iOS ScrollView and make it snappy!

In iOS17, Swift UI has some new modifiers which make it easier to implement snap behaviour in scrollviews.

ScrollView

Let’s make a simple scrollview:

import SwiftUI

struct ContentView: View {
    var body: some View {
        ScrollView(.horizontal) {
            LazyHStack {
                ForEach(0..<20) { i in
                    TileView(title: String(i))
                }
            }
            .padding()
        }
    }}

struct TileView: View {
    let title: String
    var body: some View {
        Text(title)
            .foregroundStyle(.white)
            .frame(width: 150, height: 100)
            .background(.purple)
            .clipShape(.rect(cornerRadius: 20))
    }
}

#Preview {
    ContentView()
}

Reminder: Using LazyHStack instead of HStack means the tiles are only loaded when needed and not upfront.

This gives us a simple horizontal scrollview:

The default behaviour is free scrolling, and the view stays wherever it finishes after scrolling:

Paging Behaviour

We can add the modifier .scrollTargetBehavior(.paging) to our scrollview:

struct ContentView: View {
    var body: some View {
        ScrollView(.horizontal) {
            LazyHStack {
                ForEach(0..<20) { i in
                    TileView(title: String(i))
                }
            }
            .padding()
        }
        .scrollTargetBehavior(.paging)
    }
}

This means the scrollview will scroll one screen width at a time and snaps nicely to each page:

View Aligned Behaviour

Instead of using paging, we can use the modifier .scrollTargetBehavior(.viewAligned) along with .scrollTargetLayout() on the view we want to be used for settling.

struct ContentView: View {
    var body: some View {
        ScrollView(.horizontal) {
            LazyHStack {
                ForEach(0..<20) { i in
                    TileView(title: String(i))
                }
            }
            .padding()
            .scrollTargetLayout()
        }
        .scrollTargetBehavior(.viewAligned)
    }
}

This gives us the the following behaviour where the scrollview snaps to the individual views:

Additional Notes

This can all be applied to vertical scrollviews as well. I’ve just used horizontal ones here as examples.

These modifiers are only available in iOS 17 / Xcode 15.

More information and options to experiment with in Apple’s docs https://developer.apple.com/documentation/swiftui/scrolltargetbehavior