Custom ViewModifiers in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a simple custom ViewModifier named RedTitle that makes text red and bold.

iOS Swift

struct RedTitle: ViewModifier {
  func body(content: Content) -> some View {
    content
      .foregroundColor([1])
      .bold()
  }
}

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

AUIColor.red

B.red

CColor.red

Dred

Attempts:

3 left

💡 Hint

Common Mistakes

Using UIColor instead of Color for SwiftUI colors.

Trying to use .red without Color prefix.

The correct way to set the text color in SwiftUI is using Color.red, not .red or UIColor.red.

2fill in blank

medium

Complete the code to apply the custom ViewModifier RedTitle to a Text view.

iOS Swift

Text("Hello World")
  .[1](RedTitle())

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

Amodifier

Bstyle

Cuse

Dapply

Attempts:

3 left

💡 Hint

Common Mistakes

Using .apply or .use which do not exist in SwiftUI.

Trying to call the modifier without parentheses.

The correct method to apply a custom ViewModifier is .modifier().

3fill in blank

hard

Fix the error in the custom ViewModifier by completing the missing return type for the body function.

iOS Swift

struct BlueBackground: ViewModifier {
  func body(content: Content) -> [1] {
    content
      .background(Color.blue)
  }
}

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

Asome View

BView

CVoid

DContent

Attempts:

3 left

💡 Hint

Common Mistakes

Returning Void or Content instead of some View.

Omitting the return type.

The body function must return some View to conform to ViewModifier protocol.

4fill in blank

hard

Fill both blanks to create a reusable ViewModifier named RoundedBorder that adds a rounded border with a given color and width.

iOS Swift

struct RoundedBorder: ViewModifier {
  var color: Color
  var width: CGFloat

  func body(content: Content) -> some View {
    content
      .overlay(
        RoundedRectangle(cornerRadius: [1])
          .stroke(color, lineWidth: [2])
      )
  }
}

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

A10

B5

C15

D20

Attempts:

3 left

💡 Hint

Common Mistakes

Using very large corner radius or line width values.

Mixing up corner radius and line width values.

A corner radius of 10 and line width of 5 create a nicely rounded border.

5fill in blank

hard

Fill all three blanks to create a View extension that applies the RoundedBorder modifier with default color and width.

iOS Swift

extension View {
  func roundedBorder() -> some View {
    self.modifier(RoundedBorder(color: [1], width: [2]))
  }

  func roundedBorder(color: Color, width: CGFloat) -> some View {
    self.modifier(RoundedBorder(color: color, width: [3]))
  }
}

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

AColor.gray

B3

Cwidth

DColor.black

Attempts:

3 left

💡 Hint

Common Mistakes

Using a literal number instead of the parameter in the second method.

Mixing up default color values.

The default color is Color.black, default width is 3, and the second method uses the passed width parameter.

Practice

1. What is the main purpose of creating a custom ViewModifier in SwiftUI?

easy

A. To reuse a set of view styles and behaviors easily

B. To create a new type of view from scratch

C. To handle user input events directly

D. To manage app navigation between screens

Solution

1. Step 1: Understand what a ViewModifier does

   A ViewModifier bundles styling and behavior changes for views.

2. Step 2: Identify the main use

   It helps reuse these styles easily across many views.

3. Final Answer:

   To reuse a set of view styles and behaviors easily -> Option A

4. Quick Check:

   Custom ViewModifiers = reuse styles [OK]

Hint: Think: reuse styles and behaviors with one modifier [OK]

Common Mistakes:

• Confusing ViewModifier with creating new views
• Thinking it handles navigation or input directly
• Assuming it manages app state

2. Which of the following is the correct way to apply a custom ViewModifier named Highlight to a Text view?

easy

A. Text("Hello").modifier(Highlight())

B. Text("Hello").applyModifier(Highlight)

C. Text("Hello").useModifier(Highlight())

D. Text("Hello").addModifier(Highlight)

Solution

1. Step 1: Recall the correct method name

   The method to apply a ViewModifier is .modifier().

2. Step 2: Check syntax for applying Highlight

   It should be .modifier(Highlight()) with parentheses to create the modifier instance.

3. Final Answer:

   Text("Hello").modifier(Highlight()) -> Option A

4. Quick Check:

   Use .modifier() with instance [OK]

Hint: Remember: .modifier() takes an instance with () [OK]

Common Mistakes:

• Using wrong method names like applyModifier or addModifier
• Forgetting parentheses after modifier name
• Passing type instead of instance

3. Given this custom ViewModifier:

struct RedTitle: ViewModifier {
  func body(content: Content) -> some View {
    content
      .font(.title)
      .foregroundColor(.red)
  }
}

What will this code display?

Text("Welcome").modifier(RedTitle())

medium

A. Text "Welcome" with no changes

B. Text "Welcome" in default color with title font

C. Text "Welcome" in red color with default font

D. Text "Welcome" in red color with title font

Solution

1. Step 1: Analyze the RedTitle modifier

   It sets the font to title and text color to red.

2. Step 2: Apply modifier to Text("Welcome")

   The text will appear with title font size and red color.

3. Final Answer:

   Text "Welcome" in red color with title font -> Option D

4. Quick Check:

   RedTitle = red + title font [OK]

Hint: Look at modifier body: font and color changes [OK]

Common Mistakes:

• Ignoring the font change
• Assuming default color remains
• Confusing modifier effects

4. What is wrong with this custom ViewModifier code?

struct BlueBackground: ViewModifier {
  func body(content: Content) -> some View {
    content.background(Color.blue)
  }

  func body(content: Content) -> some View {
    content.padding()
  }
}

medium

A. Background modifier is not allowed inside ViewModifier

B. Two body functions cause a duplicate method error

C. Missing return keyword in body functions

D. Padding modifier must be applied before background

Solution

1. Step 1: Check method definitions in struct

   There are two body(content:) methods defined, which is not allowed.

2. Step 2: Understand Swift rules for method overloading

   Swift does not allow two methods with the same signature in one struct.

3. Final Answer:

   Two body functions cause a duplicate method error -> Option B

4. Quick Check:

   Duplicate body() methods = error [OK]

Hint: Only one body(content:) allowed per ViewModifier [OK]

Common Mistakes:

• Trying to overload body method
• Forgetting return keyword (not needed here)
• Misunderstanding modifier order rules

5. You want to create a custom ViewModifier that adds a rounded border only if a Boolean highlight is true. Which of these implementations correctly applies the border conditionally?

hard

A. struct ConditionalBorder: ViewModifier {
var highlight: Bool
func body(content: Content) -> some View {
if highlight {
content.border(Color.green, width: 2)
} else {
content
}
}
}

B. struct ConditionalBorder: ViewModifier {
var highlight: Bool
func body(content: Content) -> some View {
content.border(highlight ? Color.green : Color.clear, width: 2)
}
}

C. struct ConditionalBorder: ViewModifier {
var highlight: Bool
func body(content: Content) -> some View {
content
.border(Color.green, width: highlight ? 2 : 0)
}
}

D. struct ConditionalBorder: ViewModifier {
var highlight: Bool
func body(content: Content) -> some View {
content
.border(Color.green, width: highlight)
}
}

Solution

1. Step 1: Eliminate compile errors

   struct ConditionalBorder: ViewModifier { var highlight: Bool func body(content: Content) -> some View { if highlight { content.border(Color.green, width: 2) } else { content } } } returns different view types in if-else (compiler error). struct ConditionalBorder: ViewModifier { var highlight: Bool func body(content: Content) -> some View { content .border(Color.green, width: highlight) } } passes Bool to width (CGFloat expected, type error).

2. Step 2: Compare remaining options

   struct ConditionalBorder: ViewModifier { var highlight: Bool func body(content: Content) -> some View { content.border(highlight ? Color.green : Color.clear, width: 2) } } uses Color.clear with fixed width 2: invisible but expands frame (layout shift). struct ConditionalBorder: ViewModifier { var highlight: Bool func body(content: Content) -> some View { content .border(Color.green, width: highlight ? 2 : 0) } } uses conditional width 2/0: border only when true, no layout shift.

3. Final Answer:

   content.border(Color.green, width: highlight ? 2 : 0) -> Option C

4. Quick Check:

   Conditional width = correct conditional border [OK]

Hint: Ternary on width for conditional border without layout shift [OK]

Common Mistakes:

• Returning different view types in if-else inside body
• Passing Bool where CGFloat is expected
• Using Color.clear with fixed width (layout shift)