I have 2 views where the
first view passes list of items and selected item in that to second view and
second view returns the updated selected item if user changes.
I am getting error 'Type of expression is ambiguous without more context' when i am sending the model property 'idx'.
//I cant make any changes to this model so cant confirm it with ObservableObject or put a bool property like 'isSelected'
class Model {
var idx: String?
....
}
class FirstViewModel: ObservableObject {
var list: [Model]
#Published var selectedModel: Model?
func getSecondViewModel() -> SecondViewModel {
let vm2 = SecondViewModel( //error >> Type of expression is ambiguous without more context
list: list,
selected: selectedModel?.idx // >> issue might be here but showing at above line
)
return vm2
}
}
struct FirstView: View {
#ObservableObject firstViewModel: FirstViewModel
var body: some View {
..
.sheet(isPresented: $showView2) {
NavigationView {
SecondView(viewModel: firstViewModel.getSecondViewModel())
}
}
..
}
}
class SecondViewModel: ObservableObject {
var list: [Model]
#Published var selected: String?
init(list: [Model], selected: Published<String?>) {
self.list = list
_selected = selected
}
func setSelected(idx: String) {
self.selected = idx
}
}
struct SecondView: View {
#ObservableObject secondViewModel: SecondViewModel
#Environment(\.presentationMode) var presentationMode
var body: some View {
...
.onTapGesture {
secondViewModel.setSelected(idx: selectedIndex)
presentationMode.wrappedValue.dismiss()
}
...
}
}
In case if I am sending 'Model' object directly to the SecondViewModel its working fine. I need to make changes the type and couple of other areas and instantiate the SecondViewModel as below
let vm2 = SecondViewModel(
list: list,
selected: _selectedModel
)
Since I need only idx I don't want to send entire model.
Also the reason for error might be but not sure the Model is #Published and the idx is not.
Any help is appreciated
Here is some code, in keeping with your original code that allows you to
use the secondViewModel as a nested model.
It passes firstViewModel to the SecondView, because
secondViewModel is contained in the firstViewModel. It also uses
firstViewModel.objectWillChange.send() to tell the model to update.
My comment is still valid, you need to create only one SecondViewModel that you use. Currently, your func getSecondViewModel() returns a new SecondViewModel every time you use it.
Re-structure your code so that you do not need to have nested ObservableObjects.
struct Model {
var idx = ""
}
struct ContentView: View {
#StateObject var firstMdl = FirstViewModel()
var body: some View {
VStack (spacing: 55){
FirstView(firstViewModel: firstMdl)
Text(firstMdl.secondViewModel.selected ?? "secondViewModel NO selected data")
}
}
}
class FirstViewModel: ObservableObject {
var list: [Model]
#Published var selectedModel: Model?
let secondViewModel: SecondViewModel // <-- here only one source of truth
// -- here
init() {
self.list = []
self.selectedModel = nil
self.secondViewModel = SecondViewModel(list: list, selected: nil)
}
// -- here
func getSecondViewModel() -> SecondViewModel {
secondViewModel.selected = selectedModel?.idx
return secondViewModel
}
}
class SecondViewModel: ObservableObject {
var list: [Model]
#Published var selected: String?
init(list: [Model], selected: String?) { // <-- here
self.list = list
self.selected = selected // <-- here
}
func setSelected(idx: String) {
selected = idx
}
}
struct FirstView: View {
#ObservedObject var firstViewModel: FirstViewModel // <-- here
#State var showView2 = false
var body: some View {
Button("click me", action: {showView2 = true}).padding(20).border(.green)
.sheet(isPresented: $showView2) {
SecondView(firstViewModel: firstViewModel)
}
}
}
struct SecondView: View {
#ObservedObject var firstViewModel: FirstViewModel // <-- here
#Environment(\.dismiss) var dismiss
#State var selectedIndex = "---> have some data now"
var body: some View {
Text("SecondView tap here to dismiss").padding(20).border(.red)
.onTapGesture {
firstViewModel.objectWillChange.send() // <-- here
firstViewModel.getSecondViewModel().setSelected(idx: selectedIndex) // <-- here
// alternatively
// firstViewModel.secondViewModel.selected = selectedIndex
dismiss()
}
}
}
I think I've a gap in understanding what exactly #State means, especially when it comes to displaying contents from a ForEach loop.
My scenario: I've created minimum reproducible example. Below is a parent view with a ForEach loop. Each child view has aNavigationLink.
// Parent code which passes a Course instance down to the child view - i.e. CourseView
struct ContentView: View {
#StateObject private var viewModel: ViewModel = .init()
var body: some View {
NavigationView {
VStack {
ForEach(viewModel.courses) { course in
NavigationLink(course.name + " by " + course.instructor) {
CourseView(course: course, viewModel: viewModel)
}
}
}
}
}
}
class ViewModel: ObservableObject {
#Published var courses: [Course] = [
Course(name: "CS101", instructor: "John"),
Course(name: "NS404", instructor: "Daisy")
]
}
struct Course: Identifiable {
var id: String = UUID().uuidString
var name: String
var instructor: String
}
Actual Dilemma: I've tried two variations for the CourseView, one with let constant and another with a #State var for the course field. Additional comments in the code below.
The one with the let constant successfully updates the child view when the navigation link is open. However, the one with #State var doesn't update the view.
struct CourseView: View {
// Case 1: Using let constant (works as expected)
let course: Course
// Case 2: Using #State var (doesn't update the UI)
// #State var course: Course
#ObservedObject var viewModel: ViewModel
var body: some View {
VStack {
Text("\(course.name) by \(course.instructor)")
Button("Edit Instructor", action: editInstructor)
}
}
// Case 1: It works and UI gets updated
// Case 2: Doesn't work as is.
// I've to directly update the #State var instead of updating the clone -
// which sometimes doesn't update the var in my actual project
// (that I'm trying to reproduce). It definitely works here though.
private func editInstructor() {
let instructor = course.instructor == "Bob" ? "John" : "Bob"
var course = course
course.instructor = instructor
save(course)
}
// Simulating a database save, akin to something like GRDB
// Here, I'm just updating the array to see if ForEach picks up the changes
private func save(_ courseToSave: Course) {
guard let index = viewModel.courses.firstIndex(where: { $0.id == course.id }) else {
return
}
viewModel.courses[index] = courseToSave
}
}
What I'm looking for is the best practice for a scenario where looping through an array of models is required and the model is updated in DB from within the child view.
Here is a right way for you, do not forget that we do not need put logic in View! the view should be dummy as possible!
struct ContentView: View {
#StateObject private var viewModel: ViewModel = ViewModel.shared
var body: some View {
NavigationView {
VStack {
ForEach(viewModel.courses) { course in
NavigationLink(course.name + " by " + course.instructor, destination: CourseView(course: course, viewModel: viewModel))
}
}
}
}
}
struct CourseView: View {
let course: Course
#ObservedObject var viewModel: ViewModel
var body: some View {
VStack {
Text("\(course.name) by \(course.instructor)")
Button("Update Instructor", action: { viewModel.update(course) })
}
}
}
class ViewModel: ObservableObject {
static let shared: ViewModel = ViewModel()
#Published var courses: [Course] = [
Course(name: "CS101", instructor: "John"),
Course(name: "NS404", instructor: "Daisy")
]
func update(_ course: Course) {
guard let index = courses.firstIndex(where: { $0.id == course.id }) else {
return
}
courses[index] = Course(name: course.name, instructor: (course.instructor == "Bob") ? "John" : "Bob")
}
}
struct Course: Identifiable {
let id: String = UUID().uuidString
var name: String
var instructor: String
}
I have a simple use case of having a VStack of a dynamic number of Text with Toggle buttons coming from an array.
import SwiftUI
public struct Test: View {
#ObservedObject public var viewModel = TestViewModel()
public init() {
}
public var body: some View {
VStack {
ForEach(viewModel.models) { model in
ToggleView(title: <#T##Binding<String>#>, switchState: <#T##Binding<Bool>#>)
//how to add the above
}
}.padding(50)
}
}
struct ToggleView: View {
#Binding var title: String
#Binding var switchState: Bool
var body: some View {
VStack {
Toggle(isOn: $switchState) {
Text(title)
}
}
}
}
public class TestModel: Identifiable {
#Published var state: Bool {
didSet {
//do something
//publish to the view that the state has changed
}
}
#Published var title: String
init(state: Bool, title: String) {
self.state = state
self.title = title
}
}
public class TestViewModel: ObservableObject {
#Published var models: [TestModel] = [TestModel(state: false, title: "Title 1"), TestModel(state: true, title: "Title 2")]
}
The following questions arise:
In MVVM pattern, is it ok to have the binding variables in model class or should it be inside the view model?
How to send the message of state change from model class to view/scene when the toggle state is changed?
If using an array of binding variables in view model for each of the toggle states, how to know which particular element of array has changed? (see the following code snippet)
class ViewModel {
#Published var dataModel: [TestModel]
#Published var toggleStates = [Bool]() {
didSet {
//do something based on which element of the toggle states array has changed
}
}
}
Please help with the above questions.
here is one way you could achieve what you desire.
Has you will notice you have to use the binding power of #ObservedObject.
The trick is to use indexes to reach the array elements for you binding.
If you loop on the array elements model directly you loose the underlying binding properties.
struct Test: View {
#ObservedObject public var viewModel = TestViewModel()
var body: some View {
VStack {
ForEach(viewModel.models.indices) { index in
ToggleView(title: self.viewModel.models[index].title, switchState: self.$viewModel.models[index].state)
}
}.padding(50)
}
}
class TestViewModel: ObservableObject {
#Published var models: [TestModel] = [
TestModel(state: false, title: "Title 1"),
TestModel(state: true, title: "Title 2")]
}
struct ToggleView: View {
var title: String
#Binding var switchState: Bool
var body: some View {
VStack {
Toggle(isOn: $switchState) {
Text(title)
}
}
}
}
class TestModel: Identifiable {
var state: Bool
var title: String
init(state: Bool, title: String) {
self.title = title
self.state = state
}
}
Hope this does the trick for you.
Best
I have a SwiftUI view that takes in an EnvironmentObject called appModel. It then reads the value appModel.submodel.count in its body method. I expect this to bind my view to the property count on submodel so that it re-renders when the property updates, but this does not seem to happen.
Is this a bug? And if not, what is the idiomatic way to have views bind to nested properties of environment objects in SwiftUI?
Specifically, my model looks like this...
class Submodel: ObservableObject {
#Published var count = 0
}
class AppModel: ObservableObject {
#Published var submodel: Submodel = Submodel()
}
And my view looks like this...
struct ContentView: View {
#EnvironmentObject var appModel: AppModel
var body: some View {
Text("Count: \(appModel.submodel.count)")
.onTapGesture {
self.appModel.submodel.count += 1
}
}
}
When I run the app and click on the label, the count property does increase but the label does not update.
I can fix this by passing in appModel.submodel as a property to ContentView, but I'd like to avoid doing so if possible.
Nested models does not work yet in SwiftUI, but you could do something like this
class SubModel: ObservableObject {
#Published var count = 0
}
class AppModel: ObservableObject {
#Published var submodel: SubModel = SubModel()
var anyCancellable: AnyCancellable? = nil
init() {
anyCancellable = submodel.objectWillChange.sink { [weak self] (_) in
self?.objectWillChange.send()
}
}
}
Basically your AppModel catches the event from SubModel and send it further to the View.
Edit:
If you do not need SubModel to be class, then you could try something like this either:
struct SubModel{
var count = 0
}
class AppModel: ObservableObject {
#Published var submodel: SubModel = SubModel()
}
Sorin Lica's solution can solve the problem but this will result in code smell when dealing with complicated views.
What seems to better advice is to look closely at your views, and revise them to make more, and more targeted views. Structure your views so that each view displays a single level of the object structure, matching views to the classes that conform to ObservableObject. In the case above, you could make a view for displaying Submodel (or even several views) that display's the property from it that you want show. Pass the property element to that view, and let it track the publisher chain for you.
struct ContentView: View {
#EnvironmentObject var appModel: AppModel
var body: some View {
SubView(submodel: appModel.submodel)
}
}
struct SubView: View {
#ObservedObject var submodel: Submodel
var body: some View {
Text("Count: \(submodel.count)")
.onTapGesture {
self.submodel.count += 1
}
}
}
This pattern implies making more, smaller, and focused views, and lets the engine inside SwiftUI do the relevant tracking. Then you don't have to deal with the book keeping, and your views potentially get quite a bit simpler as well.
You can check for more detail in this post: https://rhonabwy.com/2021/02/13/nested-observable-objects-in-swiftui/
I wrote about this recently on my blog: Nested Observable Objects. The gist of the solution, if you really want a hierarchy of ObservableObjects, is to create your own top-level Combine Subject to conform to the ObservableObject protocol, and then encapsulate any logic of what you want to trigger updates into imperative code that updates that subject.
For example, if you had two "nested" classes, such as
class MainThing : ObservableObject {
#Published var element : SomeElement
init(element : SomeElement) {
self.element = element
}
}
class SomeElement : ObservableObject {
#Published var value : String
init(value : String) {
self.value = value
}
}
Then you could expand the top-level class (MainThing in this case) to:
class MainThing : ObservableObject {
#Published var element : SomeElement
var cancellable : AnyCancellable?
init(element : SomeElement) {
self.element = element
self.cancellable = self.element.$value.sink(
receiveValue: { [weak self] _ in
self?.objectWillChange.send()
}
)
}
}
Which grabs a publisher from the embedded ObservableObject, and sends an update into the local published when the property value on SomeElement class is modified. You can extend this to use CombineLatest for publishing streams from multiple properties, or any number of variations on the theme.
This isn't a "just do it" solution though, because the logical conclusion of this pattern is after you've grown that hierarchy of views, you're going to end up with potentially huge swatches of a View subscribed to that publisher that will invalidate and redraw, potentially causing excessive, sweeping redraws and relatively poor performance on updates. I would advise seeing if you can refactor your views to be specific to a class, and match it to just that class, to keep the "blast radius" of SwiftUI's view invalidation minimized.
#Published is not designed for reference types so it's a programming error to add it on the AppModel property, even though the compiler or runtime doesn't complain. What would've been intuitive is adding #ObservedObject like below but sadly this silently does nothing:
class AppModel: ObservableObject {
#ObservedObject var submodel: SubModel = SubModel()
}
I'm not sure if disallowing nested ObservableObjects was intentional by SwiftUI or a gap to be filled in the future. Wiring up the parent and child objects as suggested in the other answers is very messy and hard to maintain. What seems to be the idea of SwiftUI is to split up the views into smaller ones and pass the child object to the subview:
struct ContentView: View {
#EnvironmentObject var appModel: AppModel
var body: some View {
SubView(model: appModel.submodel)
}
}
struct SubView: View {
#ObservedObject var model: SubModel
var body: some View {
Text("Count: \(model.count)")
.onTapGesture {
model.count += 1
}
}
}
class SubModel: ObservableObject {
#Published var count = 0
}
class AppModel: ObservableObject {
var submodel: SubModel = SubModel()
}
The submodel mutations actually propagate when passing into a subview!
However, there's nothing stopping another dev from calling appModel.submodel.count from the parent view which is annoying there's no compiler warning or even some Swift way to enforce not doing this.
Source: https://rhonabwy.com/2021/02/13/nested-observable-objects-in-swiftui/
If you need to nest observable objects here is the best way to do it that I could find.
class ChildModel: ObservableObject {
#Published
var count = 0
}
class ParentModel: ObservableObject {
#Published
private var childWillChange: Void = ()
let child = ChildModel()
init() {
child.objectWillChange.assign(to: &$childWillChange)
}
}
Instead of subscribing to child's objectWillChange publisher and firing parent's publisher, you assign values to published property and parent's objectWillChange triggers automatically.
All three ViewModels can communicate and update
// First ViewModel
class FirstViewModel: ObservableObject {
var facadeViewModel: FacadeViewModels
facadeViewModel.firstViewModelUpdateSecondViewModel()
}
// Second ViewModel
class SecondViewModel: ObservableObject {
}
// FacadeViewModels Combine Both
import Combine // so you can update thru nested Observable Objects
class FacadeViewModels: ObservableObject {
lazy var firstViewModel: FirstViewModel = FirstViewModel(facadeViewModel: self)
#Published var secondViewModel = secondViewModel()
}
var anyCancellable = Set<AnyCancellable>()
init() {
firstViewModel.objectWillChange.sink {
self.objectWillChange.send()
}.store(in: &anyCancellable)
secondViewModel.objectWillChange.sink {
self.objectWillChange.send()
}.store(in: &anyCancellable)
}
func firstViewModelUpdateSecondViewModel() {
//Change something on secondViewModel
secondViewModel
}
Thank you Sorin for Combine solution.
I have a solution that I believe is more ellegant than subscribing to the child (view)models. It's weird and I don't have an explanation for why it works.
Solution
Define a base class that inherits from ObservableObject, and defines a method notifyWillChange() that simply calls objectWillChange.send(). Any derived class then overrides notifyWillChange() and calls the parent's notifyWillChange() method.
Wrapping objectWillChange.send() in a method is required, otherwise the changes to #Published properties do not cause the any Views to update. It may have something to do with how #Published changes are detected. I believe SwiftUI/Combine use reflection under the hood...
I have made some slight additions to OP's code:
count is wrapped in a method call which calls notifyWillChange() before the counter is incremented. This is required for the propagation of the changes.
AppModel contains one more #Published property, title, which is used for the navigation bar's title. This showcases that #Published works for both the parent object and the child (in the example below, updated 2 seconds after the model is initialized).
Code
Base Model
class BaseViewModel: ObservableObject {
func notifyWillUpdate() {
objectWillChange.send()
}
}
Models
class Submodel: BaseViewModel {
#Published var count = 0
}
class AppModel: BaseViewModel {
#Published var title: String = "Hello"
#Published var submodel: Submodel = Submodel()
override init() {
super.init()
DispatchQueue.main.asyncAfter(deadline: .now() + 2) { [weak self] in
guard let self = self else { return }
self.notifyWillChange() // XXX: objectWillChange.send() doesn't work!
self.title = "Hello, World"
}
}
func increment() {
notifyWillChange() // XXX: objectWillChange.send() doesn't work!
submodel.count += 1
}
override func notifyWillChange() {
super.notifyWillChange()
objectWillChange.send()
}
}
The View
struct ContentView: View {
#EnvironmentObject var appModel: AppModel
var body: some View {
NavigationView {
Text("Count: \(appModel.submodel.count)")
.onTapGesture {
self.appModel.increment()
}.navigationBarTitle(appModel.title)
}
}
}
I liked solution by sorin-lica. Based upon that I've decided to implement a custom Property Wrapper (following this amazing article) named NestedObservableObject to make that solution more developer friendly.
This allow to write your model in the following way
class Submodel: ObservableObject {
#Published var count = 0
}
class AppModel: ObservableObject {
#NestedObservableObject var submodel: Submodel = Submodel()
}
Property Wrapper implementation
#propertyWrapper
struct NestedObservableObject<Value : ObservableObject> {
static subscript<T: ObservableObject>(
_enclosingInstance instance: T,
wrapped wrappedKeyPath: ReferenceWritableKeyPath<T, Value>,
storage storageKeyPath: ReferenceWritableKeyPath<T, Self>
) -> Value {
get {
if instance[keyPath: storageKeyPath].cancellable == nil, let publisher = instance.objectWillChange as? ObservableObjectPublisher {
instance[keyPath: storageKeyPath].cancellable =
instance[keyPath: storageKeyPath].storage.objectWillChange.sink { _ in
publisher.send()
}
}
return instance[keyPath: storageKeyPath].storage
}
set {
if let cancellable = instance[keyPath: storageKeyPath].cancellable {
cancellable.cancel()
}
if let publisher = instance.objectWillChange as? ObservableObjectPublisher {
instance[keyPath: storageKeyPath].cancellable =
newValue.objectWillChange.sink { _ in
publisher.send()
}
}
instance[keyPath: storageKeyPath].storage = newValue
}
}
#available(*, unavailable,
message: "This property wrapper can only be applied to classes"
)
var wrappedValue: Value {
get { fatalError() }
set { fatalError() }
}
private var cancellable: AnyCancellable?
private var storage: Value
init(wrappedValue: Value) {
storage = wrappedValue
}
}
I've published code on gist
I do it like this:
import Combine
extension ObservableObject {
func propagateWeakly<InputObservableObject>(
to inputObservableObject: InputObservableObject
) -> AnyCancellable where
InputObservableObject: ObservableObject,
InputObservableObject.ObjectWillChangePublisher == ObservableObjectPublisher
{
objectWillChange.propagateWeakly(to: inputObservableObject)
}
}
extension Publisher where Failure == Never {
public func propagateWeakly<InputObservableObject>(
to inputObservableObject: InputObservableObject
) -> AnyCancellable where
InputObservableObject: ObservableObject,
InputObservableObject.ObjectWillChangePublisher == ObservableObjectPublisher
{
sink { [weak inputObservableObject] _ in
inputObservableObject?.objectWillChange.send()
}
}
}
So on the call side:
class TrackViewModel {
private let playbackViewModel: PlaybackViewModel
private var propagation: Any?
init(playbackViewModel: PlaybackViewModel) {
self.playbackViewModel = playbackViewModel
propagation = playbackViewModel.propagateWeakly(to: self)
}
...
}
Here's a gist.
See following post for a solution: [arthurhammer.de/2020/03/combine-optional-flatmap][1] . This is solving the question in a Combine-Way with the $ publisher.
Assume class Foto has an annotation struct and and annotation publisher, which publish an annotation struct. Within Foto.sample(orientation: .Portrait) the annotation struct gets "loaded" through the annotation publisher asynchroniously. Plain vanilla combine.... but to get that into a View & ViewModel, use this:
class DataController: ObservableObject {
#Published var foto: Foto
#Published var annotation: LCPointAnnotation
#Published var annotationFromFoto: LCPointAnnotation
private var cancellables: Set<AnyCancellable> = []
init() {
self.foto = Foto.sample(orientation: .Portrait)
self.annotation = LCPointAnnotation()
self.annotationFromFoto = LCPointAnnotation()
self.foto.annotationPublisher
.replaceError(with: LCPointAnnotation.emptyAnnotation)
.assign(to: \.annotation, on: self)
.store(in: &cancellables)
$foto
.flatMap { $0.$annotation }
.replaceError(with: LCPointAnnotation.emptyAnnotation)
.assign(to: \.annotationFromFoto, on: self)
.store(in: &cancellables)
}
}
Note: [1]: https://arthurhammer.de/2020/03/combine-optional-flatmap/
Pay attention the $annotation above within the flatMap, it's a publisher!
public class Foto: ObservableObject, FotoProperties, FotoPublishers {
/// use class not struct to update asnyc properties!
/// Source image data
#Published public var data: Data
#Published public var annotation = LCPointAnnotation.defaultAnnotation
......
public init(data: Data) {
guard let _ = UIImage(data: data),
let _ = CIImage(data: data) else {
fatalError("Foto - init(data) - invalid Data to generate CIImage or UIImage")
}
self.data = data
self.annotationPublisher
.replaceError(with: LCPointAnnotation.emptyAnnotation)
.sink {resultAnnotation in
self.annotation = resultAnnotation
print("Foto - init annotation = \(self.annotation)")
}
.store(in: &cancellables)
}
You can create a var in your top view that is equal to a function or published var in your top class. Then pass it and bind it to every sub view. If it changes in any sub view then the top view will be updated.
Code Structure:
struct Expense : Identifiable {
var id = UUID()
var name: String
var type: String
var cost: Double
var isDeletable: Bool
}
class Expenses: ObservableObject{
#Published var name: String
#Published var items: [Expense]
init() {
name = "John Smith"
items = [
Expense(name: "Lunch", type: "Business", cost: 25.47, isDeletable: true),
Expense(name: "Taxi", type: "Business", cost: 17.0, isDeletable: true),
Expense(name: "Sports Tickets", type: "Personal", cost: 75.0, isDeletable: false)
]
}
func totalExpenses() -> Double { }
}
class ExpenseTracker: ObservableObject {
#Published var name: String
#Published var expenses: Expenses
init() {
name = "My name"
expenses = Expenses()
}
func getTotalExpenses() -> Double { }
}
Views:
struct MainView: View {
#ObservedObject var myTracker: ExpenseTracker
#State var totalExpenses: Double = 0.0
var body: some View {
NavigationView {
Form {
Section (header: Text("Main")) {
HStack {
Text("name:")
Spacer()
TextField("", text: $myTracker.name)
.multilineTextAlignment(.trailing)
.keyboardType(.default)
}
NavigationLink(destination: ContentView(myExpenses: myTracker.expenses, totalExpenses: $totalExpenses),
label: {
Text("View Expenses")
})
}
Section (header: Text("Results")) {
}
HStack {
Text("Total Expenses")
Spacer()
Text("\(totalExpenses, specifier: "%.2f")")
}
}
}
.navigationTitle("My Expense Tracker")
.font(.subheadline)
}
.onAppear{
totalExpenses = myTracker.getTotalExpenses()
}
}
}
struct ContentView: View {
#ObservedObject var myExpenses:Expenses
#Binding var totalExpenses: Double
#State var selectedExpenseItem:Expense? = nil
var body: some View {
NavigationView{
Form {
List {
ForEach(myExpenses.items) { item in
HStack {
Text("\(item.name)")
Spacer()
Button(action: {
self.selectedExpenseItem = item
} ) {
Text("View")
}
}
.deleteDisabled(item.isDeletable)
}
.onDelete(perform: removeItem)
}
HStack {
Text("Total Expenses:")
Spacer()
Text("\(myExpenses.totalExpenses(), specifier: "%.2f")")
}
}
.navigationTitle("Expenses")
.toolbar {
Button {
let newExpense = Expense(name: "Enter name", type: "Expense item", cost: 10.00, isDeletable: false)
self.myExpenses.items.append(newExpense)
self.totalExpenses = myExpenses.totalExpenses()
} label: {
Image(systemName: "plus")
}
}
}
.fullScreenCover(item: $selectedExpenseItem) { myItem in
ItemDetailView(item: myItem, myExpenses: myExpenses, totalExpenses: $totalExpenses)
}
}
func removeItem(at offsets: IndexSet){
self.myExpenses.items.remove(atOffsets: offsets)
self.totalExpenses = myExpenses.totalExpenses()
}
}
Just noting that I'm using the NestedObservableObject approach from #bsorrentino in my latest app.
Normally I'd avoid this but the nested object in question is actually a CoreData model so breaking things out into smaller views doesn't really work in this regard.
This solution seemed best since the world treats NSManagedObjects as (mostly) ObservableObjects and I really, really need to trigger an update if the CodeData object model is changed down the line.
The var submodel in AppModel doesn't need the property wrapper #Published.
The purpose of #Published is to emit new values and objectWillChange.
But the variable is never changed but only initiated once.
Changes in submodel are propagated to the view by the subscriber anyCancellable and ObservableObject-protocol via the sink-objectWillChange construction and causes a View to redraw.
class SubModel: ObservableObject {
#Published var count = 0
}
class AppModel: ObservableObject {
let submodel = SubModel()
var anyCancellable: AnyCancellable? = nil
init() {
anyCancellable = submodel.objectWillChange.sink { [weak self] (_) in
self?.objectWillChange.send()
}
}
}
Nested ObservableObject models do not work yet.
However, you can make it work by manually subscribing each model. The answer gave a simple example of this.
I wanted to add that you can make this manual process a bit more streamlined & readable via extensions:
class Submodel: ObservableObject {
#Published var count = 0
}
class AppModel: ObservableObject {
#Published var submodel = Submodel()
#Published var submodel2 = Submodel2() // the code for this is not defined and is for example only
private var cancellables: Set<AnyCancellable> = []
init() {
// subscribe to changes in `Submodel`
submodel
.subscribe(self)
.store(in: &cancellables)
// you can also subscribe to other models easily (this solution scales well):
submodel2
.subscribe(self)
.store(in: &cancellables)
}
}
Here is the extension:
extension ObservableObject where Self.ObjectWillChangePublisher == ObservableObjectPublisher {
func subscribe<T: ObservableObject>(
_ observableObject: T
) -> AnyCancellable where T.ObjectWillChangePublisher == ObservableObjectPublisher {
return objectWillChange
// Publishing changes from background threads is not allowed.
.receive(on: DispatchQueue.main)
.sink { [weak observableObject] (_) in
observableObject?.objectWillChange.send()
}
}
}
It looks like bug. When I update the xcode to the latest version, it work correctly when binding to nested ObservableObjects
Im using the new SwiftUI. I have a UserUpdate class which is a Bindable Object and I want to modify these variables and automatically Update the UI.
I update these Values successfully but the views in my UI struct isn't updating when I change the variable in the UserUpdate class.
It only changes when I modify the #EnviromentObject variable in the UI struct itself.
That's my Bindable Object Class:
final class UserUpdate: BindableObject {
let didChange = PassthroughSubject<Any, Never>()
var allUsers: [User] = [] {
didSet {
print(allUsers)
didChange.send(allUsers)
}
}
var firstName: String = "" {
didSet {
didChange.send(firstName)
}
}
var lastName: String = "" {
didSet {
didChange.send(lastName)
}
}
}
That's my User class:
struct User: Identifiable {
let id: Int
let firstName, lastName: String
}
Here's how I configure my UI:
struct ContentView : View {
#EnvironmentObject var bindableUser: UserUpdate
var body: some View {
NavigationView {
VStack(alignment: .leading) {
Text("All Users:").bold().padding(.leading, 10)
List {
ForEach(bindableUser.allUsers) { user in
Text("\(user.firstName) \(user.lastName)")
}
}
}
}
}
}
Here I modify the variables in UserUpdate:
class TestBind {
static let instance = TestBind()
let userUpdate = UserUpdate()
func bind() {
let user = User(id: userUpdate.allUsers.count, firstName: "Heyy", lastName: "worked")
userUpdate.allUsers.append(user)
}
}
I found out that I had to call the method from my UI to get it working so its on the same stream.
For example by this:
struct ContentView : View {
#EnvironmentObject var networkManager: NetworkManager
var body: some View {
VStack {
Button(action: {
self.networkManager.getAllCourses()
}, label: {
Text("Get All Courses")
})
List(networkManager.courses.identified(by: \.name)) {
Text($0.name)
}
}
}
}
If I'm not wrong, you should inject the UserUpdate instance in your ContentView, probably in the SceneDelegate, using ContentView().environmentObject(UserUpdate()).
In that case, you have 2 different instance of the UserUpdate class, the first one created in the SceneDelegate, and the second created in the TestBind class.
The problem is that you have one instance that is bond to view (and will trigger view reload on update), and the one that you actually modify (in TestBind class) which is totally unrelated to the view.
You should find a way to use the same instance in the view and in the TestBind class (for example by using ContentView().environmentObject(TestBind.instance.userUpdate)