onReceive not getting called in SwiftUI View when ObservedObject changes - ios

Question

I don't manage to trigger the onReceive method in a SwiftUI View whenever a variable from ObservedObject changes.
I tried two methods: using #Publish and using PassthroughSubject<>
Here is the ViewModel
class MenuViewModel: ObservableObject {
#Published var selectedItems = Set<UUID>()
#Published var currentFocusItem: UUID?
// Output
let newItemOnFocus = PassthroughSubject<(UUID?), Never>()
// This function gets called good :)
func tapOnMenuItem(_ item: MenuItem) {
if selectedItems.contains(item.id) {
//These changes should trigger the onReceive?
currentFocusItem = item.id
newItemOnFocus.send(item.id)
} else {
selectedItems.insert(item.id)
currentFocusItem = nil
newItemOnFocus.send(nil)
}
}
}
Here is the View when trying to catch the changes in #Published var currentFocusItem
struct MenuView: View {
#ObservedObject private var viewModel: MenuViewModel
#State var showPicker = false
#State private var menu: Menu = Menu.mockMenu()
init(viewModel: MenuViewModel = MenuViewModel()) {
self.viewModel = viewModel
}
var body: some View {
VStack {
List(menu.items, selection: $viewModel.selectedItems) { item in
MenuItemView(item: item)
}
Divider()
getBottomView(showPicker: showPicker)
}
.navigationBarTitle("Title")
.navigationBarItems(trailing: Button(action: closeModal) {
Image(systemName: "xmark")
})
.onReceive(viewModel.$currentFocusItem, perform: { itemUUID in
self.showPicker = itemUUID != nil // <-- This only gets called at launch time
})
}
}
The View in the same way but trying to catch the PassthroughSubject<>
.onReceive(viewModel.newItemOnFocus, perform: { itemUUID in
self.showPicker = itemUUID != nil // <-- This never gets called
})
----------EDIT----------
Adding MenuItemView, although viewModel.tapOnMenuItem gets always called, so I am not sure if it's very relevant
MenuItemView is here:
struct MenuItemView: View {
var item: MenuItem
#ObservedObject private var viewModel: MenuViewModel = MenuViewModel()
#State private var isSelected = false
var body: some View {
HStack(spacing: 24) {
Text(isSelected ? " 1 " : item.icon)
.font(.largeTitle)
.foregroundColor(.blue)
.bold()
VStack(alignment: .leading, spacing: 12) {
Text(item.name)
.bold()
Text(item.description)
.font(.callout)
}
Spacer()
Text("\(item.points)\npoints")
.multilineTextAlignment(.center)
}
.padding()
.onTapGesture {
self.isSelected = true
self.viewModel.tapOnMenuItem(self.item). // <-- Here tapOnMenuItem gets called
}
}
func quantityText(isItemSelected: Bool) -> String {
return isItemSelected ? "1" : item.icon
}
}
What am I doing wrong?

Answer 1

Well, here it is - your MenuView and MenuItemView use different instances of view model
1)
struct MenuView: View {
#ObservedObject private var viewModel: MenuViewModel
#State var showPicker = false
#State private var menu: Menu = Menu.mockMenu()
init(viewModel: MenuViewModel = MenuViewModel()) { // 1st one created
2)
struct MenuItemView: View {
var item: MenuItem
#ObservedObject private var viewModel: MenuViewModel = MenuViewModel() // 2nd one
thus, you modify one instance, but subscribe to changes in another one. That's it.
Solution: pass view model via .environmentObject or via argument from MenuView to MenuItemView.