Button and action handling in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a button with the title "Press Me".

iOS Swift

let button = UIButton()
button.setTitle([1], for: .normal)

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

A"Button"

B"Click"

C"Tap"

D"Press Me"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the quotes around the title string.

Using the wrong title text.

The button title must be set as a string with quotes, exactly "Press Me".

2fill in blank

medium

Complete the code to add an action to the button that calls the method buttonTapped when pressed.

iOS Swift

button.addTarget(self, action: #selector([1]), for: .touchUpInside)

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

AbuttonTapped

BtapButton

CbuttonPressed

DpressedButton

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that does not exist.

Missing the #selector syntax.

The selector must match the method name exactly, which is buttonTapped.

3fill in blank

hard

Fix the error in the method signature for the button action handler.

iOS Swift

@objc func [1](sender: UIButton) {
    print("Button was tapped")
}

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

AbuttonTap

BbuttonTapped

CbuttonTappedAction

DtapButton

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatch between selector name and method name.

Missing @objc attribute.

The method name must match the selector used when adding the target, which is buttonTapped.

4fill in blank

hard

Fill both blanks to create a button, set its title, and add it to the view.

iOS Swift

let button = UIButton(type: [1])
button.setTitle([2], for: .normal)
view.addSubview(button)

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

A.system

B"Click Me"

C.custom

D"Press"

Attempts:

3 left

💡 Hint

Common Mistakes

Using .custom type without setting appearance.

Forgetting quotes around the title.

Use .system for the button type and "Click Me" as the title string.

5fill in blank

hard

Fill all three blanks to create a button, set its title color, and add an action.

iOS Swift

let button = UIButton(type: [1])
button.setTitleColor([2], for: .normal)
button.addTarget(self, action: #selector([3]), for: .touchUpInside)

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

A.system

BUIColor.blue

CbuttonTapped

D.custom

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong button type.

Forgetting to use UIColor for colors.

Mismatch in action method name.

Use .system for button type, UIColor.blue for title color, and buttonTapped as the action method.

Practice

1. What is the main purpose of a UIButton in an iOS app?

easy

A. To let users tap and trigger actions

B. To display static text only

C. To store data persistently

D. To manage app navigation automatically

Solution

1. Step 1: Understand UIButton role

   A UIButton is a UI element that users can tap to perform an action.

2. Step 2: Compare options with UIButton purpose

   Only To let users tap and trigger actions describes this interaction purpose correctly.

3. Final Answer:

   To let users tap and trigger actions -> Option A

4. Quick Check:

   UIButton = user tap action [OK]

Hint: Buttons are for user taps triggering actions [OK]

Common Mistakes:

• Confusing buttons with labels
• Thinking buttons store data
• Assuming buttons handle navigation automatically

2. Which of the following is the correct way to add an action to a UIButton in Swift?

easy

A. button.onTap = buttonTapped()

B. button.addTarget(self, action: #selector(buttonTapped), for: .touchUpInside)

C. button.addAction(#selector(buttonTapped))

D. button.action = #selector(buttonTapped)

Solution

1. Step 1: Recall UIButton action syntax

   The correct method is addTarget(_:action:for:) with #selector for the method.

2. Step 2: Match syntax with options

   Only button.addTarget(self, action: #selector(buttonTapped), for: .touchUpInside) uses the correct method and parameters.

3. Final Answer:

   button.addTarget(self, action: #selector(buttonTapped), for: .touchUpInside) -> Option B

4. Quick Check:

   addTarget + #selector + .touchUpInside = correct [OK]

Hint: Use addTarget with #selector and .touchUpInside [OK]

Common Mistakes:

• Using nonexistent addAction method
• Assigning action directly without addTarget
• Calling the selector method instead of referencing it

3. Given the code below, what happens when the button is tapped?

let button = UIButton()
button.addTarget(self, action: #selector(showMessage), for: .touchUpInside)

@objc func showMessage() {
    print("Button was tapped")
}

medium

A. The app crashes due to missing button title

B. Nothing happens because the method is missing @objc

C. The message "Button was tapped" is printed to the console

D. The button changes color automatically

Solution

1. Step 1: Check action method annotation

   The method showMessage is marked with @objc, so it can be called by the button.

2. Step 2: Understand button tap behavior

   When tapped, the button triggers showMessage, which prints the message.

3. Final Answer:

   The message "Button was tapped" is printed to the console -> Option C

4. Quick Check:

   @objc method called on tap = print message [OK]

Hint: @objc method runs on button tap printing message [OK]

Common Mistakes:

• Forgetting @objc on action method
• Expecting UI changes without code
• Confusing button title with action effect

4. Identify the error in this code snippet that prevents the button action from working:

let button = UIButton()
button.addTarget(self, action: #selector(buttonPressed), for: .touchUpInside)

func buttonPressed() {
    print("Pressed")
}

medium

A. The button title is not set

B. The button is not added to the view

C. The selector syntax is incorrect

D. The action method is missing the @objc attribute

Solution

1. Step 1: Check method declaration for selector

   Methods used with #selector must be marked @objc to be visible to Objective-C runtime.

2. Step 2: Verify other code parts

   While adding button to view and title are important, they don't prevent action from being called.

3. Final Answer:

   The action method is missing the @objc attribute -> Option D

4. Quick Check:

   @objc missing on action method = no call [OK]

Hint: Action methods need @objc to be called by button [OK]

Common Mistakes:

• Ignoring @objc requirement
• Thinking button must have title for action
• Assuming selector syntax is wrong when it's correct

5. You want to create a button that changes its title to "Clicked" when tapped. Which code snippet correctly implements this behavior?

let button = UIButton()
button.setTitle("Tap me", for: .normal)
button.addTarget(self, action: #selector(changeTitle), for: .touchUpInside)

@objc func changeTitle() {
    // What goes here?
}

hard

A. self.button.setTitle("Clicked", for: .normal)

B. button.setTitle("Clicked", for: .normal)

C. button.title = "Clicked"

D. changeTitle.title = "Clicked"

Solution

1. Step 1: Understand scope of button variable

   The button variable is declared outside the method, so inside changeTitle() you must reference it properly, usually as self.button.

2. Step 2: Use correct method to change title

   UIButton's title is changed using setTitle(_:for:) method, not by assigning to a property.

3. Final Answer:

   self.button.setTitle("Clicked", for: .normal) -> Option A

4. Quick Check:

   Use self.button.setTitle to update title [OK]

Hint: Use self.button.setTitle("Clicked", for: .normal) inside action [OK]

Common Mistakes:

• Trying to assign title directly
• Using button without self when needed
• Calling setTitle on wrong object