Question 68264 in IOS Swift Question posted in
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Is there a way to detect only the cells displayed on the screen when using List in SwiftUI? – Ios swift

Is it possible to detect the cell (or array position) of the List currently displayed on the View screen from among the 100 Items as shown below?

Also, at that time, I would like to get the position of the cell in detail, such as some cells that are half hidden from the screen at the top and bottom.

struct DemoList: View {
    // 1.
    @State private var items: [Item] = (0..<100).map { Item(title: "Item #($0)") }

    // 2.
    var body: some View {
        List {
            ForEach(items) { item in
                Text(item.title)
            }
        }
    }
}
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2

Answers


  1. 0

    Try using ‘onAppear’ modifier as Text(text).onAppear {}
    Since iOS 15 there have been improvements around that modifier

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  2. 0

    This might be a starting point. But beware that List always keeps one "buffer" cell before .onAppear/.onDisappear kick in.

            List {
            ForEach(items) { item in
                GeometryReader { geo in
                    Text(item.title)
                        .onAppear {
                            print(item.title, geo.frame(in: .global))
                        }
                        .onDisappear {
                            print(item.title, "---")
                        }
                }
            }
        }

    A more sophisticated approach would use PreferenceKey. I recommend this (look for "GridInfoPreference"): https://swiftui-lab.com/impossible-grids/

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