Dynamically sized #State var - swift

Question

I'm loading data into a struct from JSON. With this data, a new structure (itemStructures) is created and filled for use in a SwiftUI View. In this View I have a #State var which I manually initialise to have enough space to hold all items. This state var holds all parameters which are nested within the items, hence the nested array.
As long as this #State var has enough empty spaces everything works fine. But my question is, how do I modify this #State programmatically for when the number of items increases er decreases with the loading of a new JSON? I could make it really large but I'd rather have it the exact size after each load.
//Structs used in this example
struct MainViewState {
var itemStructures: [ItemStructure]
}
struct ItemStructure: Identifiable, Hashable {
var id: String {name}
var name: String
var parameters: [Parameter]
}
struct Parameter: Identifiable, Hashable {
var id: String {name}
var name: String
var value: Double
var range: [Double]
}
struct ContentView: View {
//In this model json is loaded, this seemed out of scope for this question to include this
#ObservedObject var viewModel: MainViewModel
//This is the #State var which should be dynamically allocated according to the content size of "itemStructures"
//For now 3 items with 10 parameters each are enough
#State var parametersPerItem: [[Float]] = [
[0,0,0,0,0,0,0,0,0,0],
[0,0,0,0,0,0,0,0,0,0],
[0,0,0,0,0,0,0,0,0,0]
]
init(viewModel: MainViewModel) {
self.viewModel = viewModel
}
var body: some View {
let itemStructures = viewModel.mainState.itemStructures
ForEach( Array(itemStructures.enumerated()), id: \.element ) { index, item in
Text(item.name)
ForEach( Array(item.parameters.enumerated()), id: \.element ) { i, parameter in
Text(parameter.name)
SliderView(
label: parameter.name,
value: Binding(
get: { self.parametersPerItem[index][i] },
set: { (newVal) in
self.parametersPerItem[index][i] = newVal
//Function to send slider values and ranges to real time processing
//doStuffWithRangesAndValues()
}
),
range: parameter.range,
showsLabel: false
).onAppear {
//Set initial value slider
parametersPerItem[index][i] = Float(parameter.value)
}
}
}
}
}
struct SliderView: View {
var label: String
#Binding var value: Float
var range: [Double]
var showsLabel: Bool
init(label: String, value: Binding<Float>, range: [Double], showsLabel: Bool = true) {
self.label = label
_value = value
self.range = range
self.showsLabel = showsLabel
}
var body: some View {
GeometryReader { geometry in
ZStack{
if showsLabel { Text(label) }
HStack {
Slider(value: $value)
.foregroundColor(.accentColor)
.frame(width: geometry.size.width * 0.8)
//In the real app range calculations are done here
let valueInRange = value
Text("\(valueInRange, specifier: range[1] >= 1000 ? "%.0f" : "%.2f")")
.foregroundColor(.white)
.font(.subheadline)
.frame(width: geometry.size.width * 0.2)
}
}
}
.frame(height: 40.0)
}
}

Answer 1

If you are looking for a solution where you want to initialise the array after the json has been loaded you could add a computed property in an extension to the main/root json model and use it to give the #State property an initial value.
extension MainViewState {
var parametersPerItem: [[Float]] {
var array: [[Float]] = []
if let max = itemStructures.map(\.parameters.count).max(by: { $0 < $1 }) {
for _ in itemStructures {
array.append(Array(repeating: 0.0, count: max))
}
}
return array
}
}