even: \(i)")
                } else {
                    Text("Odd: \(i)")
                }
            }
        }
    }
}

A 2

B 1

C 3

D 0

💡 Hint

Count how many times the loop runs and what views it creates each time.

The ForEach runs 3 times (0,1,2). Each iteration creates one Text view, so total 3 Text views are created.

Practice

1. What is the main purpose of using @ViewBuilder in SwiftUI?

easy

A. To handle network requests

B. To create animations automatically

C. To combine multiple views inside a closure cleanly

D. To manage data persistence

Solution

1. Step 1: Understand the role of @ViewBuilder

   @ViewBuilder is a result builder that allows combining multiple views inside a closure.

2. Step 2: Identify its main use in SwiftUI

   It helps write clean and readable UI code by letting you list views without extra syntax.

3. Final Answer:

   To combine multiple views inside a closure cleanly -> Option C

4. Quick Check:

   @ViewBuilder combines views [OK]

Hint: Remember: @ViewBuilder builds multiple views together [OK]

Common Mistakes:

• Confusing @ViewBuilder with animation or data tasks
• Thinking it manages data or network
• Assuming it creates views automatically without code

2. Which of the following is the correct way to declare a function using @ViewBuilder in SwiftUI?

easy

A. func buildView() -> some View { ... }

B. func buildView() -> @ViewBuilder some View { ... }

C. func buildView() @ViewBuilder -> some View { ... }

D. @ViewBuilder func buildView() -> some View { ... }

Solution

1. Step 1: Recall the syntax for using @ViewBuilder

   The attribute @ViewBuilder is placed before the function declaration.

2. Step 2: Check each option's syntax

   @ViewBuilder func buildView() -> some View { ... } correctly places @ViewBuilder before the function name. Others misuse placement.

3. Final Answer:

   @ViewBuilder func buildView() -> some View { ... } -> Option D

4. Quick Check:

   @ViewBuilder goes before func [OK]

Hint: Put @ViewBuilder right before the function keyword [OK]

Common Mistakes:

• Placing @ViewBuilder after the function name or return type
• Using it as a return type modifier
• Omitting @ViewBuilder when combining views

3. What will be the output of this SwiftUI code snippet using @ViewBuilder?

struct ContentView: View {
    @ViewBuilder
    func buildContent() -> some View {
        Text("Hello")
        Text("World")
    }
    var body: some View {
        buildContent()
    }
}

medium

A. Displays "Hello" and "World" stacked vertically

B. Displays only "World" text

C. Compilation error due to missing container view

D. Displays "HelloWorld" as a single text

Solution

1. Step 1: Understand @ViewBuilder behavior

   @ViewBuilder allows multiple views to be returned as a combined view, typically stacked vertically.

2. Step 2: Analyze the code output

   The two Text views "Hello" and "World" will be combined and shown one after another vertically.

3. Final Answer:

   Displays "Hello" and "World" stacked vertically -> Option A

4. Quick Check:

   Multiple views combined = stacked display [OK]

Hint: Multiple views in @ViewBuilder stack vertically by default [OK]

Common Mistakes:

• Thinking only last view shows
• Expecting a single concatenated text
• Assuming compilation error without explicit container

4. Identify the error in this SwiftUI code using @ViewBuilder:

struct MyView: View {
    @ViewBuilder
    func content() -> some View {
        if Bool.random() {
            Text("Yes")
        } else {
            Text("No")
        }
        Text("Always")
    }
    var body: some View {
        content()
    }
}

medium

A. Cannot have multiple views after conditional without grouping

B. Missing return keyword in function

C. Cannot use Bool.random() inside @ViewBuilder

D. Function must return a single Text view

Solution

1. Step 1: Understand @ViewBuilder rules with conditionals

   When using conditionals inside @ViewBuilder, all branches must return views, but multiple views after conditionals need grouping.

2. Step 2: Identify the problem in code

   The code has an if-else returning one Text each, then another Text outside. This causes multiple views at the same level without grouping, which is invalid.

3. Final Answer:

   Cannot have multiple views after conditional without grouping -> Option A

4. Quick Check:

   Multiple views after if-else need grouping [OK]

Hint: Group multiple views after conditionals inside a container [OK]

Common Mistakes:

• Ignoring need for grouping multiple views after if-else
• Thinking Bool.random() causes error
• Assuming return keyword is mandatory in @ViewBuilder functions

5. How can you modify this @ViewBuilder function to correctly return multiple views including a conditional view?

@ViewBuilder
func build() -> some View {
    Text("Start")
    if showExtra {
        Text("Extra")
    }
    Text("End")
}

Assuming showExtra is a Boolean variable.

hard

A. Remove the if condition and always show "Extra"

B. Wrap all views inside a VStack to group them

C. Return an array of views instead of using @ViewBuilder

D. Use multiple @ViewBuilder functions for each view

Solution

1. Step 1: Recognize the problem with multiple views and conditionals

   Multiple views including conditionals must be grouped inside a container view like VStack to form a single combined view.

2. Step 2: Apply grouping to fix the function

   Wrapping all views inside VStack { ... } groups them and allows conditional views without errors.

3. Final Answer:

   Wrap all views inside a VStack to group them -> Option B

4. Quick Check:

   Group views with container like VStack [OK]

Hint: Use VStack to group multiple views with conditionals [OK]

Common Mistakes:

• Trying to return multiple views without grouping
• Removing conditionals instead of fixing structure
• Returning arrays which is not supported as View