NEW: Subscribe to Hacking with Swift+ and accelerate your learning! >>

Custom modifiers

Paul Hudson    @twostraws   

SwiftUI gives us a range of built-in modifiers, such as font(), background(), and clipShape(). However, it’s also possible to create custom modifiers that do something specific.

For example, we might say that all titles in our app should have a particular style, so first we need to create a custom ViewModifier struct that does what we want:

struct Title: ViewModifier {
    func body(content: Content) -> some View {
        content
            .font(.largeTitle)
            .foregroundColor(.white)
            .padding()
            .background(Color.blue)
            .clipShape(RoundedRectangle(cornerRadius: 10))
    }
}

We can now use that with the modifier() modifier – yes, it’s a modifier called “modifier”, but it lets us apply any sort of modifier to a view, like this:

Text("Hello World")
    .modifier(Title())

When working with custom modifiers, it’s usually a smart idea to create extensions on View that make them easier to use. For example, we might wrap the Title modifier in an extension such as this:

extension View {
    func titleStyle() -> some View {
        self.modifier(Title())
    }
}

We can now use the modifier like this:

Text("Hello World")
    .titleStyle()

Custom modifiers can do much more than just apply other existing modifiers – they can also create new view structure, as needed. Remember, modifiers return new objects rather than modifying existing ones, so we could create one that embeds the view in a stack and adds another view:

struct Watermark: ViewModifier {
    var text: String

    func body(content: Content) -> some View {
        ZStack(alignment: .bottomTrailing) {
            content
            Text(text)
                .font(.caption)
                .foregroundColor(.white)
                .padding(5)
                .background(Color.black)
        }
    }
}

extension View {
    func watermarked(with text: String) -> some View {
        self.modifier(Watermark(text: text))
    }
}

With that in place, we can now add a watermark to any view like this:

Color.blue
    .frame(width: 300, height: 200)
    .watermarked(with: "Hacking with Swift")
Hacking with Swift is sponsored by NSSpain

SPONSORED Announcing NSSpain 2020: Remote Edition! An online, continuous conference for iOS developers. We’ll start on Thursday and finish on Friday, with talks, activities, and lots of fun for 36 hours, non-stop. Sound good? Join us!

Find out more

Sponsor Hacking with Swift and reach the world's largest Swift community!

BUY OUR BOOKS
Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 4.8/5

Link copied to your pasteboard.