Toggle switch in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Toggle switch state change effect

What will be the text displayed in the label after toggling the switch from OFF to ON?

iOS Swift

import SwiftUI

struct ContentView: View {
  @State private var isOn = false

  var body: some View {
    VStack {
      Toggle("Enable Feature", isOn: $isOn)
      Text(isOn ? "Feature is ON" : "Feature is OFF")
    }
    .padding()
  }
}

A Toggle is enabled

B Feature is OFF

C Feature is ON

D No text is displayed

💡 Hint

The label text changes based on the toggle's boolean state.

The toggle changes the isOn state from false to true. The Text view shows "Feature is ON" when isOn is true.

❓ lifecycle

intermediate

Toggle switch initial state in UIKit

In UIKit, if you create a UISwitch programmatically and do not set its state, what is the default state of the switch when it appears?

A Random state each time

B OFF (false)

C Undefined, causes a crash

D ON (true)

💡 Hint

Think about the default boolean value for UISwitch's isOn property.

UISwitch defaults to OFF (isOn = false) if not explicitly set.

📝 Syntax

advanced

Correct SwiftUI Toggle binding syntax

Which option correctly binds a Toggle to a @State variable named isEnabled?

iOS Swift

import SwiftUI

struct MyView: View {
  @State private var isEnabled = false

  var body: some View {
    // Toggle code here
  }
}

A Toggle("Enable", isOn: $isEnabled)

B Toggle("Enable", isOn: Binding(isEnabled))

C Toggle("Enable", isOn: isEnabled)

D Toggle("Enable", isOn: Binding($isEnabled))

💡 Hint

Use the $ prefix to pass a binding to the Toggle.

The $ prefix creates a binding to the @State variable, which Toggle requires.

🔧 Debug

advanced

Why does the UISwitch not update the label?

Given this UIKit code, why does the label not update when the switch is toggled? let toggle = UISwitch() let label = UILabel() func setup() { toggle.addTarget(self, action: #selector(switchChanged), for: .valueChanged) } @objc func switchChanged() { label.text = toggle.isOn ? "ON" : "OFF" } // toggle and label are added to the view What is the most likely reason?

A The addTarget method is called after the switch is toggled

B The switchChanged method is not marked @objc

C The toggle's isOn property does not change automatically

D The label is not added to the view hierarchy

💡 Hint

If the label is not visible, text changes won't show.

If the label is not added to the view, updating its text has no visible effect.

🧠 Conceptual

expert

Accessibility for Toggle switches

Which practice best improves accessibility for a toggle switch in SwiftUI?

A Add .accessibilityLabel("Enable feature") to the Toggle

B Use a Text view instead of Toggle for better screen reader support

C Disable the toggle to prevent accidental changes

D Set the toggle color to red for visibility

💡 Hint

Accessibility labels help screen readers describe controls.

Adding .accessibilityLabel provides a clear description for users relying on assistive technologies.

Practice

1. What does a UISwitch control in an iOS app?

easy

A. It lets users toggle between on and off states.

B. It displays a list of options to select from.

C. It shows a progress bar for tasks.

D. It opens a new screen when tapped.

Solution

1. Step 1: Understand the purpose of UISwitch

   A UISwitch is designed to let users turn a setting on or off with a simple tap.

2. Step 2: Compare with other UI controls

   Unlike lists or progress bars, UISwitch specifically toggles between two states: on and off.

3. Final Answer:

   It lets users toggle between on and off states. -> Option A

4. Quick Check:

   UISwitch = toggle on/off [OK]

Hint: UISwitch always toggles between two states [OK]

Common Mistakes:

• Confusing UISwitch with buttons that open new screens
• Thinking UISwitch shows progress or lists
• Assuming UISwitch can select multiple options

2. Which of the following is the correct way to create a UISwitch in Swift?

easy

A. let toggle = UISwitch.new()

B. let toggle = Switch()

C. let toggle = UISwitch()

D. let toggle = UISwitch.create()

Solution

1. Step 1: Recall UISwitch initialization syntax

   In Swift, UI elements like UISwitch are created by calling their initializer with parentheses.

2. Step 2: Check each option

   Only UISwitch() is the correct initializer. The others use invalid methods or class names.

3. Final Answer:

   let toggle = UISwitch() -> Option C

4. Quick Check:

   Initialize UISwitch with UISwitch() [OK]

Hint: Use parentheses to create UISwitch instance [OK]

Common Mistakes:

• Using incorrect class name like Switch
• Trying to call .new() or .create() methods
• Omitting parentheses when creating UISwitch

3. What will be printed when this Swift code runs?

let toggle = UISwitch()
toggle.isOn = true
print(toggle.isOn)

medium

A. Compilation error

B. false

C. nil

D. true

Solution

1. Step 1: Understand the isOn property

   The isOn property of UISwitch indicates if the switch is on (true) or off (false).

2. Step 2: Analyze the code

   The code sets toggle.isOn = true and then prints toggle.isOn, so it will print true.

3. Final Answer:

   true -> Option D

4. Quick Check:

   Setting isOn true prints true [OK]

Hint: Print isOn after setting it to see true/false [OK]

Common Mistakes:

• Assuming default is false without setting
• Confusing isOn with other properties
• Expecting nil or error from print

4. Identify the error in this Swift code that tries to detect switch changes:

let toggle = UISwitch()
toggle.addTarget(self, action: #selector(switchChanged), for: .valueChanged)

@objc func switchChanged() {
    print("Switch toggled")
}

medium

A. Wrong event type used in addTarget

B. Missing parameter in switchChanged method

C. UISwitch cannot use addTarget

D. Missing UISwitch initialization

Solution

1. Step 1: Check addTarget usage

   The addTarget method requires the action method to accept the sender parameter.

2. Step 2: Analyze switchChanged method signature

   The method switchChanged() has no parameters but should accept _ sender: UISwitch.

3. Final Answer:

   Missing parameter in switchChanged method -> Option B

4. Quick Check:

   Action method needs sender parameter [OK]

Hint: Action methods need sender parameter for addTarget [OK]

Common Mistakes:

• Omitting sender parameter in action method
• Using wrong event type like .touchUpInside
• Thinking UISwitch can't use addTarget

5. You want to create a toggle switch that updates a label text to "ON" or "OFF" when toggled. Which code snippet correctly implements this behavior?

let toggle = UISwitch()
let label = UILabel()

// Which switchChanged method is correct?

hard

A. @objc func switchChanged(_ sender: UISwitch) {
label.text = sender.isOn ? "ON" : "OFF"
}

B. @objc func switchChanged() {
label.text = toggle.isOn ? "ON" : "OFF"
}

C. @objc func switchChanged(_ sender: UISwitch) {
if sender.isOn == false {
label.text = "ON"
} else {
label.text = "OFF"
}
}

D. @objc func switchChanged(_ sender: UISwitch) {
label.text = "ON"
}

Solution

1. Step 1: Check method signature and parameter

   The action method must accept the sender UISwitch to get its current state.

2. Step 2: Verify label text update logic

   @objc func switchChanged(_ sender: UISwitch) { label.text = sender.isOn ? "ON" : "OFF" } uses a ternary operator to set label text to "ON" if switch is on, else "OFF", which is correct.

3. Step 3: Review other options

   @objc func switchChanged() { label.text = toggle.isOn ? "ON" : "OFF" } lacks sender parameter; @objc func switchChanged(_ sender: UISwitch) { if sender.isOn == false { label.text = "ON" } else { label.text = "OFF" } } reverses ON/OFF logic; @objc func switchChanged(_ sender: UISwitch) { label.text = "ON" } always sets "ON" ignoring switch state.

4. Final Answer:

   @objc func switchChanged(_ sender: UISwitch) { label.text = sender.isOn ? "ON" : "OFF" } -> Option A

5. Quick Check:

   Use sender.isOn with ternary to update label [OK]

Hint: Use sender.isOn ? "ON" : "OFF" to update label [OK]

Common Mistakes:

• Forgetting sender parameter in action method
• Reversing ON and OFF text logic
• Ignoring switch state and setting fixed text