The problem of @State optional objects not being released in a LazyVStack

Question

Created Oct ’23

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I have a LazyVStack wrapped in a ScrollView, and within the LazyVStack, there is a group of SomeThingView used to display certain things.

import SwiftUI

var appearCount = 0

class MyObject {
    static var count = 0
    init(){
        MyObject.count += 1
    }
    deinit {
        MyObject.count -= 1
        print("deinit ImageCount: \(MyObject.count)")
    }
}

struct SomeThingView: View {
    @State var object: MyObject? = nil
    @State var show: Bool = false

    var body: some View {
        ZStack {
            if show {      // <- The issue lies here, with this condition, the image will never be released.
                Text("load")
            } else {
                Text("not load")
            }
        }
        .frame(height: 100)
        .onAppear {
            show = true
            
            object = MyObject()
                        
            appearCount += 1
            print("appear \(appearCount)")
        }
        .onDisappear {
            show = false
            
            object = nil             // <- Unreferencing the image here, the image should be released.
            
            appearCount -= 1
            print("disappear \(appearCount)")
            print("disappear ImageCount: \(MyObject.count)")
        }
    }
}

struct ContentView: View {
    var body: some View {
        VStack {
            ScrollView{
                LazyVStack{
                    ForEach(0..<100) {_ in
                        SomeThingView()
                    }
                }
            }
           
        }
        .padding()
    }
}

The current issue lies in the fact that the @State var object: MyObject? = nil within SomeThingView is not being released due to the presence of @State var show: Bool = false. As seen above, i set show = true and object = MyObject() in the onAppear block, and in onDisappear, set show = false and object = nil. Even though i am not using object in the view, the presence of the show condition within the ZStack{} is preventing the object from being released properly. some log

disappear 7
disappear ImageCount: 57
init ImageCount: 58
appear 8
disappear 7
disappear ImageCount: 58
init ImageCount: 59
appear 8
disappear 7
disappear ImageCount: 59
init ImageCount: 60
appear 8
disappear 7
disappear ImageCount: 60
init ImageCount: 61
appear 8

However, if I comment out the condition for show within the ZStack, or if I comment out the settings for show in onAppear and onDisappear, everything runs smoothly.

struct SomeThingView: View {
    @State var object: MyObject? = nil
    @State var show: Bool = false

    var body: some View {
        ZStack {
//            if show {      // <- The issue lies here, with this condition, the image will never be released.
//                Text("load")
//            } else {
//                Text("not load")
//            }
        }
        .frame(height: 100)
        .onAppear {
            show = true
            
            object = MyObject()
                        
            appearCount += 1
            print("appear \(appearCount)")
        }
        .onDisappear {
            show = false
            
            object = nil             // <- Unreferencing the image here, the image should be released.
            
            appearCount -= 1
            print("disappear \(appearCount)")
            print("disappear ImageCount: \(MyObject.count)")
        }
    }
}

deinit ImageCount: 9
deinit ImageCount: 8
disappear 7
disappear ImageCount: 8
init ImageCount: 9
appear 8
deinit ImageCount: 8
disappear 7
disappear ImageCount: 8
init ImageCount: 9
appear 8
deinit ImageCount: 8
disappear 7
disappear ImageCount: 8
init ImageCount: 9
appear 8
deinit ImageCount: 8
init ImageCount: 9
appear 9
disappear 8
disappear ImageCount: 9
init ImageCount: 10
appear 9
deinit ImageCount: 9
disappear 8
disappear ImageCount: 9
init ImageCount: 10
appear 9
deinit ImageCount: 9

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