SwiftUI: How to know change in the published var of an ObservableObject - ios

Question

I have a View which shows list of Toggle's based on the Model data. This model has a #Published variable which changes based toggle selection.
class Model: ObservableObject, Hashable {
var id: String
#Published var isSelected: Bool
init(id: String, isSelected: Bool) {
self.id = id
self.isSelected = isSelected
}
...
}
class ViewModel: ObservableObject {
var list: [Model]
init() { ...}
...
func save() {
}
func clear() {
}
}
struct MyView: View {
#ObservedObject var viewModel: ViewModel
var body: some View {
VStack {
ForEach(viewModel.list, id: \.self) { model in
Toggle(model.id, isOn: $model.isSelected)
}
Button("Done") {
viewModel.save()
}
Button("Clear") {
viewModel.clear()
}
...
}
}
}
The question is, since I have array of models with #Publsihed,
How to know if the user has changed any of the Toggles or not, so I can enable/disable Save button
How to know list all toggles that are changed(i.e. models isSelected is changed), say like when I press save

Answer 1

try something like this approach, to change the list of models isSelected property.
struct Model: Identifiable, Hashable {
var id: String
var isSelected: Bool
var hasChanged: Bool = false // <--- here
}
class ViewModel: ObservableObject {
// for testing
#Published var list: [Model] = [Model(id: "1", isSelected: false),
Model(id: "2", isSelected: false),
Model(id: "3", isSelected: true)]
func save() {
for mdl in list {
if mdl.hasChanged {
print("---> \(mdl.id) has changed") // <-- here
}
}
}
func clear() {
list = []
print("---> clear list: \(list)")
}
func reset() {
for i in list.indices {
list[i].isSelected = false
}
print("---> reset list: \(list)")
}
}
struct ContentView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
MyView(viewModel: viewModel)
}
}
struct MyView: View {
#ObservedObject var viewModel: ViewModel
#State var hasChanged = false
var body: some View {
VStack {
ForEach($viewModel.list) { $model in
Toggle(model.id, isOn: $model.isSelected)
.onChange(of: model.isSelected) { val in // <-- here
model.hasChanged.toggle()
}
}
Button("Save") {
viewModel.save()
}
Button("Clear") {
viewModel.clear()
}
Button("Reset") {
viewModel.reset()
}
}
}
}
EDIT-1:
If you want to count the number of times a particular Model has changed, then
simply add a counter to it, such as in this example code:
struct MyView: View {
#ObservedObject var viewModel: ViewModel
var body: some View {
VStack {
ForEach($viewModel.list) { $model in
Toggle(model.id, isOn: $model.isSelected)
.onChange(of: model.isSelected) { val in
model.changeCount += 1 // <-- here
}
}
Button("Save") {
viewModel.save()
}
Button("Clear") {
viewModel.clear()
}
Button("Reset") {
viewModel.reset()
}
}
}
}
struct Model: Identifiable, Hashable {
var id: String
var isSelected: Bool
var changeCount: Int = 0 // <--- here
}
class ViewModel: ObservableObject {
// for testing
#Published var list: [Model] = [Model(id: "1", isSelected: false),
Model(id: "2", isSelected: false),
Model(id: "3", isSelected: true)]
func save() {
for var mdl in list {
print("---> \(mdl.id) has changed \(mdl.changeCount) times") // <-- here
}
}
func clear() {
list = []
print("---> clear list: \(list)")
}
func reset() {
for i in list.indices {
list[i].isSelected = false
}
print("---> reset list: \(list)")
}
}