So I'm very familiar with UIKit but just recently started working with SwiftUI. I have this very basic view coming from a NavigationLink and I can't figure out why this code does not work. I can't update that #State var`, I tried everything you can't think of. Am I doing something wrong here? Thanks!
struct Test: View {
#State private var settingsEnabled: Bool = false {
didSet {
print(oldValue)
print("DID SET")
print(settingsEnabled)
}
}
var body: some View {
Button(action: {
self.settingsEnabled.toggle()
}) {
Text(String("\(self.settingsEnabled)"))
}
}
}
You seem to be missing the View conformance.
struct Test: View {
...
}
Update: The seems to have occurred because you were using the body of the Test struct directly instead of the Test struct that conforms to View protocol, which in-turn contains the settingsEnabled #State variable.
Related
I have a custom ViewModifier which simply returns the same content attached with a onReceive modifier, the onReceive is not triggered, here is a sample code that you can copy, paste and run in XCode:
import SwiftUI
import Combine
class MyViewModel: ObservableObject {
#Published var myProperty: Bool = false
}
struct ContentView: View {
#ObservedObject var viewModel: MyViewModel
var body: some View {
Text("Hello, World!")
.modifier(MyOnReceive(viewModel: viewModel))
.onTapGesture {
self.viewModel.myProperty = true
}
}
}
struct MyOnReceive: ViewModifier {
#ObservedObject var viewModel: MyViewModel
func body(content: Content) -> some View {
content
.onReceive(viewModel.$myProperty) { theValue in
print("The Value is \(theValue)") // <--- this is not executed
}
}
}
is SwiftUI designed to disallow onReceive to execute inside a ViewModifier or is it a bug ? I have a view in my real life project that gets bigger with some business logic put inside onReceive, so I need to clean that view by separating it from onReceive.
ok, this works for me:
func body(content: Content) -> some View {
content
.onAppear() // <--- this makes it work
.onReceive(viewModel.$myProperty) { theValue in
print("-----> The Value is \(theValue)") // <--- this will be executed
}
}
ObservableObject and #Published are part of the Combine framework if you aren't using Combine then you shouldn't be using a class for your view data. Instead, you should be using SwiftUI as designed and avoid heavy objects and either put the data in the efficient View data struct or make a custom struct as follows:
import SwiftUI
struct MyConfig {
var myProperty: Bool = false
mutating func myMethod() {
myProperty = !myProperty
}
}
struct ContentView: View {
#State var config = MyConfig()
var body: some View {
Text("Hello, World!")
.onTapGesture {
config.myMethod()
}
}
}
Old answer:
Try onChange instead
https://developer.apple.com/documentation/swiftui/scrollview/onchange(of:perform:)
.onChange(of: viewModel.myProperty) { newValue in
print("newValue \(newValue)")
}
But please don't use the View Model object pattern in SwiftUI, try to force yourself to use value types like structs for all your data as SwiftUI was designed. Property wrappers like #State will give you the reference semantics you are used to with objects.
What i have stumped across is that when i pass a Binding<> as a parameter in a ViewModel as you will see below, it doesn't always work as intended. It works in iOS 15 but not in iOS 16. This reduces the capability to create subviews to handle this without sending the entire Holder object as a #Binding down to it's subview, which i would say would be bad practice.
So i have tried to minimize this as much as possible and here is my leasy amount of code to reproduce it:
import SwiftUI
enum Loadable<T> {
case loaded(T)
case notRequested
}
struct SuperBinder {
let loadable: Binding<Loadable<ContentView.ViewModel>>
let toggler: Binding<Bool>
}
struct Holder {
var loadable: Loadable<ContentView.ViewModel> = .notRequested
var toggler: Bool = false
func generateContent(superBinder: SuperBinder) {
superBinder.loadable.wrappedValue = .loaded(.init(toggleBinder: superBinder.toggler))
}
}
struct ContentView: View {
#State var holder = Holder()
var superBinder: SuperBinder {
.init(loadable: $holder.loadable, toggler: $holder.toggler)
}
var body: some View {
switch holder.loadable {
case .notRequested:
Text("")
.onAppear(perform: {
holder.generateContent(superBinder: superBinder)
})
case .loaded(let viewModel):
Toggle("testA", isOn: viewModel.toggleBinder) // Works but doesn't update UI
Toggle("testB", isOn: $holder.toggler) // Works completly
// Pressing TestA will even toggle TestB
// TestB can be turned of directly but has to be pressed twice to turn on. Or something?
}
}
struct ViewModel {
let toggleBinder: Binding<Bool>
}
}
anyone else stumbled across the same problem? Or do i not understand how binders work?
I have a custom ViewModifier which simply returns the same content attached with a onReceive modifier, the onReceive is not triggered, here is a sample code that you can copy, paste and run in XCode:
import SwiftUI
import Combine
class MyViewModel: ObservableObject {
#Published var myProperty: Bool = false
}
struct ContentView: View {
#ObservedObject var viewModel: MyViewModel
var body: some View {
Text("Hello, World!")
.modifier(MyOnReceive(viewModel: viewModel))
.onTapGesture {
self.viewModel.myProperty = true
}
}
}
struct MyOnReceive: ViewModifier {
#ObservedObject var viewModel: MyViewModel
func body(content: Content) -> some View {
content
.onReceive(viewModel.$myProperty) { theValue in
print("The Value is \(theValue)") // <--- this is not executed
}
}
}
is SwiftUI designed to disallow onReceive to execute inside a ViewModifier or is it a bug ? I have a view in my real life project that gets bigger with some business logic put inside onReceive, so I need to clean that view by separating it from onReceive.
ok, this works for me:
func body(content: Content) -> some View {
content
.onAppear() // <--- this makes it work
.onReceive(viewModel.$myProperty) { theValue in
print("-----> The Value is \(theValue)") // <--- this will be executed
}
}
ObservableObject and #Published are part of the Combine framework if you aren't using Combine then you shouldn't be using a class for your view data. Instead, you should be using SwiftUI as designed and avoid heavy objects and either put the data in the efficient View data struct or make a custom struct as follows:
import SwiftUI
struct MyConfig {
var myProperty: Bool = false
mutating func myMethod() {
myProperty = !myProperty
}
}
struct ContentView: View {
#State var config = MyConfig()
var body: some View {
Text("Hello, World!")
.onTapGesture {
config.myMethod()
}
}
}
Old answer:
Try onChange instead
https://developer.apple.com/documentation/swiftui/scrollview/onchange(of:perform:)
.onChange(of: viewModel.myProperty) { newValue in
print("newValue \(newValue)")
}
But please don't use the View Model object pattern in SwiftUI, try to force yourself to use value types like structs for all your data as SwiftUI was designed. Property wrappers like #State will give you the reference semantics you are used to with objects.
I am using SwiftUI and I am trying to achieve a simple logical action but unable to understand SwiftUI action hierarchy.
I have one API call something like this,
final class TaskData: ObservableObject {
#Published var updatedFields = false
#Published var updateMsg = ""
func updateFields()
{
//Some API Call
.whenSuccess { (response) in
DispatchQueue.main.async {
self.updatedFields = true
self.updateMsg = "Successfully updated fields"
//Send Request to dismiss current View ???
}
}
}
}
Now, I have a View something like this, and on a request I want to dismiss this View, but I am unable to find any method for that,
struct TaskView: View {
#Environment(\.presentationMode) var currentView: Binding<PresentationMode>
#EnvironmentObject var taskData: TaskData
var body : some View {
//Some Views here ////
//Need Some code here to dismiss currentView?????
.navigationBarItems(trailing: Button(action: {
}, label: {
Text("Done")
}).onTapGesture {
self.taskData.updateFields() // Method Call to Update fields
})
}
if someone can explain this thing in a little detail as I am newbie to SwiftUI, I have seen a lot tutorial but unable to understand this structure of swift.
It is not shown how TaskView is presented, but having presentationMode in give code snapshot let's assume that it is valid, so the approach might be as follows
#Environment(\.presentationMode) var presentationMode //better to name it same,
//type is extracted from Environment
#EnvironmentObject var taskData: TaskData
var body : some View {
//Some Views here ////
SomeView()
.onReceive(taskData.$updatedFields) { success in
if success {
self.presentationMode.wrappedValue.dismiss() // dismiss self
}
}
...
I am producing the situation on WatchOS with the following code
struct Modal : View {
#Binding var showingModal : Bool
init(showingModal : Binding<Bool>){
self._showingModal = showingModal
print("init modal")
}
var body: some View {
Button(action: {
self.showingModal.toggle()
}, label: {
Text("TTTT")
})
}
}
struct ContentView: View {
#State var showingModal = false
var body: some View {
Button(action: {
self.showingModal.toggle()
}, label: {
Text("AAAA")
}).sheet(isPresented: $showingModal, content: {Modal(showingModal: self.$showingModal)})
}
}
Every time I press the button in the master view to summon the modal with .sheet, Two instances of the modal view are created.
Could someone explain this phenomenon?
I tracked this down in my code to having the following line in my View:
#Environment(\.presentationMode) var presentation
I had been doing it due to https://stackoverflow.com/a/61311279/155186, but for some reason that problem seems to have disappeared for me so I guess I no longer need it.
I've filed Feedback FB7723767 with Apple about this.
It is probably a bug, as of Xcode 11.4.1 (11E503a).
Beware, that if for example initializing view models (or anything else for that matter) like so:
.sheet(isPresented: $isEditingModalPresented) {
LEditView(vm: LEditViewModel(), isPresented: self.$isEditingModalPresented)
}
the VM will be initialized twice.
Comment out/remove the init() method from Modal with everything else the same. You should be able to solve the issue of two instances of Modal being created, its because you are explicitly initializing the binding (showingModal) in the init() of Modal. Hope this makes sense.
private let uniqueId: String = "uniqueId"
Button(action: {
self.showingModal.toggle()
}, label: {
Text("AAAA")
})
.sheet(isPresented: $showingModal) {
Modal(showingModal: self.$showingModal)
.id("some-unique-id")
}
Ex:
.id(self.uniqueId)
Add unique id to your .sheet and not't worry :)
But, do not use UUID(), because sheet view will be represented on every touch event