I have a ObservableObject class called MyObjectModel that is passed to a struct like this:
var body: some View {
MyView(myObjectModel)
But on another context I do not have a model to pass, so I want to call MyView simply as
var body: some View {
MyView()
So I thought I could initialize MyView like
struct MyView: View {
#ObservedObject private var model: MyObjectModel?
init(model: MyObjectModel? = nil) {
self.model = model
}
But Xcode will not let me use #ObservedObject on an optional.
How do I do that?
The ObservedObject wrapper does not have constructor with optional for now (and we cannot extend Optional with conformance to ObservableObject, because it is not a class).
A possible approach is to have some specific mark that there is no model, as it would be nil.
Here is a demo:
class MyObjectModel: ObservableObject {
static let None = MyObjectModel() // Like NSNull.null
}
struct MyView: View {
#ObservedObject private var model: MyObjectModel
init(model: MyObjectModel? = nil) {
self.model = model ?? MyObjectModel.None
}
var body: some View {
if self.model === MyObjectModel.None {
Text("Same as it would be nil!") // << here !!
} else {
Text("For real model")
}
}
}
Related
How to observe property value in SwiftUI.
I know some basic publisher and observer patterns. But here is a scenario i am not able to implement.
class ScanedDevice: NSObject, Identifiable {
//some variables
var currentStatusText: String = "Pending"
}
here CurrentStatusText is changed by some other callback method that update the status.
Here there is Model class i am using
class SampleModel: ObservableObject{
#Published var devicesToUpdated : [ScanedDevice] = []
}
swiftui component:
struct ReviewView: View {
#ObservedObject var model: SampleModel
var body: some View {
ForEach(model.devicesToUpdated){ device in
Text(device.currentStatusText)
}
}
}
Here in UI I want to see the real-time status
I tried using publisher inside ScanDevice class but sure can to use it in 2 layer
You can observe your class ScanedDevice, however you need to manually use a objectWillChange.send(),
to action the observable change, as shown in this example code.
class ScanedDevice: NSObject, Identifiable {
var name: String = "some name"
var currentStatusText: String = "Pending"
init(name: String) {
self.name = name
}
}
class SampleViewModel: ObservableObject{
#Published var devicesToUpdated: [ScanedDevice] = []
}
struct ReviewView: View {
#ObservedObject var viewmodel: SampleViewModel
var body: some View {
VStack (spacing: 33) {
ForEach(viewmodel.devicesToUpdated){ device in
HStack {
Text(device.name)
Text(device.currentStatusText).foregroundColor(.red)
}
Button("Change \(device.name)") {
viewmodel.objectWillChange.send() // <--- here
device.currentStatusText = UUID().uuidString
}.buttonStyle(.bordered)
}
}
}
}
struct ContentView: View {
#StateObject var viewmodel = SampleViewModel()
var body: some View {
ReviewView(viewmodel: viewmodel)
.onAppear {
viewmodel.devicesToUpdated = [ScanedDevice(name: "device-1"), ScanedDevice(name: "device-2")]
}
}
}
I have a question regarding the combination of SwiftUI and MVVM.
Before we start, I have read some posts discussing whether the combination of SwiftUI and MVVM is necessary. But I don't want to discuss this here, as it has been covered elsewhere. I just want to know if it is possible and, if yes, how. :)
So here comes the code. I tried to add the ViewModel Layer in between the updated Object class that contains a number that should be updated when a button is pressed. The problem is that as soon as I put the ViewModel Layer in between, the UI does not automatically update when the button is pressed.
View:
struct ContentView: View {
#ObservedObject var viewModel = ViewModel()
#ObservedObject var numberStorage = NumberStorage()
var body: some View {
VStack {
// Text("\(viewModel.getNumberObject().number)")
// .padding()
// Button("IncreaseNumber") {
// viewModel.increaseNumber()
// }
Text("\(numberStorage.getNumberObject().number)")
.padding()
Button("IncreaseNumber") {
numberStorage.increaseNumber()
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
ViewModel:
class ViewModel: ObservableObject {
#Published var number: NumberStorage
init() {
self.number = NumberStorage()
}
func increaseNumber() {
self.number.increaseNumber()
}
func getNumberObject() -> NumberObject {
self.number.getNumberObject()
}
}
Model:
class NumberStorage:ObservableObject {
#Published var numberObject: NumberObject
init() {
numberObject = NumberObject()
}
public func getNumberObject() -> NumberObject {
return self.numberObject
}
public func increaseNumber() {
self.numberObject.number+=1
}
}
struct NumberObject: Identifiable {
let id = UUID()
var number = 0
} ```
Looking forward to your feedback!
I think your code is breaking MVVM, as you're exposing to the view a storage model. In MVVM, your ViewModel should hold only two things:
Values that your view should display. These values should be automatically updated using a binding system (in your case, Combine)
Events that the view may produce (in your case, a button tap)
Having that in mind, your ViewModel should wrap, adapt and encapsulate your model. We don't want model changes to affect the view. This is a clean approach that does that:
View:
struct ContentView: View {
#StateObject // When the view creates the object, it must be a state object, or else it'll be recreated every time the view is recreated
private var viewModel = ViewModel()
var body: some View {
VStack {
Text("\(viewModel.currentNumber)") // We don't want to use functions here, as that will create a new object , as SwiftUI needs the same reference in order to keep track of changes
.padding()
Button("IncreaseNumber") {
viewModel.increaseNumber()
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
ViewModel:
class ViewModel: ObservableObject {
#Published
private(set) var currentNumber: Int = 0 // Private set indicates this should only be mutated by the viewmodel
private let numberStorage = NumberStorage()
init() {
numberStorage.currentNumber
.map { $0.number }
.assign(to: &$currentNumber) // Here we're binding the current number on the storage to the published var that the view is listening to.`&$` basically assigns it to the publishers address
}
func increaseNumber() {
self.numberStorage.increaseNumber()
}
}
Model:
class NumberStorage {
private let currentNumberSubject = CurrentValueSubject<NumberObject, Never>(NumberObject())
var currentNumber: AnyPublisher<NumberObject, Never> {
currentNumberSubject.eraseToAnyPublisher()
}
func increaseNumber() {
let currentNumber = currentNumberSubject.value.number
currentNumberSubject.send(.init(number: currentNumber + 1))
}
}
struct NumberObject: Identifiable { // I'd not use this, just send and int directly
let id = UUID()
var number = 0
}
It's a known problem. Nested observable objects are not supported yet in SwiftUI. I don't think you need ViewModel+Model here since ViewModel seems to be enough.
To make this work you have to trigger objectWillChange of your viewModel manually when objectWillChange of your model is triggered:
class ViewModel: ObservableObject {
init() {
number.objectWillChange.sink { [weak self] (_) in
self?.objectWillChange.send()
}.store(in: &cancellables)
}
}
You better listen to only the object you care not the whole observable class if it is not needed.
Plus:
Since instead of injecting, you initialize your viewModel in your view, you better use StateObject instead of ObservedObject. See the reference from Apple docs: Managing model data in your app
One way you could handle this is to observe the publishers in your Storage class and send the objectWillChange publisher when it changes. I have done this in personal projects by adding a class that all my view models inherit from which provides a nice interface and handles the Combine stuff like this:
Parent ViewModel
import Combine
class ViewModel: ObservableObject {
private var cancellables: Set<AnyCancellable> = []
func publish<T>(on publisher: Published<T>.Publisher) {
publisher.sink { [weak self] _ in self?.objectWillChange.send() }
.store(in: &cancellables)
}
}
Specific ViewModel
class ContentViewModel: ViewModel {
private let numberStorage = NumberStorage()
var number: Int { numberStorage.numberObject.number }
override init() {
super.init()
publish(on: numberStorage.$numberObject)
}
func increaseNumber() {
numberStorage.increaseNumber()
}
}
View
struct ContentView: View {
#StateObject var viewModel = ContentViewModel()
var body: some View {
VStack {
Text("\(viewModel.number)")
.padding()
Button("IncreaseNumber") {
viewModel.increaseNumber()
}
}
}
}
Model/Storage
class NumberStorage:ObservableObject {
#Published var numberObject: NumberObject
init() {
numberObject = NumberObject()
}
public func increaseNumber() {
self.numberObject.number += 1
}
}
struct NumberObject: Identifiable {
let id = UUID()
var number = 0
}
This results in the view re-rendering any time Storage.numberObject changes.
I'm trying to implement my app architecture loading in the app struct an object containing the data to be shared in all the views of the app through an environment object:
#main
struct SMT_testingApp: App {
#StateObject private var dataManager = DataManager()
var body: some Scene {
WindowGroup {
ContentView()
.environmentObject(dataManager)
}
}
}
Here's the Datamanager class publishing the var containing the data:
class DataManager: ObservableObject {
#Published var SMTItemList: [SMTItem] = [SMTItem(id: UUID(), itemDesc: "", itemCreaDate: Date(), itemUpdDate: Date(), itemTags: [], linkedItemsUID: [])]
var urlFile: URL {
getDocumentsDirectory().appendingPathComponent("/SMT.json")
}
init() { loadData() }
func getDocumentsDirectory() -> URL {
let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
return paths[0]
}
func loadData() {
//...
After here the View that contain the instance of his view model:
struct ContentView: View {
#StateObject private var viewModel = ViewModel()
var body: some View {
List(viewModel.dataManager.SMTItemList) { item in
SMTItemView(item: item)
}
}
}
struct SMTItemView: View {
var item : SMTItem
var body: some View {
Text("Item desc: \(item.itemDesc)")
}
}
And finally, the view model that contains the environment object with the data.
extension ContentView {
class ViewModel: ObservableObject{
#EnvironmentObject var dataManager: DataManager
}
}
Now, the code is built correctly but at runtime I obtain this error in the content View:
What I'm doing wrong? Is correct implementing an architecture that way (one enviroment object with the data and many views/view models) ?
Thanks
#EnvironmentObject must be in view scope, not view model class. Like
struct ContentView: View {
#StateObject private var viewModel = ViewModel()
#EnvironmentObject var dataManager: DataManager // << here !!
var body: some View {
List(dataManager.SMTItemList) { item in
SMTItemView(item: item)
}
}
}
I have a ObservableObject-Class which inside this class, I got a published var with name of persones! I do initialize it with some data called: allData.
Then I try to update my allData with action of a Button, and this action apply the wanted update to my allData, but my published var has no idea, that this data got updated!
How we can make published see the new updated allData?
struct PersonData: Identifiable {
let id = UUID()
var name: String
}
var allData = [PersonData(name: "Bob"), PersonData(name: "Nik"), PersonData(name: "Tak"), PersonData(name: "Sed"), PersonData(name: "Ted")]
class PersonDataModel: ObservableObject {
#Published var persones: [PersonData] = allData
}
struct ContentView: View {
#StateObject var personDataModel = PersonDataModel()
var body: some View {
VStack
{
Button("update allData") { allData = [PersonData(name: "Bob")] }
HStack
{
ForEach(personDataModel.persones) { person in Text(person.name) }
}
}
.font(Font.title)
}
}
PS: I don´t want use .onChange or other things for this, I would like this happens internally in my class.
Also I know I can use down code for this work, but that is not the answer
personDataModel.persones = [PersonData(name: "Bob")]
Having a top-level property (outside of any class or struct) is probably not a good idea. I don't see the whole picture, but it looks like your app needs a global state (e.g., a #StateObject initialised on the App level). Consider this answer:
Add EnvironmentObject in SwiftUI 2.0
If you really need to observe your array, you need to make it observable.
One option is to use CurrentValueSubject from the Combine framework:
var persons = ["Bob", "Nik", "Tak", "Sed", "Ted"].map(PersonData.init)
var allData = CurrentValueSubject<[PersonData], Never>(persons)
class PersonDataModel: ObservableObject {
#Published var persones: [PersonData] = allData.value
private var cancellables = Set<AnyCancellable>()
init() {
allData
.sink { [weak self] in
self?.persones = $0
}
.store(in: &cancellables)
}
}
struct ContentView: View {
#StateObject var personDataModel = PersonDataModel()
var body: some View {
VStack {
Button("update allData") {
allData.send([PersonData(name: "Bob")])
}
HStack {
ForEach(personDataModel.persones) { person in
Text(person.name)
}
}
}
.font(Font.title)
}
}
The allData is copied into persones at initialization time, so changing it afterwards does nothing to personDataModel. After StateObject created you have to work with it, like
Button("update allData") {
self.personDataModel.persones = [PersonData(name: "Bob")]
}
I think you're doing something wrong.
if you want to update all your views, you have to pass the same object with #EnviromentObject.
I don't know your storage method (JSON, CORE DATA, iCloud) but the correct approach is to update directly the model
class PersonDataModel: ObservableObject
{
#Published var persones: [PersonData] = loadFromJSON //one func that is loading your object stored as JSON file
func updateAllData() {
storeToJSON(persones) //one func that is storing your object as JSON file
}
}
struct ContentView: View {
#StateObject var personDataModel = PersonDataModel()
var body: some View {
VStack
{
Button("update allData") {
self.personDataModel.persones = [PersonData(name: "Bob")]
}
HStack
{
ForEach(personDataModel.persones) { person in Text(person.name) }
}
}
.font(Font.title)
.onChange($personDataModel.persones) {
persones.updateAllData()
}
}
}
Let's assume a model, which implements the protocol ObservableObject and has got a #Published property name.
// MARK: Model
class ContentSinglePropertyModel: ObservableObject {
#Published public var name: String
}
Now, I would like to display that name in a view and update the view, whenever name in the model changes. Additionally, I would like to use the Model-View-ViewModel (MVVM) pattern to achieve this goal.
// MARK: ViewModel
final class ContentSinglePropertyViewModel: ObservableObject {
private let model: ContentSinglePropertyModel
#Published var name: String = ""
init() {
self.model = ContentSinglePropertyModel()
}
}
// MARK: View
struct ContentSinglePropertyView: View {
#ObservedObject var viewModel: ContentSinglePropertyViewModel
var body: some View {
Text(self.viewModel.name)
}
}
Since I don't like the idea to make the model or it's properties public within the viewmodel, one option is to wrap the model's property name in the viewmodel. My question is: How to connect the name of the model and the viewmodel in the most idiomatic way?
I've came up with the solution to update the viewmodel's property through the use of Combine's assign method:
self.model.$name.assign(to: \.name, on: self).store(in: &self.cancellables)
Is there a better solution?
My working example:
import SwiftUI
import Combine
// MARK: Model
class ContentSinglePropertyModel: ObservableObject {
#Published public var name: String
init() {
self.name = "Initial value"
}
func doSomething() {
self.name = "Changed value"
}
}
// MARK: ViewModel
final class ContentSinglePropertyViewModel: ObservableObject {
private let model: ContentSinglePropertyModel
private var cancellables: Set<AnyCancellable> = []
#Published var name: String = ""
init() {
self.model = ContentSinglePropertyModel()
// glue Model and ViewModel
self.model.$name.assign(to: \.name, on: self).store(in: &self.cancellables)
}
func doSomething() {
self.model.doSomething()
}
}
// MARK: View
struct ContentSinglePropertyView: View {
#ObservedObject var viewModel: ContentSinglePropertyViewModel
var body: some View {
VStack {
Text(self.viewModel.name)
Button("Do something!", action: {
self.viewModel.doSomething()
})
}
}
}
struct ContentSinglePropertyView_Previews: PreviewProvider {
static var previews: some View {
ContentSinglePropertyView(viewModel: .init())
}
}