Modifying a value within a struct inside of a @State Array in SwiftUI [closed]

The whole point of using a @State is so that the UI reacts to changes.

Here's something a little more complete, but yet simple enough, to show how you can read and update values and the UI, given your setup.

Note the use of ForEach with a bindings to $items, which gives you a $item binding to work with.

This allows for direct update of the array structs without needing to hit a button to run a function.

The example also includes another method, where you select a specific ID from a list, then use it to locate the item in the array and update its value.

import SwiftUI

struct StateArrayItem: Hashable, Codable, Identifiable {
    let id: Int 
    var value: Int
}

struct StateArrayContentView: View {
    
    //State values
    @State private var selectedItem: StateArrayItem?
    @State private var pickerFieldValue: Int?
    @FocusState private var focusedField: StateArrayItem? // Focus state for each text field
    
    //Sample array
    @State private var items: [StateArrayItem] = [
        StateArrayItem(id: 0, value: 40),
        StateArrayItem(id: 1, value: 68),
        StateArrayItem(id: 2, value: 52),
        StateArrayItem(id: 3, value: 48),
        StateArrayItem(id: 4, value: 33),
        StateArrayItem(id: 5, value: 71),
        StateArrayItem(id: 6, value: 69),
        StateArrayItem(id: 7, value: 22),
        StateArrayItem(id: 8, value: 28),
        StateArrayItem(id: 9, value: 85)
    ]
    
    //Body
    var body: some View {
        
        Form {
            
            //Section
            Section("Change a value and hit Return or tap away"){
                
                //Array items binding loop
                ForEach($items){ $item in
                    HStack {
                        
                        //Actual value for current ID
                        Text("ID: \($item.id) - Value: \(item.value)")
                            .foregroundStyle(item == selectedItem ? .blue : .primary)
                        
                        Spacer()
                        
                        //Given the $item binding, the value will update as soon as a value is entered
                        TextField("ID: \($item.id) - Value is: \($item.value)", value: $item.value, format: .number)
                            .foregroundStyle(item == selectedItem ? .blue : .primary)
                            .multilineTextAlignment(.trailing)
                            .frame(width: 80)
                            .textFieldStyle(.roundedBorder)
                            .focused($focusedField, equals: item)
                            .onChange(of: focusedField) { oldValue, newValue in
                                selectedItem =  newValue != nil ? newValue : selectedItem
                            }
                            .onSubmit {
                                selectedItem = item
                            }
                    }
                    .frame(maxWidth: .infinity, alignment: .center)
                }
            }
            
            //Section
            Section("Update by ID"){
                HStack {
                    Picker("Pick an ID:", selection: $selectedItem){
                        Text("--").tag(nil as StateArrayItem?) // Tag for the placeholder
                        ForEach($items){ $item in
                                Text("\($item.id)").tag(item)
                        }
                    }
                    .tint(.blue)
                    .fixedSize()
                }
                    
                //Show input form and button if an id is selected in the picker (or another textfield focused)
                if let item = selectedItem {
                    HStack(spacing: 10) {
                        TextField("Enter new value", value: $pickerFieldValue, format: .number)
                            .textFieldStyle(.roundedBorder)
                            .focused($focusedField, equals: item)
                            .onSubmit{
                                if let value = pickerFieldValue {
                                    updateValue(of: item, value: value)
                                }
                            }
                            .foregroundStyle(pickerFieldValue == nil ? .blue : pickerFieldValue != nil && item.value != pickerFieldValue ? .red : .green)
                        
                        Spacer()
                        
                        //Actual value for ID selected in the picker
                        Text("ID: \(item.id) Value: \(item.value)")
                    }
                    
                    //Update button
                    Button("Update", action: {
                        //Guard condition for running the update function
                        guard let value = pickerFieldValue else {
                            print("No value to update with...")
                            return
                        }
                        updateValue(of: item, value: value)
                    })
                    .buttonStyle(.borderedProminent)
                    .disabled((pickerFieldValue == nil))
                }
            }
        }
    }
    
    //Function to update an item with a new value
    func updateValue(of item: StateArrayItem, value: Int) {
        
        //Find the item in the array, based on its index - since item itself is a let constant
        guard let index = items.firstIndex(of: item) else { return }
        
        //Update the value
        items[index].value = value
        
        //Update the selectedItem with the newly modified item
        selectedItem = items[index]
    }
}

#Preview {
    StateArrayContentView()
}