I'm trying to use the new (announced at WWDC 2023 and available in iOS 17 and macOS 14) API to observe scroll position of SwiftUI ScrollView.
I have the following view, but I can't make it work correctly. That is, using the scrollPosition(id:anchor) view modifier makes the scroll view go nuts. At some point, and in some cases even at the very beginning, the scroll view just starts jumping and is stuttering when trying to scroll. See the screen recording here: https://mastodon.social/@tomkraina/111249340792812592
The code:
struct ContentView: View {
private var itemSize: CGSize = .init(width: 50.0, height: 50.0)
// Annotated as @State to create the sections only once
@State private var sectionData = makeSections()
// Tracking scroll position
@State private var currentItemID: MyIdentifier?
var currentItemDescription: String { self.currentItemID?.stringId ?? "nil" }
var body: some View {
VStack {
// 1. Scroll View
ScrollView(.vertical) {
LazyVGrid(
columns: [.init(.adaptive(minimum: self.itemSize.width), spacing: Constants.columnSpacing, alignment: .center)],
alignment: .center,
spacing: Constants.sectionSpacing
) {
ForEach(self.sectionData) { section in
Section(section.title) {
ForEach(section.items) { item in
Text(item.text)
.frame(width: self.itemSize.width, height: self.itemSize.height)
}
}
}
}
.scrollTargetLayout()
}
.scrollPosition(id: self.$currentItemID) // TODO: Comment out this line to make the scrolling work
Divider()
// 2. Settings
Group {
Label(
title: { Text(self.currentItemDescription) },
icon: { Image(systemName: "42.circle") }
)
}
.padding()
}
#if os(macOS)
.frame(width: 320, height: 480, alignment: .center)
#endif
}
}
The whole code can be found in my GitHub repo: https://github.com/tomaskraina/feedbackassistant.apple.com/blob/master/ScrollPositionVsLazyVGrid/ScrollPositionVsLazyVGrid/ContentView.swift
Am I doing something wrong or is this a bug in SwiftUI?
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