Toggle switch in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a toggle switch in SwiftUI.

iOS Swift

Toggle(isOn: $[1]) {
    Text("Enable feature")
}

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

AisEnabled

BisOn

CtoggleState

DfeatureToggle

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that is not declared as @State.

Forgetting the $ sign before the variable name.

The toggle needs a binding to a @State variable, here named toggleState, to track its on/off state.

2fill in blank

medium

Complete the code to declare a state variable for the toggle switch.

iOS Swift

@State private var [1] = false

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

AtoggleState

BisOn

CswitchValue

DfeatureEnabled

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name different from the one bound to the toggle.

Not marking the variable with @State.

The variable toggleState is used to track the toggle's state and must be declared with @State.

3fill in blank

hard

Fix the error in the toggle binding by completing the code.

iOS Swift

Toggle(isOn: [1]) {
    Text("Notifications")
}

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

A$toggleState

BtoggleState

C*toggleState

D&toggleState

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the variable without $ causes a type error.

Using & or * are not valid in SwiftUI bindings.

The toggle requires a binding, so the variable must be prefixed with $ to pass a binding.

4fill in blank

hard

Fill both blanks to create a toggle with a label and a state variable.

iOS Swift

@State private var [1] = false

Toggle(isOn: $[2]) {
    Text("Dark Mode")
}

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

AdarkModeEnabled

BdarkMode

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in declaration and binding.

Forgetting the $ in the binding.

The state variable name must be consistent in declaration and binding. Here, darkModeEnabled is used.

5fill in blank

hard

Fill all three blanks to create a toggle that updates a text label based on its state.

iOS Swift

@State private var [1] = false

var body: some View {
    VStack {
        Toggle(isOn: $[2]) {
            Text("Airplane Mode")
        }
        Text([3] ? "On" : "Off")
    }
}

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

AairplaneMode

DisOn

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in different places.

Not using the variable in the text ternary expression.

The same state variable airplaneMode is declared, bound to the toggle, and used to show the text status.

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