ok I'm working on a first swiftui app as a way of learning and have used conditionals to colour some buttons. The problem is when the related state changes (Bool) the conditional isn't being updated. I thought this was to do with a UI redraw not being triggered due to state however I can't seem to figure out a solution to that.
Background info: task is an instance of the Task class (passed in from another view) which is an array on the ModelData Environment object. when the button is clicked the related value (isHotList) is indeed changed but the image colour isn't changed.
#EnvironmentObject var modelData: ModelData
var task: Task
Button(action: {
task.isHotList.toggle()
}){
Image(systemName: "flame.fill")
.foregroundColor(task.isHotList ? Color.orange : Color.gray)
}
Make the Test an observable object, like
class Task: ObservableObject {
#Published var isHotList = false
// ... other content here
}
and make test property in view wrapped into ObservedObject, like
#EnvironmentObject var modelData: ModelData
#ObservedObject var task: Task // << here !!
Alternatively make the Task as struct and then you can use either #State or #Binding for task property (depending on your design).
Related
I have a VM that is implemented as follows:
LoginViewModel
class LoginViewModel: ObservableObject {
var username: String = ""
var password: String = ""
}
In my ContentView, I use the VM as shown below:
#StateObject private var loginVM = LoginViewModel()
var body: some View {
NavigationView {
Form {
TextField("User name", text: $loginVM.username)
TextField("Password", text: $loginVM.password)
Every time I type something in the TextField it shows the following message in the output window:
Binding<String> action tried to update multiple times per frame.
Binding<String> action tried to update multiple times per frame.
Binding<String> action tried to update multiple times per frame.
It is a message and not an error.
If I decorate my username and password properties with #Published then the message goes away but the body is rendered each time I type in the TextField.
Any ideas what is going on and whether I should use #Published or not. I don't think I will gain anything from putting the #Published attribute since this is a one-way binding and I don't want to display anything on the view once the username changes.
If I decorate my username and password properties with #Published then the message goes away
This is the correct solution. You need to use #Published on those properties because that is how SwiftUI gets notified when the properties change.
the body is rendered each time I type in the TextField
That is fine. Your body method is not expensive to compute.
I don't think I will gain anything from putting the #Published attribute since this is a one-way binding
You cannot be sure SwiftUI will work correctly (now or in future releases) if you don't use #Published. SwiftUI expects to be notified when the value of a Binding changes, even when a built-in SwiftUI component like TextField causes the change.
For the simple case - the state is kept in the same view or in a ModelSupport class, consists of strings or other primitive types, and there's only one of each, #Published will work fine.
I got this error with a model class containing an array of structs and using a List, and every time you type inside a TextField inside a list (or every time you select an item in a list), the view gets refreshed, and the error gets triggered.
I am thus using a DelayedTextField:
struct DelayedTextField: View {
var title: String = ""
#Binding var text: String
#State private var tempText: String = ""
var body: some View {
TextField(title, text: $tempText, onEditingChanged: { editing in
if !editing {
$text.wrappedValue = tempText
}
})
.onAppear {
tempText = text
}
}
}
and the binding update error is no more.
I have an app where there are multiple screens with textfields to create some new object. When the user selects "Create" on the last screen, an API call is performed which creates the new object.
From there I want to push the detail page of the newly created object, and (when the view is no longer visible) remove all the screens with textfields (as that is no longer relevant, and would only cause confusion. Luckily there is only one screen that should remain before the detailpage.
In UIKit, this would be performed by doing a push on the navigationController, and then editing the viewControllers array of the navigationController in the viewDidLoad of the new screen.
If I am correct, there is no way to edit the views in a SwiftUI NavigationView, so how can I perform this action in SwiftUI?
I solved it by adding an id to the NavigationView, and then setting this to another id in the viewmodel when it should reset.
Like this:
struct MyView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
NavigationView {
// ...
}
.id(viewModel.id)
}
}
In the viewmodel:
class ViewModel: ObservableObject {
#Published var id = UUID().uuidString
func reset() {
id = UUID().uuidString
}
}
This resets the NavigationView as Swift thinks it's a different view because the id changed.
I created an ObservableObject that gathers data and a view that depends on this object. More specifically some parts of the UI depend on one property of it and other parts depend on other properties.
The way ObservableObject works is that if any of its Published property gets updated (event if it does not change) it sends an objectWillChange notification that triggers updates for subscribed views.
However, I did expect that only the parts of the views that depends on an ObservableObject property that actually changed would be updated, not the entire view because body computations are expensive.
Unfortunately this it not the behavior I observed during my experiments. For instance in the following code the List view depends only on the color dynamic property of the ObservedObject "preferences" and the TextField updates only the text property of the observed object. I observed with the debugPrint's that when I type text the List and its rows gets updated each time even if it does not depend on text.
struct ContentView: View {
#State private var list = ["foo", "bar", "baz"]
#StateObject private var preferences = Preferences()
var body: some View {
VStack {
List(list, id: \.self) { element in
Text(element)
.foregroundColor(preferences.color)
.debugPrint("Row view updated")
}
Spacer()
HStack {
TextField("Text", text: $preferences.text)
.debugPrint("Text field view updated")
Button("Toogle Color", action: toggleColor)
.debugPrint("Button view updated")
}
}
.padding()
.debugPrint("Content view updated")
}
func toggleColor() {
preferences.color = [.blue, .green, .orange, .red].randomElement()!
}
}
final class Preferences: ObservableObject {
#Published var color: Color = .blue
#Published var text: String = ""
}
extension View {
func debugPrint(_ elements: Any...) -> Self {
#if DEBUG
print(elements)
return self
#else
return self
#endif
}
}
Is this the correct and intended behavior? How the optimal behavior I described above could be obtained, i.e. not calling body when the ObservedObject changes but only the components that depends on specific properties?
I observed in bigger SwiftUI projects that this behavior can greatly slow down the application and is not easily debuggable because unique state is often enforced through heavy ObservedObjects (or StateObject) injected at the root view and used in many places. I Observed this behavior even with small lists of components with heavy UI layout.
Note 1: I was bugged by the StateObject definition which suggests that only the views that depend on those properties are updated (and not when the StateObject changes).
SwiftUI creates a new instance of the object only once for each
instance of the structure that declares the object. When published
properties of the observable object change, SwiftUI updates the parts
of any view that depend on those properties [...]
Note 2: The issue totally disappear if I define the List in its own component, the rendering is fast:
struct ListView: View {
let list: [String] // Also works with a #Binding
let color: Color // Also works if it would be `preferences`
var body: some View {
List {
ForEach(list, id: \.self) { element in
Row(text: element, color: color)
}
}
}
}
Why in this case the view updates are fast?
I am trying out this quick start for SwiftUI and Combine in order to try and understand how to connect my Realm database to Combine.
The example observes a RealmSwift.List and keeps a table populated with its data. This is is a linked list to a child class. I'm wondering how to observe a Results collection so I can keep track of any changes to an entire Realm class.
For example, let's say I have a Workspace class:
class Workspace: Object, ObjectKeyIdentifiable{
#objc dynamic var id = UUID().uuidString
#objc dynamic var name = ""
#objc dynamic var archived = false
}
In the state object, I can set up a Results<Workspace> variable like this:
class AppState: ObservableObject {
#Published var workspaces: Results<Workspace>?
var cancellables = Set<AnyCancellable>()
init(){
let realmPublisher = PassthroughSubject<Realm, Error>()
realmPublisher
.sink(receiveCompletion: { _ in }, receiveValue: { realm in
//Get the Results
self.workspaces = realm.objects(Workspace.self)
})
.store(in: &cancellables)
realmPublisher.send(try! Realm())
return
}
}
But when it comes time to observe the object, I can't because Results isn't an object (I assume).
struct ContentView: App {
#ObservedObject var state = AppState()
var view: some View {
ItemsView(workspaces: state.workspaces!)
}
var body: some Scene {
WindowGroup {
view.environmentObject(state)
}
}
}
struct ItemsView: View {
#ObservedObject var workspaces: Results<Workspace> //<!-- Error
var body: some View {
//...
}
}
Xcode gives a syntax error on the workspaces property:
Property type 'Results' does not match that of the 'wrappedValue' property of its wrapper type 'ObservedObject'
Is it possible to observe a set of Results just like we can have a notification listener on a collection of Results?
Technically, you could hook up a sink to state.workspaces (state.$workspaces.sink()), but in this case, I think you're overcomplicating the problem.
You already have an #ObservableObject in your ContentView (AppState) that is managing the results for you. So, change ItemsView to just take this as a parameter:
var workspaces: Results<Workspace>?
It doesn't need to be an #ObservedObject -- either way, whether it's getting observed in that view or it's parent view, it's going to get re-rendered. It does have to be optional here, since it's an optional value on your AppState, unless you want to keep passing it with the force unwrap (!), but that's generally a bad idea, since it'll crash if it ever is in fact nil.
Also, above, in your Realm code, make sure it's matching the tutorial that you were following. For example, you have Publisher.sink which should really be realmPublisher.sink
You are correct, Results is a struct, and therefore cannot be covered by #StateObject or #ObservedObject. Your workaround is suitable for now.
Once https://github.com/realm/realm-cocoa/pull/7045 is released, you will be able to use one of the new Realm property wrappers to embed your Results into the view directly. At the time of this posting, that would be #FetchRealmResults, but that is subject to change.
In a SwiftUI app, I have an ObservableObject that keeps track of user settings:
class UserSettings: ObservableObject {
#Published var setting: String?
}
I have a view model to control the state for my view:
class TestViewModel: ObservableObject {
#Published var state: String = ""
}
And I have my view. When the user setting changes, I want to get the view model to update the state of the view:
struct HomeView: View {
#EnvironmentObject var userSettings: UserSettings
#ObservedObject var viewModel = TestViewModel()
var body: some View {
Text(viewModel.state)
.onReceive(userSettings.$setting) { setting in
self.viewModel.state = setting
}
}
}
When the UserSettings.setting is changed in another view it causes onReceive on my view to get called in an infinite loop, and I don't understand why. I saw this question, and that loop makes sense to me because the state of the ObservableObject being observed is being changed on observation.
However, in my case I'm not changing the observed object (environment object) state. I'm observing the environment object and changing the view model state which redraws the view.
Is the view redrawing what's causing the issue here? Does onReceive get called everytime the view is redrawn?
Is there a better way of accomplishing what I'm trying to do?
EDIT: this is a greatly simplified version of my problem. In my app, the view model takes care of executing a network request based on the user's settings and updating the view's state such as displaying an error message or loading indicator.
Whenever you have an onReceive with an #ObservedObject that sets another (or the same) published value of the #ObservedObject you risk creating an infinite loop if those published attributes are being displayed somehow.
Make your onReceive verify that the received value is actually updating a value, and not merely setting the same value, otherwise it will be setting/redrawing infinitely. In this case, e.g.,:
.onReceive(userSettings.$setting) { setting in
if setting != self.viewModel.state {
self.viewModel.state = setting
}
}
From described scenario I don't see the reason to duplicate setting in view model. You can show the value directly from userSettings, as in
struct HomeView: View {
#EnvironmentObject var userSettings: UserSettings
#ObservedObject var viewModel = TestViewModel()
var body: some View {
Text(userSettings.setting)
}
}
You might be able to prevent infinite re-rendering of the view body by switching your #ObservedObject to #StateObject.