I have a very simple app which contains two views that are tied together with a NavigationLink. In the first view, ContentView, I can see updates to my ObservedObject as expected. However, when I go to the next View, it seems that the code based on the ObservedObject does not recognize changes.
ContentView.swift (The working view):
import SwiftUI
struct ContentView: View {
#ObservedObject var toggleObject = ToggleObject()
var body: some View {
NavigationView {
VStack(spacing: 15) {
Toggle(isOn: self.$toggleObject.isToggled) {
Text("Toggle:")
}
if self.toggleObject.isToggled == true {
Text("ON")
}
else {
Text("OFF")
}
NavigationLink(destination: ShowToggleView()) {
Text("Show Toggle Status")
}
}
}
}
}
ShowToggleView.swift (The view that does not behave as I expect it to):
import SwiftUI
struct ShowToggleView: View {
#ObservedObject var toggleObject = ToggleObject()
var body: some View {
Form {
Section {
if self.toggleObject.isToggled {
Text("Toggled on")
}
else {
Text("Toggled off")
}
}
}
}
}
All of this data is stored in a simple file, ToggleObject.swift:
import SwiftUI
class ToggleObject: ObservableObject {
#Published var isToggled = false
}
When I toggle it on in the first View I see the text "ON" which is expected, but when I go into the next view it shows "Toggled off" no matter what I do in the first View... Why is that?
Using Xcode 11.5 and Swift 5
You are almost doing everything correct. However, you are creating another instance of ToggleObject() in your second view, which overrides the data. You basically only create one ObservedObject and then pass it to your subview, so they both access the same data.
Change it to this:
struct ShowToggleView: View {
#ObservedObject var toggleObject : ToggleObject
And then pass the object to that view in your navigation link...
NavigationLink(destination: ShowToggleView(toggleObject: self.toggleObject)) {
Text("Show Toggle Status")
}
Related
I am developing an application using SwiftUI (XCode 12.5.1) and every time one of my View appears after exactly two links of "NavigationLink" everything that is inside a Form is shifted slightly to the left, once the appearing animation is over. The following video shows whats going on : the first two times I open the view, everything is fine. The next two times, when the view is accessed from nested NavigationLink, a slight shift to the left is done once the appearing animation is over.
https://www.dropbox.com/s/k3gjc42xlqp2auf/leftShift.mov?dl=0
I have the same problem on both the simulator and a real device (an iPhone). Here is the project: https://www.dropbox.com/s/l8r5hktg6lz69ob/Bug.zip?dl=0 . The main code is available below.
Here is the main view ContentView.swift
import SwiftUI
struct ContentView: View {
var body: some View {
NavigationView {
List {
NavigationLink(destination: PersonView()) {
Text("Person")
}
NavigationLink(destination: IndirectView()) {
Text("Indirect")
}
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
Here is the indirect view, IndirectView.swift
import SwiftUI
struct IndirectView: View {
var body: some View {
List {
NavigationLink(destination: PersonView()) {
Text("Person")
}
}
}
}
and the person view, PersonView.swift
import SwiftUI
struct PersonView: View {
var body: some View {
Form {
VStack(alignment: .leading, spacing: 5) {
Text("Last Name")
.font(.system(.subheadline))
.foregroundColor(.secondary)
Text("Fayard")
}
}
}
}
Do you have any idea on what's causing this shift?
Thanks for your help
Francois
Frankly saying I have not idea what causes the problem, but here is the fix: add this line of code no your NavigaitonView
NavigationView {
// everything else
}.navigationViewStyle(StackNavigationViewStyle())
I have a TabView with two tabs in a SwiftUI lifecycle app, one of them has complex view structure: NavigationView with a lot of sub-views inside, i.e.: NavigationLinks and their DestinationViews are spread on multiple levels down the view tree, each sub-view on its own is another view hierarchy with sheets and / or other DestinationViews. At some point inside this hierarchy, I want to reset the TabView to its original state which is displaying the first most view, so the user can restart their journey right at that state, as they were to open the app for the first time, so it's kinda impossible to track down something like isActive & isPresented bindings to pop-off or dismiss the views and sheets.
I thought of wrapping the TabView inside another view: RootView in an attempt to find an easy way to recreate that TabView from scratch or something like refreshing / resetting the TabView, but couldn't find a clew on how to do it.
Here's my code snippet:
#main
struct TestApp: App {
var body: some Scene {
WindowGroup {
RootView()
}
}
}
struct RootView: View {
var body: some View {
ContentView()
}
}
struct ContentView: View {
var body: some View {
TabView { // <-- I need to reset it to its original state
View1() // <---- this view has complex view hierarchy
.tabItem {
Text("Home")
}.tag(0)
View2()
.tabItem {
Text("Settings")
}.tag(1)
}
}
}
p.s. I'm not looking for "popping off the view to root view", because this can't be done when there are many active NavigationLink destinations where the user might open one of the sheets and start a new navigation journey inside the sheet.
****** UPDATE ******
I've created a new Environment value to hold a boolean that should indicate whether the TabView should reset or not, and I've tracked every isPresented and isActive state variables in every view and reset them once that environment value is set to true like this:
struct ResetTabView: EnvironmentKey {
static var defaultValue: Binding<ResetTabObservable> = .constant(ResetTabObservable())
}
extension EnvironmentValues {
var resetTabView: Binding<ResetTabObservable> {
get { self[ResetTabView.self] }
set { self[ResetTabView.self] = newValue }
}
}
class ResetTabObservable: ObservableObject {
#Published var newValue = false
}
in every view that will present a sheet or push a new view I added something like this:
struct View3: View {
#State var showSheet = false
#Environment(\.resetTabView) var reset
var body: some View {
Text("This is view 3")
Button(action: {
showSheet = true
}, label: {
Text("show view 4")
})
.sheet(isPresented: $showSheet) {
View4()
}
.onReceive(reset.$newValue.wrappedValue, perform: { val in
if val == true {
showSheet = false
}
})
}
}
and in the last view (which will reset the TabView) I toggle the Environment value like this:
struct View5: View {
#Environment(\.resetTabView) var reset
var body: some View {
VStack {
Text("This is view 5")
Button(action: {
reset.newValue.wrappedValue = true
}, label: {
Text("reset tab view")
})
}
}
}
This resulted in awkward dismissal for views:
What i do for this is i make all my presentation bindings be stored using #SceneStorage("key") (instead of #State) this way they not only respect state restoration ! but you can also access them throughout your app easily by using the same key. This post gives a good example of how this enables the switching from Tab to Sidebar view on iPad.
I used this in my apps so if i have a button or something that needs to unwind many presentations it can read on all of these values and reset them back to wanted value without needing to pass around a load of bindings.
If I create a new #State variable, when does it get destroyed? Does it live for the lifetime of the parent UIHostingController?
As far as I can find, it is not documented. This is relevant because I don't understand how to clean up after myself if I create an ObservableObject as State somewhere in the view hierarchy.
import SwiftUI
struct Example: View {
#State private var foo = Foo()
var body: some View {
Text("My Great View")
}
}
class Foo: ObservableObject {
deinit {
// When will this happen?
print("Goodbye!")
}
}
Assuming:
struct Example: View {
#State private var foo = Foo()
var body: some View {
Text("My Great View")
}
}
class Foo: ObservableObject {
init() {
print(#function)
}
deinit {
print(#function)
}
}
The issue is that a View type is a struct, and it's body is not a collection of functions that are executed in real-time but actually initialized at the same time when View's body is rendered.
Problem Scenario:
struct ContentView: View {
#State var isPresented = false
var body: some View {
NavigationView {
NavigationLink(destination: Example()) {
Text("Test")
}
}
}
}
If you notice, Example.init is called before the navigation even occurs, and on pop Example.deinit isn't called at all. The reason for this is that when ContentView is initialized, it has to initialize everything in it's body as well. So Example.init will be called.
When we navigate to Example, it was already initialized so Example.init is not called again. When we pop out of Example, we just go back to ContentView but since Example might be needed again, and since it is not created in real-time, it is not destroyed.
Example.deinit will be called only when ContentView has to be removed entirely.
I wasn't sure on this but found another article talking about a similar issue here:
SwiftUI and How NOT to Initialize Bindable Objects
To prove this, lets ensure the ContentView is being completely removed.
The following example makes use of an action sheet to present and remove it from the view hierarchy.
Working Scenario:
struct ContentView: View {
#State var isPresented = false
var body: some View {
Button(action: { self.isPresented.toggle() }) {
Text("Test")
}
.sheet(isPresented: $isPresented) {
Example()
.onTapGesture {
self.isPresented.toggle()
}
}
}
}
PS: This applies to classes even if not declared as #State, and does not really have anything to do with ObservableObject.
In iOS 14, the proper way to do this is to use #StateObject. There is no safe way to store a reference type in #State.
I am working on a project that at some point it receives a notification. When that happens, I need to show a View. I am not able to catch notification from any View so I am looking for a way to change to control it from outside of View structs. After the View's purpose is done, I need to dismiss it where the app left off. Think like the native behaviour when there is an active call.
I thought I could use sheet however I could not find any way to trigger it for every View that could be active when the notifications come. Or maybe trying to extend native View class would work but again, no luck finding a tutorial.
Any help will be appreciated.
Just update your model based on notification. There is not necessary to define .sheet (modal view) everywhere in your view hierarchy. Doing it in root view should be enough.
To demonstrate that (copy - paste - run) I create small project where I mimic notification with SwiftUI Toggle.
import SwiftUI
class Model: ObservableObject {
#Published var show = false
}
struct SubView: View {
#EnvironmentObject var model: Model
var tag: Int
var body: some View {
VStack {
NavigationLink(destination: SubView(tag: tag + 1).environmentObject(model)) {
Text("subview \(tag)")
}
if tag == 2 {
Toggle(isOn: $model.show) {
Text("toggle")
}.padding()
}
}.navigationBarTitle("subview \(tag)")
}
}
struct ContentView: View {
#ObservedObject var model = Model()
var body: some View {
NavigationView {
SubView(tag: 0).environmentObject(model)
}.sheet(isPresented: $model.show) {
Text("sheet")
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
with the result
As detailed here (on an iOS topic), the following code can be used to make a SwiftUI View dismiss itself:
#Environment(\.presentationMode) var presentationMode
// ...
presentationMode.wrappedValue.dismiss()
However, this approach doesn't work for a native (not Catalyst) macOS NavigationView setup (such as the below), where the selected view is displayed alongside the List.
Ideally, when any of these sub-views use the above, the list would go back to having nothing selected (like when it first launched); however, the dismiss function appears to do nothing: the view remains exactly the same.
Is this a bug, or expected macOS behaviour?
Is there another approach that can be used instead?
struct HelpView: View {
var body: some View {
NavigationView {
List {
NavigationLink(destination:
AboutAppView()
) {
Text("About this App")
}
NavigationLink(destination:
Text("Here’s a User Guide")
) {
Text("User Guide")
}
}
}
}
}
struct AboutAppView: View {
#Environment(\.presentationMode) var presentationMode
public var body: some View {
Button(action: {
self.dismissSelf()
}) {
Text("Dismiss Me!")
}
}
private func dismissSelf() {
presentationMode.wrappedValue.dismiss()
}
}
FYI: The real intent is for less direct scenarios (such as triggering from an Alert upon completion of a task); the button setup here is just for simplicity.
The solution here is simple. Do not use Navigation View where you need to dismiss the view.
Check the example given by Apple https://developer.apple.com/tutorials/swiftui/creating-a-macos-app
If you need dismissable view, there is 2 way.
Create a new modal window (This is more complicated)
Use sheet.
Following is implimenation fo sheet in macOS with SwiftUI
struct HelpView: View {
#State private var showModal = false
var body: some View {
NavigationView {
List {
NavigationLink(destination:
VStack {
Button("About"){ self.showModal.toggle() }
Text("Here’s a User Guide")
}
) {
Text("User Guide")
}
}
}
.sheet(isPresented: $showModal) {
AboutAppView(showModal: self.$showModal)
}
}
}
struct AboutAppView: View {
#Binding var showModal: Bool
public var body: some View {
Button(action: {
self.showModal.toggle()
}) {
Text("Dismiss Me!")
}
}
}
There is also a 3rd option to use ZStack to create a Modal Card in RootView and change opacity to show and hide with dynamic data.