Publishing changes to a collection of observable objects - swift

I have an issue with propagating changes that happen to objects in the view model that are kept in an array.
I understand that #Published for a collection would work if the collection itself changes (eg. if elements were struct not class). Assuming that I need to preserve classes as classes. Is there a way to propagate events to a view, so that it knows it should be refreshed.
I have been trying all nasty ways like implementing ObservableCollection or ObservableArray but nothing seems to work.
Below an example of what I am struggling with.
Toggle is changing internally element of an array which has all the ObservableObject conformance and #Published annotation but still Text is not being refreshed.
import SwiftUI
import Combine
struct ContentView: View {
#StateObject var vm = ViewModel()
var body: some View {
Text(vm.texts.first!.text)
.padding()
Button("Toggle") {
vm.texts.first?.toggle()
}
}
}
class ViewModel: ObservableObject {
#Published var texts: [TextHolder] = [.init(), .init()]
}
class TextHolder: ObservableObject {
#Published var text: String = ""
func toggle() {
text = UUID().uuidString
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}

Problem with your approach is that TextHolder is a class, which is reference type, if you change any value in it, changes won't reflect to array that's why SwiftUI view is not updated.
Approach 1:
You can change TextHolder from class to struct, if you change any value in struct a new copy is created, your array will get the change to as your SwiftUI view.
Please try below code
struct ContentView: View {
#StateObject var vm = ViewModel()
var body: some View {
Text(vm.texts.first!.text)
.padding()
Button("Toggle") {
vm.texts[0].toggle()
}
}
}
class ViewModel: ObservableObject {
#Published var texts: [TextHolder] = [.init(), .init()]
}
struct TextHolder {
var text: String = ""
mutating func toggle() {
text = UUID().uuidString
}
}
Approach 2:
After changing value you have to manually tell your viewModel that something is changed, please refresh.
Button("Toggle") {
vm.texts[0].toggle()
vm.objectWillChange.send()
}
Hope it will help you to understand.

Note: this is based on the requirement you listed of "Assuming that I need to preserve classes as classes" -- otherwise, making your model a struct gives you all of this behavior for free.
You can call objectWillChange.send() manually on the ObservableObject. For example:
Button("Toggle") {
vm.texts.first?.toggle()
vm.objectWillChange.send()
}
Major downsides include having to add code to call this at each mutation site and actually remembering to do this. You could do things to compartmentalize the code a little more like moving toggle to the parent object and passing an index to it -- then, you could keep all of the objectWillChange calls in the parent. Also, you could experiment with KVO to watch the properties of the child objects and call objectWillChange when you see one of them change.

If you are not able to convert the class to a struct, an approach you can take is to subscribe to all objectWillChange publishers of the items in the array, and emit one for the main model, when one of those objects change:
#Published var texts: [TextHolder] = [.init(), .init()] {
didSet {
updateTextsSubscriptions()
}
}
private var textsSubscriptions = [AnyCancellable]()
private func updateTextsSubscriptions() {
textsSubscriptions = texts.map {
$0.objectWillChange.sink(receiveValue: {
self.objectWillChange.send()
})
}
}
You will also need to call updateTextsSubscriptions from within the initializer(s), to make sure any initial values for the texts array are monitored:
init() {
updateTextsSubscriptions()
}

Related

How can I call a function of a child view from the parent view in swiftUI to change a #state variable?

I'm trying to get into swift/swiftui but I'm really struggling with this one:
I have a MainView containing a ChildView. The ChildView has a function update to fetch the data to display from an external source and assign it to a #State data variable.
I'd like to be able to trigger update from MainView in order to update data.
I've experienced that update is in fact called, however, data is reset to the initial value upon this call.
The summary of what I have:
struct ChildView: View {
#State var data: Int = 0
var body: some View {
Text("\(data)")
Button(action: update) {
Text("update") // works as expected
}
}
func update() {
// fetch data from external source
data = 42
}
}
struct MainView: View {
var child = ChildView()
var body: some View {
VStack {
child
Button(action: {
child.update()
}) {
Text("update") // In fact calls the function, but doesn't set the data variable to the new value
}
}
}
}
When googling for a solution, I only came across people suggesting to move update and data to MainView and then pass a binding of data to ChildView.
However, following this logic I'd have to blow up MainView by adding all the data access logic in there. My point of having ChildView at all is to break up code into smaller chunks and to reuse ChildView including the data access methods in other parent views, too.
I just cannot believe there's no way of doing this in SwiftUI.
Is completely understandable to be confused at first with how to deal with state on SwiftUI, but hang on there, you will find your way soon enough.
What you want to do can be achieved in many different ways, depending on the requirements and limitations of your project.
I will mention a few options, but I'm sure there are more, and all of them have pros and cons, but hopefully one can suit your needs.
Binding
Probably the easiest would be to use a #Binding, here a good tutorial/explanation of it.
An example would be to have data declared on your MainView and pass it as a #Binding to your ChildView. When you need to change the data, you change it directly on the MainView and will be reflected on both.
This solutions leads to having the logic on both parts, probably not ideal, but is up to what you need.
Also notice how the initialiser for ChildView is directly on the body of MainView now.
Example
struct ChildView: View {
#Binding var data: Int
var body: some View {
Text("\(data)")
Button(action: update) {
Text("update") // works as expected
}
}
func update() {
// fetch data from external source
data = 42
}
}
struct MainView: View {
#State var data: Int = 0
var body: some View {
VStack {
ChildView(data: $data)
Button(action: {
data = 42
}) {
Text("update") // In fact calls the function, but doesn't set the data variable to the new value
}
}
}
}
ObservableObject
Another alternative would be to remove state and logic from your views, using an ObservableObject, here an explanation of it.
Example
class ViewModel: ObservableObject {
#Published var data: Int = 0
func update() {
// fetch data from external source
data = 42
}
}
struct ChildView: View {
#ObservedObject var viewModel: ViewModel
var body: some View {
Text("\(viewModel.data)")
Button(action: viewModel.update) {
Text("update") // works as expected
}
}
}
struct MainView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
VStack {
ChildView(viewModel: viewModel)
Button(action: {
viewModel.update()
}) {
Text("update") // In fact calls the function, but doesn't set the data variable to the new value
}
}
}
}

MVVM model in SwiftUI

I want to separate view from view model according to MVVM. How would I create a model in SwiftUI? I read that one should use struct rather than class.
As an example I have a model for a park where you can plant trees in:
// View Model
struct Park {
var numberOfTrees = 0
func plantTree() {
numberOfTrees += 1 // Cannot assign to property: 'self' is immutable
}
}
// View
struct ParkView: View {
var park: Park
var body: some View {
// …
}
}
Read things about #State in such things, that make structs somewhat mutable, so I tried:
struct Park {
#State var numberOfTrees = 0 // Enum 'State' cannot be used as an attribute
func plantTree() {
numberOfTrees += 1 // Cannot assign to property: 'self' is immutable
}
}
I did use #State successfully directly in a View. This doesn’t help with separating the view model code though.
I could use class:
class Park: ObservableObject {
var numberOfTrees = 0
func plantTree() {
numberOfTrees += 1
}
}
…but then I would have trouble using this view model nested in another one, say City:
struct City {
#ObservedObject var centerPark: Park
}
Changes in centerPark wouldn’t be published as Park now is reference type (at least not in my tests or here). Also, I would like to know how you solve this using a struct.
as a starting point:
// Model
struct Park {
var numberOfTrees = 0
mutating func plantTree() { // `mutating`gets rid of your error
numberOfTrees += 1
}
}
// View Model
class CityVM: ObservableObject {
#Published var park = Park() // creates a Park and publishes it to the views
// ... other #Published things ...
// Intents:
func plantTree() {
park.plantTree()
}
}
// View
struct ParkView: View {
// create the ViewModel, which creates the model(s)
// usually you would do this in the App struct and make available to all views by .environmentObject
#StateObject var city = CityVM()
var body: some View {
VStack {
Text("My city has \(city.park.numberOfTrees) trees.")
Button("Plant one more") {
city.plantTree()
}
}
}
}
mutating func is the fix but I thought I'd include some other info below:
We don't use MVVM with SwiftUI because we don't use classes for transient view state and we don't control the View in the MVVM/MVC sense. SwiftUI creates and updates the real view objects automatically for us, i.e. UILabels, UITableView etc. The SwiftUI View structs are essentially the view model already, so if you were to recreate that as an object not only will you be needlessly make your code more complex but also would introduce object reference bugs SwiftUI is trying to eliminate by using structs. With property wrappers like #State and #Binding SwiftUI is doing some magic to make the struct behave like an object it is not a good idea to ignore that. To make your View structs more testable you can extract related vars into a struct and use mutating funcs like this:
// View Model
struct ParkConfig {
var numberOfTrees = 0
mutating func plantTree() {
numberOfTrees += 1
}
}
struct ContentView {
#State var parkConfig = ParkConfig()
var body: some View {
ParkView(config: $parkConfig)
}
}
// View
struct ParkView: View {
#Binding var config: ParkConfig
var body: some View {
Button("Click Me") {
config.plantTree()
}
}
}
You can see Apple demonstrate this pattern in Data Essentials in SwiftUI WWDC 2020 at 4:18 where he says "EditorConfig can maintain invariants on its properties and be tested independently. And because EditorConfig is a value type, any change to a property of EditorConfig, like its progress, is visible as a change to EditorConfig itself."

SwiftUI - #Binding to a computed property which accesses value inside ObservableObject property duplicates the variable?

In the code below (a stripped-down version of some code in a project) I'm using a MVVM pattern with two views:
ViewA - displays a value stored in an ObservableObject ViewModel;
ViewB - displays the same value and has a Slider that changes that value, which is passed to the view using Binding.
Inside of ViewModelA I have a computed property which serves both to avoid the View from accessing the Model directly and to perform some other operations when the value inside the model (the one being displayed) is changed.
I'm also passing that computed value to a ViewModelB, using Binding, which acts as a StateObject for ViewB. However, when dragging the Slider to change that value, the value changes on ViewA but doesn't change on ViewB and the slider itself doesn't slide. As expected, when debugging, the wrappedValue inside the Binding is not changing. But how is the change propagated upwards (through the Binding's setters, I imagine) but not downwards back to ViewB?? I imagine this can only happen if the variable is being duplicated somewhere and changed only in one place, but I can't seem to understand where or if that's what's actually happening.
Thanks in advance!
Views:
import SwiftUI
struct ContentView: View {
#StateObject var viewModelA = ViewModelA()
var body: some View {
VStack{
ViewA(value: viewModelA.value)
ViewB(value: $viewModelA.value)
}
}
}
struct ViewA: View {
let value: Double
var body: some View {
Text("\(value)").padding()
}
}
struct ViewB: View {
#StateObject var viewModelB: ViewModelB
init(value: Binding<Double>){
_viewModelB = StateObject(wrappedValue: ViewModelB(value: value))
}
var body: some View {
VStack{
Text("\(viewModelB.value)")
Slider(value: $viewModelB.value, in: 0...1)
}
}
}
ViewModels:
class ViewModelA: ObservableObject {
#Published var model = Model()
var value: Double {
get {
model.value
}
set {
model.value = newValue
// perform other checks and operations
}
}
}
class ViewModelB: ObservableObject {
#Binding var value: Double
init(value: Binding<Double>){
self._value = value
}
}
Model:
struct Model {
var value: Double = 0
}
If you only look where you can't go, you might just miss the riches below
Breaking single source of truth, and breaching local (private) property of #StateObjectby sharing it via Binding are two places where you can't go.
#EnvironmentObject or more generally the concept of "shared object" between views are the riches below.
This is an example of doing it without MVVM nonsense:
import SwiftUI
final class EnvState: ObservableObject {#Published var value: Double = 0 }
struct ContentView: View {
#EnvironmentObject var eos: EnvState
var body: some View {
VStack{
ViewA()
ViewB()
}
}
}
struct ViewA: View {
#EnvironmentObject var eos: EnvState
var body: some View {
Text("\(eos.value)").padding()
}
}
struct ViewB: View {
#EnvironmentObject var eos: EnvState
var body: some View {
VStack{
Text("\(eos.value)")
Slider(value: $eos.value, in: 0...1)
}
}
}
Isn't this easier to read, cleaner, less error-prone, with fewer overheads, and without serious violation of fundamental coding principles?
MVVM does not take value type into consideration. And the reason Swift introduces value type is so that you don't pass shared mutable references and create all kinds of bugs.
Yet the first thing MVVM devs do is to introduce shared mutable references for every view and pass references around via binding...
Now to your question:
the only options I see are either using only one ViewModel per Model, or having to pass the Model (or it's properties) between ViewModels through Binding
Another option is to drop MVVM, get rid of all view models, and use #EnvironmentObject instead.
Or if you don't want to drop MVVM, pass #ObservedObject (your view model being a reference type) instead of #Binding.
E.g.;
struct ContentView: View {
#ObservedObject var viewModelA = ViewModelA()
var body: some View {
VStack{
ViewA(value: viewModelA)
ViewB(value: viewModelA)
}
}
}
On a side note, what's the point of "don't access model directly from view"?
It makes zero sense when your model is value type.
Especially when you pass view model reference around like cookies in a party so everyone can have it.
Really it looks like broken single-source or truth concept. Instead the following just works (ViewModelB might probably be needed for something, but not for this case)
Tested with Xcode 12 / iOS 14
Only modified parts:
struct ContentView: View {
#StateObject var viewModelA = ViewModelA()
var body: some View {
VStack{
ViewA(value: viewModelA.value)
ViewB(value: $viewModelA.model.value)
}
}
}
struct ViewB: View {
#Binding var value: Double
var body: some View {
VStack{
Text("\(value)")
Slider(value: $value, in: 0...1)
}
}
}

How do you edit the members of a Struct of type View from another Struct of type View? (SwiftUI)

I have the following 2 structs within separate files and displayed in the contentView. What I'm trying to understand is how to maintain the contentView as only displaying and organizing the UI. Placing all of my other views in separate files. My first thought was the correct approach would be to use static variables updated by functions that are called from the button press action. But the buttons text did not update accordingly. As they are dynamically updated according to #State.
update:
I attempted to solve this by using protocols and delegates to no avail. By my understanding this delegate call should be receiving on the other end and updating structcop.ID and the change should be reflected in the content view.
FILE 1
import SwiftUI
struct structdispatch: View {
var radio:RadioDelegate?
func send() {
radio?.update()
self.debug()
}
var body: some View {
Button(action: self.send)
{Text("DISPATCHER")}
}
func debug() {
print("Button is sending?")
}
}
struct structdispatch_Previews: PreviewProvider {
static var previews: some View {
structdispatch()
}
}
**FILE 2:**
import SwiftUI
protocol RadioDelegate {
func update()
}
struct structcop: View, RadioDelegate {
#State public var ID:Int = 3
func update(){
print("message recieved")
self.ID += 1
print(self.ID)
}
var body: some View {
Text(String(self.ID))
}
}
struct structcop_Previews: PreviewProvider {
static var previews: some View {
structcop()
}
}
DEBUG CONSOLE RETURNS:
The Button is working
View is updated on some internal DynamicProperty change, like #State, so here is possible solution
Tested with Xcode 12 / iOS 14
struct structcop: View {
static public var ID = 3
#State private var localID = Self.ID {
didSet {
Self.ID = localID
}
}
var body: some View {
Button(action: printme)
{Text(String(localID))}
}
func printme(){
self.localID = 5
print(structcop.ID)
}
}
Solution:
After some digging I have a working solution but I'm still curious if there is a way to modify properties of other structs while maintaining dynamic view updates.
Solution: store data for display in an observable object which will either read or act as the model which the user is interacting with.
An observable object is a custom object for your data that can be bound to a view from storage in SwiftUI’s environment. SwiftUI watches for any changes to observable objects that could affect a view, and displays the correct version of the view after a change. -apple
A new model type is declared that conforms to the ObservableObject protocol from the Combine framework. SwiftUI subscribes to the observable object and updates relevant views that need refreshing when the data changes. SceneDelegate.swift needs to have the .environmentObject(_:) modifier added to your root view.
Properties declared within the ObservableObject should be set to #Published so that any changes are picked up by subscribers.
For test code I created an ObservableObject called headquarters
import SwiftUI
import Combine
final class hq: ObservableObject {
#Published var info = headQuarters
}
let headQuarters = hqData(id: 3)
struct hqData {
var id: Int
mutating func bump() {
self.id += 1
}
}
In my struct dispatch I subscribed to the object and called a function that iterated the id in the model whenever the button was pressed. My struct cop also subscribed to the object and thus the model and button text updated accordingly to changes.
struct dispatch: View {
#EnvironmentObject private var hq: headqarters
var body: some View {
Button(action: {self.hq.info.bump()}) {
Text("Button")
}
}
}
struct cop: View {
#EnvironmentObject private var hq: headquarters
var body: some View {
Text(String(self.hq.info.id))
}
}

SwiftUI: ObservableObject does not persist its State over being redrawn

Problem
In Order to achieve a clean look and feel of the App's code, I create ViewModels for every View that contains logic.
A normal ViewModel looks a bit like this:
class SomeViewModel: ObservableObject {
#Published var state = 1
// Logic and calls of Business Logic goes here
}
and is used like so:
struct SomeView: View {
#ObservedObject var viewModel = SomeViewModel()
var body: some View {
// Code to read and write the State goes here
}
}
This workes fine when the Views Parent is not being updated. If the parent's state changes, this View gets redrawn (pretty normal in a declarative Framework). But also the ViewModel gets recreated and does not hold the State afterward. This is unusual when you compare to other Frameworks (eg: Flutter).
In my opinion, the ViewModel should stay, or the State should persist.
If I replace the ViewModel with a #State Property and use the int (in this example) directly it stays persisted and does not get recreated:
struct SomeView: View {
#State var state = 1
var body: some View {
// Code to read and write the State goes here
}
}
This does obviously not work for more complex States. And if I set a class for #State (like the ViewModel) more and more Things are not working as expected.
Question
Is there a way of not recreating the ViewModel every time?
Is there a way of replicating the #State Propertywrapper for #ObservedObject?
Why is #State keeping the State over the redraw?
I know that usually, it is bad practice to create a ViewModel in an inner View but this behavior can be replicated by using a NavigationLink or Sheet.
Sometimes it is then just not useful to keep the State in the ParentsViewModel and work with bindings when you think of a very complex TableView, where the Cells themself contain a lot of logic.
There is always a workaround for individual cases, but I think it would be way easier if the ViewModel would not be recreated.
Duplicate Question
I know there are a lot of questions out there talking about this issue, all talking about very specific use-cases. Here I want to talk about the general problem, without going too deep into custom solutions.
Edit (adding more detailed Example)
When having a State-changing ParentView, like a list coming from a Database, API, or cache (think about something simple). Via a NavigationLink you might reach a Detail-Page where you can modify the Data. By changing the data the reactive/declarative Pattern would tell us to also update the ListView, which would then "redraw" the NavigationLink, which would then lead to a recreation of the ViewModel.
I know I could store the ViewModel in the ParentView / ParentView's ViewModel, but this is the wrong way of doing it IMO. And since subscriptions are destroyed and/or recreated - there might be some side effects.
Finally, there is a Solution provided by Apple: #StateObject.
By replacing #ObservedObject with #StateObject everything mentioned in my initial post is working.
Unfortunately, this is only available in ios 14+.
This is my Code from Xcode 12 Beta (Published June 23, 2020)
struct ContentView: View {
#State var title = 0
var body: some View {
NavigationView {
VStack {
Button("Test") {
self.title = Int.random(in: 0...1000)
}
TestView1()
TestView2()
}
.navigationTitle("\(self.title)")
}
}
}
struct TestView1: View {
#ObservedObject var model = ViewModel()
var body: some View {
VStack {
Button("Test1: \(self.model.title)") {
self.model.title += 1
}
}
}
}
class ViewModel: ObservableObject {
#Published var title = 0
}
struct TestView2: View {
#StateObject var model = ViewModel()
var body: some View {
VStack {
Button("StateObject: \(self.model.title)") {
self.model.title += 1
}
}
}
}
As you can see, the StateObject Keeps it value upon the redraw of the Parent View, while the ObservedObject is being reset.
I agree with you, I think this is one of many major problems with SwiftUI. Here's what I find myself doing, as gross as it is.
struct MyView: View {
#State var viewModel = MyViewModel()
var body : some View {
MyViewImpl(viewModel: viewModel)
}
}
fileprivate MyViewImpl : View {
#ObservedObject var viewModel : MyViewModel
var body : some View {
...
}
}
You can either construct the view model in place or pass it in, and it gets you a view that will maintain your ObservableObject across reconstruction.
Is there a way of not recreating the ViewModel every time?
Yes, keep ViewModel instance outside of SomeView and inject via constructor
struct SomeView: View {
#ObservedObject var viewModel: SomeViewModel // << only declaration
Is there a way of replicating the #State Propertywrapper for #ObservedObject?
No needs. #ObservedObject is-a already DynamicProperty similarly to #State
Why is #State keeping the State over the redraw?
Because it keeps its storage, ie. wrapped value, outside of view. (so, see first above again)
You need to provide custom PassThroughSubject in your ObservableObject class. Look at this code:
//
// Created by Франчук Андрей on 08.05.2020.
// Copyright © 2020 Франчук Андрей. All rights reserved.
//
import SwiftUI
import Combine
struct TextChanger{
var textChanged = PassthroughSubject<String,Never>()
public func changeText(newValue: String){
textChanged.send(newValue)
}
}
class ComplexState: ObservableObject{
var objectWillChange = ObservableObjectPublisher()
let textChangeListener = TextChanger()
var text: String = ""
{
willSet{
objectWillChange.send()
self.textChangeListener.changeText(newValue: newValue)
}
}
}
struct CustomState: View {
#State private var text: String = ""
let textChangeListener: TextChanger
init(textChangeListener: TextChanger){
self.textChangeListener = textChangeListener
print("did init")
}
var body: some View {
Text(text)
.onReceive(textChangeListener.textChanged){newValue in
self.text = newValue
}
}
}
struct CustomStateContainer: View {
//#ObservedObject var state = ComplexState()
var state = ComplexState()
var body: some View {
VStack{
HStack{
Text("custom state View: ")
CustomState(textChangeListener: state.textChangeListener)
}
HStack{
Text("ordinary Text View: ")
Text(state.text)
}
HStack{
Text("text input: ")
TextInput().environmentObject(state)
}
}
}
}
struct TextInput: View {
#EnvironmentObject var state: ComplexState
var body: some View {
TextField("input", text: $state.text)
}
}
struct CustomState_Previews: PreviewProvider {
static var previews: some View {
return CustomStateContainer()
}
}
First, I using TextChanger to pass new value of .text to .onReceive(...) in CustomState View. Note, that onReceive in this case gets PassthroughSubject, not the ObservableObjectPublisher. In last case you will have only Publisher.Output in perform: closure, not the NewValue. state.text in that case would have old value.
Second, look at the ComplexState class. I made an objectWillChange property to make text changes send notification to subscribers manually. Its almost the same like #Published wrapper do. But, when the text changing it will send both, and objectWillChange.send() and textChanged.send(newValue). This makes you be able to choose in exact View, how to react on state changing. If you want ordinary behavior, just put the state into #ObservedObject wrapper in CustomStateContainer View. Then, you will have all the views recreated and this section will get updated values too:
HStack{
Text("ordinary Text View: ")
Text(state.text)
}
If you don't want all of them to be recreated, just remove #ObservedObject. Ordinary text View will stop updating, but CustomState will. With no recreating.
update:
If you want more control, you can decide while changing the value, who do you want to inform about that change.
Check more complex code:
//
//
// Created by Франчук Андрей on 08.05.2020.
// Copyright © 2020 Франчук Андрей. All rights reserved.
//
import SwiftUI
import Combine
struct TextChanger{
// var objectWillChange: ObservableObjectPublisher
// #Published
var textChanged = PassthroughSubject<String,Never>()
public func changeText(newValue: String){
textChanged.send(newValue)
}
}
class ComplexState: ObservableObject{
var onlyPassthroughSend = false
var objectWillChange = ObservableObjectPublisher()
let textChangeListener = TextChanger()
var text: String = ""
{
willSet{
if !onlyPassthroughSend{
objectWillChange.send()
}
self.textChangeListener.changeText(newValue: newValue)
}
}
}
struct CustomState: View {
#State private var text: String = ""
let textChangeListener: TextChanger
init(textChangeListener: TextChanger){
self.textChangeListener = textChangeListener
print("did init")
}
var body: some View {
Text(text)
.onReceive(textChangeListener.textChanged){newValue in
self.text = newValue
}
}
}
struct CustomStateContainer: View {
//var state = ComplexState()
#ObservedObject var state = ComplexState()
var body: some View {
VStack{
HStack{
Text("custom state View: ")
CustomState(textChangeListener: state.textChangeListener)
}
HStack{
Text("ordinary Text View: ")
Text(state.text)
}
HStack{
Text("text input with full state update: ")
TextInput().environmentObject(state)
}
HStack{
Text("text input with no full state update: ")
TextInputNoUpdate().environmentObject(state)
}
}
}
}
struct TextInputNoUpdate: View {
#EnvironmentObject var state: ComplexState
var body: some View {
TextField("input", text: Binding( get: {self.state.text},
set: {newValue in
self.state.onlyPassthroughSend.toggle()
self.state.text = newValue
self.state.onlyPassthroughSend.toggle()
}
))
}
}
struct TextInput: View {
#State private var text: String = ""
#EnvironmentObject var state: ComplexState
var body: some View {
TextField("input", text: Binding(
get: {self.text},
set: {newValue in
self.state.text = newValue
// self.text = newValue
}
))
.onAppear(){
self.text = self.state.text
}.onReceive(state.textChangeListener.textChanged){newValue in
self.text = newValue
}
}
}
struct CustomState_Previews: PreviewProvider {
static var previews: some View {
return CustomStateContainer()
}
}
I made a manual Binding to stop broadcasting objectWillChange. But you still need to gets new value in all the places you changing this value to stay synchronized. Thats why I modified TextInput too.
Is that what you needed?
My solution is use EnvironmentObject and don't use ObservedObject at view it's viewModel will be reset, you pass through hierarchy by
.environmentObject(viewModel)
Just init viewModel somewhere it will not be reset(example root view).