Reverse binding to parent view model from child view model - ios

Question

I have a main view model called CustomizeMenuItemViewModel which has a property maxItemCount which needs to be decreased to 0 whenever the user interacts with the view to add one item in the shopping bag. The view interacts with its own view model called CustomizationQuantityCellViewModel which is instantiated from the main view model.
I cannot find a way to bind the property maxItemCount to the view interaction which has CustomizationQuantityCellViewModel in between.
Relevant Code:
final class CustomizeMenuItemViewModel {
private(set) var item: MenuItem
#Binding private(set) var maxUnitCount: Int
// MARK: - Initializer
init(item: MenuItem) {
self.item = item
_maxUnitCount = .constant(0)
}
func menuItem(option: Option, index: Int) -> MenuItemCellType {
let selections = Array(option.selections)
if option.multiselect {
if option.max > 0 {
maxUnitCount = option.max
return .quantity(CustomizationQuantityCellViewModel(selection: selections[index], maxUnit: $maxUnitCount), (index != selections.count - 1))
} else {
return .checkbox(CustomizationMenuItemCellViewModel(selection: selections[index]), (index != selections.count - 1))
}
} else {
if option.name.lowercased().contains("bun") {
return .card(CustomizationMenuItemCellViewModel(selection: selections[index]), (index != selections.count - 1))
} else if option.max > 0 {
maxUnitCount = option.max
return .quantity(CustomizationQuantityCellViewModel(selection: selections[index], maxUnit: $maxUnitCount), (index != selections.count - 1))
} else {
return .radiobutton(CustomizationMenuItemCellViewModel(selection: selections[index]), (index != selections.count - 1))
}
}
}
}
final class CustomizationQuantityCellViewModel: ObservableObject {
// MARK: - Properties
private(set) var selection: Selection
#Binding private(set) var maxUnit: Int
#Published private(set) var selectedUnits: Int
// MARK: - Initializer
init(selection: Selection, maxUnit: Binding<Int>) {
self.selection = selection
self._maxUnit = maxUnit
self.selectedUnits = 0
}
func increaseSelectedUnit() {
if maxUnit > 0 {
selectedUnits += 1
maxUnit -= 1
}
}
func decreseSelectedUnit() {
if selectedUnits > 0 {
selectedUnits -= 1
maxUnit += 1
}
}
}
struct CustomizationQuantityCell: View {
// MARK: - Properties
#ObservedObject private var viewModel: CustomizationQuantityCellViewModel
// MARK: - Initializer
init(viewModel: CustomizationQuantityCellViewModel) {
self.viewModel = viewModel
}
// MARK: - Body
var body: some View {
VStack {
HStack(spacing: 16) {
Text(viewModel.selection.name)
.font(.system(size: 16))
.foregroundColor(Color(Colors.brown500.color))
.padding(.top, 20)
.padding(.bottom, 20)
Spacer()
HStack(spacing: 32) {
Button {
viewModel.decreseSelectedUnit()
} label: {
Image(Images.minus.name)
}
.buttonStyle(.plain)
Text("\(viewModel.selectedUnits)")
.font(.system(size: 15))
.foregroundColor(Color(Colors.brown500.color))
Button {
viewModel.increaseSelectedUnit()
} label: {
Image(Images.plus.name)
}
.buttonStyle(.plain)
}
}
}
}
}
I tried the above approach but the binding always set 0 to maxUnitCount.

Answer 1

Just remove your binding from your maxUnitcount and make that view model ObservableObject.
final class CustomizeMenuItemViewModel: ObservableObject {
private(set) var item: MenuItem
#Published private(set) var maxUnitCount: Int
And the other thing you need to change is your the other viewmodel. It will work.
final class CustomizationQuantityCellViewModel: ObservableObject {
// MARK: - Properties
private(set) var selection: Selection
private(set) var maxUnit: Int
private(set) var selectedUnits: Int
// MARK: - Initializer
init(selection: Selection, maxUnit: Int) {
self.selection = selection
self._maxUnit = maxUnit
self.selectedUnits = 0
}
}