SwiftUI ScrollViewReader tutorial
In SwiftUI a ScrollViewReader is a view that provides programmatic scrolling inside sub views. With the scrollTo method the scrolling is executed. In his tutorial an item number can be chosen using a stepper. When the number is selected the ScrollViewReader will scroll to the chosen item. This tutorial is built for iOS 14 and Xcode 12, which can be download at the Apple developer portal.
Open Xcode and either click Create a new Xcode project in Xcode’s startup window, or choose File > New > Project. In the template selector, select iOS as the platform, select App template in the Application section and then click Next.
Enter SwiftUIScrollViewReaderTutorial as the Product Name, select SwiftUI as Interface, SwiftUI App as Life Cycle and Swift as Language. Deselect the Include Tests checkbos and click Next. Choose a location to save the project on your Mac.
In the canvas, click Resume to display the preview. If the canvas isn’t visible, select Editor > Editor and Canvas to show it.
In the Project navigator, click to select ContentView.swift. Change the code inside the ContentView struct to
struct ContentView: View { // 1. let colors: [Color] = [.yellow, .red, .blue] @State private var itemNumber = 1 var body: some View { ScrollView { // 2. ScrollViewReader { value in HStack { // 3. Stepper(value: $itemNumber, label: { Text("Jump to Item: ") }) Button { withAnimation { // 4. value.scrollTo(itemNumber) } } label: { Text("\(itemNumber)") } }.padding() // 5. ForEach(1..<10) { i in Text("Item \(i)") .frame(width: 300, height: 200) .background(colors[i % colors.count]) .id(i) } } } } }
The property constant colors is use as background of the displayed items. The state variable will hold the current item number where will be scrolled to
The ScrollviewReader is used to provide access to the scrollTo method and the subview where will be scrolled to.
A stepper is displayed with the current value of the itemNumber which can be in- and decremented
The scrollTo(_:) method scrolls to the current view which matches the id of the view in the ForEach loop
The ForEach loop generates ten items with colored boxes, each item is assigned an id.
Go to the Preview and choose live preview. Change the number inside the stepper and click the number to scoll the selected colored item.
The source code of the SwiftUIScrollViewReaderTutorial can be downloaded at the ioscreator repository on Github.
