Ios swift - Make SwiftUI List view reusable

NNikN
November 23, 2023
285 views
0 votes
2 Answers

The below list view loads 1000 rows and I see 1000 NameTextView being created.

But with reusability we should be seeing very few NameTextView. Is there a way to optimize the code and number of rows that will be created.

I am doing similar thing as posted in Answer for question Reusability support in List in SwiftUI


import SwiftUI

struct ListContentView: View {
    var items = createList()
    var body: some View {
        List(items) { element  in
            NameTextView(name: element.name)
        }
        .listStyle(PlainListStyle())
    }
}

struct NameTextView: View {
    var name: String
    var body: some View {
        Text(name)
    }
}

#Preview {
    ListContentView()
}

struct ListElement: Identifiable {
    var id = UUID().uuidString
    var name: String
}



func createList()  -> [ListElement] {
    var items: [ListElement] = []
    
    for i in 0..<1000 {
        items.append(ListElement(name: "Name (i)"))
        
    }
    return items
}

Answers

- Paulw11
- November 22, 2023 at 11:00 pm
- 0 votes
0
SwiftUI views make use of UIKit components under the covers, but that doesn’t mean that SwiftUI views are just direct wrappers around UIKit components.

In the case of a List you have some SwiftUI view (NameTextView in your case) being shown in a UICollectionViewCell, but there is not a 1:1 correspondence between the number of NameTextViews and the number of underlying cells that are needed.

SwiftUI views are immutable structs and so a unique struct instance is required for each NameTextView – In your case, a total of 10,000 will be required, but only if you scrolled to the end of the list; additional views are created as you scroll and they need to be shown.

These are displayed on a number of UICollectionViewCells – You don’t have direct visibility of the creation or reuse of these cells, but I would expect that there would be about n+4 of them for a list with n visible rows (the extra cells allow for off-screen cells in preparation for scrolling).

So, the short answer is you cannot make SwiftUI views reusable because SwiftUI views are immutable structs. Every time there is any change in a SwiftUI view, a new view is created to replace the old one.

The underlying collection view cells are re-used.

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- MojtabaHosseini
- November 23, 2023 at 9:04 am
- 0 votes
0
❌ It seems like you did an incorrect measurement because

✅ List is reusable in SwiftUI!

Whether its backed by UICollectionView for newer SwiftUI versions or UITableView for older versions (or the AppKit counterparts for the macOS), List always reuses its items (not the parent hosting view itself)

Here is more information (for the SwiftUI 1 but the latest does the same with collection view)

You can see there are only a few (reusable) items.

_{⚠️ The image is cropped to pay attention to the focused area but as you can see, obviously there is not 1000 items.}

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