How to change #Published var affects another #Published var like Binding - swift

Question

Is there a way to make #Published var in a way that changes it will affect another #Published var like a Binding var?
import SwiftUI
struct ContentView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
ForEach(viewModel.items, id: \.self){ item in
Button("Select \(item.title)"){
viewModel.selectedItem = item
viewModel.selectedItem.title = "grape"
print(viewModel.items) // <-- This will print [Test.Item(title: "Apple"), Test.Item(title: "Banana"), Test.Item(title: "Orange")]
}
}
}
}
struct Item: Hashable {
var title: String
}
class ViewModel: ObservableObject {
#Published var items: [Item] = [Item(title: "Apple"), Item(title: "Banana"), Item(title: "Orange")]
#Published var selectedItem: Item = Item(title: "default") //<-- I want this to be a binding of an item in the bucket above, so what I modify to selectedItem will affect item in the bucket.
}

Answer 1

Three possible solutions -- the last one might be closest to what you're asking for in terms of one #Published reacting to another.
Here's a version using didSet:
struct ContentView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
ForEach(viewModel.items, id: \.self){ item in
Button("Select \(item.title)"){
viewModel.selectedItem = item
viewModel.selectedItem?.title = "grape"
print(viewModel.items)
}
}
}
}
struct Item: Hashable {
var id = UUID()
var title: String
}
class ViewModel: ObservableObject {
#Published var selectedItem : Item? {
didSet { //when there's a new value, see if it should be mapped into the original item set
self.items = self.items.map {
if let selectedItem = selectedItem, selectedItem.id == $0.id {
return selectedItem
}
return $0
}
}
}
#Published var items: [Item] = [Item(title: "Apple"), Item(title: "Banana"), Item(title: "Orange")]
}
Here's one possibility, using a custom Binding:
struct ContentView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
ForEach(viewModel.items, id: \.self){ item in
Button("Select \(item.title)"){
viewModel.selectedItemID = item.id
viewModel.selectedItem?.wrappedValue.title = "grape"
print(viewModel.items)
}
}
}
}
struct Item: Hashable {
var id = UUID()
var title: String
}
class ViewModel: ObservableObject {
#Published var selectedItemID : UUID?
#Published var items: [Item] = [Item(title: "Apple"), Item(title: "Banana"), Item(title: "Orange")]
var selectedItem : Binding<Item>? {
guard let selectedItemID = selectedItemID else {
return nil
}
return .init { () -> Item in
self.items.first(where: {$0.id == selectedItemID}) ?? Item(title: "")
} set: { (item) in
self.items = self.items.map {
if $0.id == selectedItemID { return item }
return $0
}
}
}
}
And, lastly, a version using Combine:
import SwiftUI
import Combine
struct ContentView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
ForEach(viewModel.items, id: \.self){ item in
Button("Select \(item.title)"){
viewModel.selectedItem = item
viewModel.selectedItem?.title = "grape"
print(viewModel.items)
}
}
}
}
struct Item: Hashable {
var id = UUID()
var title: String
}
class ViewModel: ObservableObject {
#Published var selectedItem : Item?
#Published var items: [Item] = [Item(title: "Apple"), Item(title: "Banana"), Item(title: "Orange")]
private var cancellable : AnyCancellable?
init() {
cancellable = $selectedItem
.compactMap { $0 } //remove nil values
.sink(receiveValue: { (newValue) in
self.items = self.items.map {
newValue.id == $0.id ? newValue : $0 //if the ids match, return the new value -- if not, return the old one
}
})
}
}
All three have the same functionality -- it really just depends on what style of coding you prefer. I might personally go for the last option, as Combine and SwiftUI tend to work really well together. It's also easy to extend with filtering, etc.