SwiftUI List updating slowly

user_14848415 0
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I have a SwiftUI List, which has thousands of items. Each item is as such:

class Item: Codable, Identifiable {
    var id = UUID()
    var prop1 = ""
    var prop2 = ""
}

Now I do this:

List(store.items.indices, id: \.self) { index in
    DetailView(item: self.$store.items[index])
}.id(UUID())

I iterate the indicies because I have to pass a Binding to the DetailView.

Now the DetailView has TextFields attached to the Item's properties.

When DetailView changes an Item's properties, it causes the List to refresh ALL of the items, which I dont want.

Also, it's still important that when one of those properties changes, the main view is updated, because on macOS, the main view is still visible even when you click on one of the items.

My question is how to make it so that whenever an Item passed in from the List changes, only update that row?

I also tried a solution mentioned where I use a LazyVStack, and it fixes the performance issue, but I use the List inside of a NavigationView, and the LazyVStack doesn't seem to support that.

Any suggestions are greatly appreciated.

swiftui swift
2 Answers

Remove .id(UUID()) from the List.

By default, List diffs changes and only updates the affected rows. For very large data sets, that .id(UUID()) trick is used to force the whole List to reload when something changes, which may be faster than trying to diff the large dataset. It doesn’t sound like you need it, so it’s actually worse to include it unnecessarily.

Edit: I don’t think binding to the array by index is the problem, but it is unusual and may bite you eventually.

user_16018490

You could use a LazyVStack in a ScrollView as long as you don't need List specific functionality. Lists aren't as efficient as LazyVStacks yet (Apple bug).

ScrollView {
    LazyVStack {
        ForEach(store.items.indices) { index in
            DetailView(item: self.$store.items[index])
        }
    }
}
user_49958280
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