I've created a property wrapper that I want to insert some logic into and the "set" value is doing the right thing, but the textfield isn't updating with all uppercase text. Shouldn't the text field be showing all uppercase text or am I misunderstanding how this is working?
Also this is a contrived example, my end goal is to insert a lot more logic into a property wrapper, I'm just using the uppercase example to get it working. I've searched all over the internet and haven't found a working solution.
import SwiftUI
import Combine
struct ContentView: View {
#StateObject var vm = FormDataViewModel()
var body: some View {
Form {
TextField("Name", text: $vm.name)
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
class FormDataViewModel: ObservableObject {
#Capitalized var name: String = ""
}
#propertyWrapper
public class Capitalized {
#Published var value: String
public var wrappedValue: String {
get { value }
set { value = newValue.uppercased() } //Printing this shows all caps
}
public var projectedValue: AnyPublisher<String, Never> {
return $value
.eraseToAnyPublisher()
}
public init(wrappedValue: String) {
value = wrappedValue
}
}
SwiftUI watches #Published properties in #StateObject or #ObservedObject and triggers UI update on changes of them.
But it does not go deep inside the ObservableObject. Your FormDataViewModel does not have any #Published properties.
One thing you can do is that simulating what #Published will do on value changes.
class FormDataViewModel: ObservableObject {
#Capitalized var name: String = ""
private var nameObserver: AnyCancellable?
init() {
nameObserver = _name.$value.sink {_ in
self.objectWillChange.send()
}
}
}
Please try.
This can be done with standard #Published that seems simpler and more reliable.
Here is a solution. Tested with Xcode 12 / iOS 14.
class FormDataViewModel: ObservableObject {
#Published var name: String = "" {
didSet {
let capitalized = name.uppercased()
if name != capitalized {
name = capitalized
objectWillChange.send()
}
}
}
}
When trying to compile the following code:
class LoginViewModel: ObservableObject, Identifiable {
#Published var mailAdress: String = ""
#Published var password: String = ""
#Published var showRegister = false
#Published var showPasswordReset = false
private let applicationStore: ApplicationStore
init(applicationStore: ApplicationStore) {
self.applicationStore = applicationStore
}
var passwordResetView: some View {
PasswordResetView(isPresented: $showPasswordReset) // This is where the error happens
}
}
Where PasswordResetView looks like this:
struct PasswordResetView: View {
#Binding var isPresented: Bool
#State var mailAddress: String = ""
var body: some View {
EmptyView()
}
}
}
I get the error compile error
Cannot convert value of type 'Published<Bool>.Publisher' to expected argument type 'Binding<Bool>'
If I use the published variable from outside the LoginViewModel class it just works fine:
struct LoginView: View {
#ObservedObject var viewModel: LoginViewModel
init(viewModel: LoginViewModel) {
self.viewModel = viewModel
}
var body: some View {
PasswordResetView(isPresented: self.$viewModel.showPasswordReset)
}
}
Any suggestions what I am doing wrong here? Any chance I can pass a published variable as a binding from inside the owning class?
Thanks!
Not sure why the proposed solutions here are so complex, when there is a very direct fix for this.
Found this answer on a similar Reddit question:
The problem is that you are accessing the projected value of an #Published (which is a Publisher) when you should instead be accessing the projected value of an #ObservedObject (which is a Binding), that is: you have globalSettings.$tutorialView where you should have $globalSettings.tutorialView.
** Still new to Combine & SwiftUI so not sure if there is better way to approach **
You can initalize Binding from publisher.
https://developer.apple.com/documentation/swiftui/binding/init(get:set:)-6g3d5
let binding = Binding(
get: { [weak self] in
(self?.showPasswordReset ?? false)
},
set: { [weak self] in
self?.showPasswordReset = $0
}
)
PasswordResetView(isPresented: binding)
I think the important thing to understand here is what "$" does in the Combine context.
What "$" does is to publish the changes of the variable "showPasswordReset" where it is being observed.
when it precedes a type, it doesn't represent the type you declared for the variable (Boolean in this case), it represents a publisher, if you want the value of the type, just remove the "$".
"$" is used in the context where a variable was marked as an #ObservedObject,
(the ObservableObject here is LoginViewModel and you subscribe to it to listen for changes in its variables market as publishers)
struct ContentView: View {
#ObservedObject var loginViewModel: LoginViewModel...
in that context (the ContentView for example) the changes of "showPasswordReset" are going to be 'Published' when its value is updated so the view is updated with the new value.
Here is possible approach - the idea to make possible observation in generated view and avoid tight coupling between factory & presenter.
Tested with Xcode 12 / iOS 14 (for older systems some tuning might be needed)
protocol ResetViewModel {
var showPasswordReset: Bool { get set }
}
struct PasswordResetView<Model: ResetViewModel & ObservableObject>: View {
#ObservedObject var resetModel: Model
var body: some View {
if resetModel.showPasswordReset {
Text("Show password reset")
} else {
Text("Show something else")
}
}
}
class LoginViewModel: ObservableObject, Identifiable, ResetViewModel {
#Published var mailAdress: String = ""
#Published var password: String = ""
#Published var showRegister = false
#Published var showPasswordReset = false
private let applicationStore: ApplicationStore
init(applicationStore: ApplicationStore) {
self.applicationStore = applicationStore
}
var passwordResetView: some View {
PasswordResetView(resetModel: self)
}
}
For error that states: "Cannot convert value of type 'Binding' to expected argument type 'Bool'" solution is to use wrappedValue as in example below.
If you have MyObject object with property isEnabled and you need to use that as vanilla Bool type instead of 'Binding' then do this
myView.disabled($myObject.isEnabled.wrappedValue)
I feel like I can sort of understand why what I'm doing isn't working but I'm still trying to wrap my head around Combine and SwiftUI so any help here would be welcome.
Consider this example:
Single view app that stores some strings in UserDefaults, and uses those strings to display some Text labels. There are three buttons, one to update the title, and one each to update the two UserDefaults-stored strings to a random string.
The view is a dumb renderer view and the title string is stored directly in an ObservableObject view model. The view model has a published property that holds a reference to a UserSettings class that implements property wrappers to store the user defined strings to UserDefaults.
Observations:
• Tapping "Set A New Title" correctly updates the view to show the new value
• Tapping either of the "Set User Value" buttons does change the value internally, however the view does not refresh.
If "Set A New Title" is tapped after one of these buttons, the new values are shown when the view body rebuilds for the title change.
View:
import SwiftUI
struct ContentView: View {
#ObservedObject var model = ViewModel()
var body: some View {
VStack {
Text(model.title).font(.largeTitle)
Form {
Section {
Text(model.settings.UserValue1)
Text(model.settings.UserValue2)
}
Section {
Button(action: {
self.model.title = "Updated Title"
}) { Text("Set A New Title") }
Button(action: {
self.model.settings.UserValue1 = "\(Int.random(in: 1...100))"
}) { Text("Set User Value 1 to Random Integer") }
Button(action: {
self.model.settings.UserValue2 = "\(Int.random(in: 1...100))"
}) { Text("Set User Value 2 to Random Integer") }
}
Section {
Button(action: {
self.model.settings.UserValue1 = "Initial Value One"
self.model.settings.UserValue2 = "Initial Value Two"
self.model.title = "Initial Title"
}) { Text("Reset All") }
}
}
}
}
}
ViewModel:
import Combine
class ViewModel: ObservableObject {
#Published var title = "Initial Title"
#Published var settings = UserSettings()
}
UserSettings model:
import Foundation
import Combine
#propertyWrapper struct DefaultsWritable<T> {
let key: String
let value: T
init(key: String, initialValue: T) {
self.key = key
self.value = initialValue
}
var wrappedValue: T {
get { return UserDefaults.standard.object(forKey: key) as? T ?? value }
set { return UserDefaults.standard.set(newValue, forKey: key) }
}
}
final class UserSettings: NSObject, ObservableObject {
let objectWillChange = PassthroughSubject<Void, Never>()
#DefaultsWritable(key: "UserValue", initialValue: "Initial Value One") var UserValue1: String {
willSet {
objectWillChange.send()
}
}
#DefaultsWritable(key: "UserBeacon2", initialValue: "Initial Value Two") var UserValue2: String {
willSet {
objectWillChange.send()
}
}
}
When I put a breakpoint on willSet { objectWillChange.send() } in UserSettings I see that the objectWillChange message is going to the publisher when I would expect it to so that tells me that the issue is likely that the view or the view model is not properly subscribing to it. I know that if I had UserSettings as an #ObservedObject on the view this would work, but I feel like this should be done in the view model with Combine.
What am I missing here? I'm sure it's really obvious...
ObsesrvedObject listens for changes in #Published property, but not the deeper internal publishers, so the below idea is to join internal publisher, which is PassthroughSubject, with #Published var settings, to indicate that the latter has updated.
Tested with Xcode 11.2 / iOS 13.2
The only needed changes is in ViewModel...
class ViewModel: ObservableObject {
#Published var title = "Initial Title"
#Published var settings = UserSettings()
private var cancellables = Set<AnyCancellable>()
init() {
self.settings.objectWillChange
.sink { _ in
self.objectWillChange.send()
}
.store(in: &cancellables)
}
}
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
I'm trying to execute an action every time a textField's value is changed.
#Published var value: String = ""
var body: some View {
$value.sink { (val) in
print(val)
}
return TextField($value)
}
But I get below error.
Cannot convert value of type 'Published' to expected argument type 'Binding'
This should be a non-fragile way of doing it:
class MyData: ObservableObject {
var value: String = "" {
willSet(newValue) {
print(newValue)
}
}
}
struct ContentView: View {
#ObservedObject var data = MyData()
var body: some View {
TextField("Input:", text: $data.value)
}
}
In your code, $value is a publisher, while TextField requires a binding. While you can change from #Published to #State or even #Binding, that can't observe the event when the value is changed.
It seems like there is no way to observe a binding.
An alternative is to use ObservableObject to wrap your value type, then observe the publisher ($value).
class MyValue: ObservableObject {
#Published var value: String = ""
init() {
$value.sink { ... }
}
}
Then in your view, you have have the binding $viewModel.value.
struct ContentView: View {
#ObservedObject var viewModel = MyValue()
var body: some View {
TextField($viewModel.value)
}
}
I don't use combine for this. This it's working for me:
TextField("write your answer here...",
text: Binding(
get: {
return self.query
},
set: { (newValue) in
self.fetch(query: newValue) // any action you need
return self.query = newValue
}
)
)
I have to say it's not my idea, I read it in this blog: SwiftUI binding: A very simple trick
If you want to observe value then it should be a State
#State var value: String = ""
You can observe TextField value by using ways,
import SwiftUI
import Combine
struct ContentView: View {
#State private var Text1 = ""
#State private var Text2 = ""
#ObservedObject var viewModel = ObserveTextFieldValue()
var body: some View {
//MARK: TextField with Closures
TextField("Enter text1", text: $Text1){
editing in
print(editing)
}onCommit: {
print("Committed")
}
//MARK: .onChange Modifier
TextField("Enter text2", text: $Text2).onChange(of: Text2){
text in
print(text)
}
//MARK: ViewModel & Publisher(Combine)
TextField("Enter text3", text: $viewModel.value)
}
}
class ObserveTextFieldValue: ObservableObject {
#Published var value: String = ""
private var cancellables = Set<AnyCancellable>()
init() {
$value.sink(receiveValue: {
val in
print(val)
}).store(in: &cancellables)
}
}
#Published is one of the most useful property wrappers in SwiftUI, allowing us to create observable objects that automatically announce when changes occur that means whenever an object with a property marked #Published is changed, all views using that object will be reloaded to reflect those changes.
import SwiftUI
struct ContentView: View {
#ObservedObject var textfieldData = TextfieldData()
var body: some View {
TextField("Input:", text: $textfieldData.data)
}
}
class TextfieldData: ObservableObject{
#Published var data: String = ""
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}