Hi, When using SwiftUI ‘List’ with a large number of elements (4000+), I noticed a significant performance issue if extracting the views inside the ‘ForEach’ block into their own subview class. It affects scrolling performance, and using the scroll handle in the scrollbar causes stutters and beachballs. This seems to happen on macOS only ... the same project works fine on iOS.
Here's an example of what I mean:
List (selection: $multiSelectedContacts) {
ForEach(items) { item in
// 1. this subview is the problem ... replace it with the contents of the subview, and it works fine
PlainContentItemView(item: item)
// 2. Uncomment this part for it to work fine (and comment out PlainContentItemView above)
/*HStack {
if let timestamp = item.timestamp, let itemNumber = item.itemNumber {
Text("\(itemNumber) - \(timestamp, formatter: itemFormatter)")
}
}*/
}
}
struct PlainContentItemView: View {
let item: Item
var body: some View {
HStack {
if let timestamp = item.timestamp, let itemNumber = item.itemNumber {
Text("\(itemNumber) - \(timestamp, formatter: itemFormatter)")
}
}
}
}
Item is a NSManagedObject subclass, and conforms to Identifiable by using the objectID string value.
With this, scrolling up and down using the scrolling handle, causes stuttering scrolling and can beachball on my machine (MacBook Pro M1).
If I comment out the ‘PlainContentItemView’ and just use the HStack directly (which is what was extracted to ‘PlainContentItemView’), the performance noticeably improves, and I can scroll up and down smoothly.
Is this just a bug with SwiftUI, and/or can I do something to improve this?
