I'm trying to create a IOS app with SwiftUI that uses NavigationViewand hides the Navigation Bar on the first view (and only on the first one).
So I created an ObservableObject
class NavBarShowViewModel: ObservableObject {
#Published var isHidden: Bool = true
}
and in my Content View
struct ContentView: View {
#ObservedObject var navBarShowViewModel = NavBarShowViewModel()
var body: some View {
NavigationView {
Home()
.navigationBarHidden(self.navBarShowViewModel.isHidden)
}
.environmentObject(self.navBarShowViewModel)
}
}
Now in Home I have:
struct Home: View {
#EnvironmentObject var navBarShowViewModel: NavBarShowViewModel
var body: some View {
VStack {
HStack {
NavigationLink(destination: FirstPage()) {
Text("Go!")
}
Text("Hello World")
Spacer()
}
.navigationBarTitle("Home")
}
.onAppear(perform: {
self.navBarShowViewModel.isHidden = true
})
}
}
Now FirstPage() has the exact structure of Home(), except that has a different title
.navigationBarTitle("First Page")
and onAppear has the following code:
.onAppear(perform: {
self.navBarShowViewModel.isHidden = false
})
With this setup, the app works.
But if inside FirstPage() I navigate further, for example going to SecondPage() (which is for sake of simplicity, identical to FirstPage() with a different title) and then hitting back until I return to Home, onAppear here on Home() is not called, so it shows the navigation bar title.
Could someone explain this?
It is about how SwiftUI engine tracks views and if it really appears... anyway, what it is can be determined as it is how child views appear/disappear on navigation stack, so possible solution is to add onDisappear in FirstPage, like
struct FirstPage: View {
#EnvironmentObject var navBarShowViewModel: NavBarShowViewModel
var body: some View {
... other code here
.onAppear(perform: {
self.navBarShowViewModel.isHidden = false
})
.onDisappear(perform: {
self.navBarShowViewModel.isHidden = true
})
}
}
Tested with Xcode 12.4 / iOS 14.4
Related
I have the following:
#State private var showNext = false
...
NavigationStack {
VStack {
NavigationLink(destination: NextView(showSelf: $showNext),
isActive: $showNext) { EmptyView() }
Button("Show Next") {
showNext = true
}
}
}
...
struct NextView: View {
#Binding var showSelf: Bool
var body: some View {
Text("Next")
.navigationTitle("Next")
Button("Dismiss") {
showSelf = false
}
.padding(30)
}
}
When tapping Show Next, the NextView is shown as expected.
But when tapping Dismiss, nothing happens.
Turns out that showSelf was already false before it's set to false. So it seems something went wrong with passing the binding into NextView.
What could be wrong?
The issue was caused by NavigationStack. When I replaced it with NavigationView it worked as expected.
The isActive binding of NavigationLink does not appear to work (or to be supported) when embedded in a NavigationStack.
isActive binding is for NavigationView, try:
NavigationView {
...
}
.navigationViewStyle(.stack)`
You are trying to mix code for iOS >= 16 (NavigationStack) and for iOS < 16 (the previous way to handle NavigationLink). Similarly for the dismiss part, which is iOS < 15.
Here is your code for iOS 16:
import SwiftUI
struct ContentView: View {
var body: some View {
NavigationStack {
VStack {
NavigationLink {
NextView()
} label: {
Text("Show next view")
}
}
}
}
}
struct NextView: View {
#Environment(\.dismiss) private var dismiss
var body: some View {
VStack {
Text("You are in the next view")
Button("Dismiss", action: dismiss.callAsFunction)
}
.navigationTitle("Next")
}
}
I have used the simplest construction of NavigationLink. A more complex one would be used in conjunction with .navigationDestination. The best examples I have found are here:
https://swiftwithmajid.com/2022/06/15/mastering-navigationstack-in-swiftui-navigator-pattern/
https://swiftwithmajid.com/2022/06/21/mastering-navigationstack-in-swiftui-deep-linking/
https://www.pointfree.co/blog/posts/78-reverse-engineering-swiftui-s-navigationpath-codability
And if you want to dive more into very strange behaviour of the stack, you can look at my post here: Found a strange behaviour of #State when combined to the new Navigation Stack - Is it a bug or am I doing it wrong?
If you need to produce code for iOS < 16, you should replace NavigationStack with NavigationView and work from there.
I have an app with a few tabs, and on one of those there is a NavigationLink which nests a couple of times.
I want to be able to switch tabs, and when going back to the other tab to have unwound all links to the root view.
I have seen these: https://stackoverflow.com/a/67014642/1086990 and https://azamsharp.medium.com/unwinding-segues-in-swiftui-abdf241be269 but they seem to be focusing on unwinding when active on the view, not switching from it.
struct MyTabView: View {
var body: some View {
TabView {
TabOne().tabItem { Image(systemName: "1.square") }
TabTwo().tabItem { Image(systemName: "2.square") }
}
}
}
struct TabOne: View {
var body: some View {
Text("1")
}
}
struct TabTwo: View {
var body: some View {
NavigationView {
NavigationLink("Go to sub view") {
TabTwoSub()
}
}
}
}
struct TabTwoSub: View {
var body: some View {
Text("Tapping \(Image(systemName: "1.square")) doesnt unwind this view back to the root of the NavigationView")
.multilineTextAlignment(.center)
}
}
Maybe I've missed something fairly basic but nothing seems to come up from searches on unwinding views when switching tabs.
I tried using the NavigationLink(isActive: , destination: , label: ) from the other SO answer but couldn't get it working in the root MyTabView.
I thought about using UserDefaults to set a isActive bool state and if not try and unwind the navigation, but that didn't seem very swifty to do.
What is happening
You'll need to keep track of the tab selection in the parent view and then pass that into the child views so that they can watch for changes. Upon seeing a change in the selection, the child view can then reset a #State variable that change the isActive property of the NavigationLink.
class NavigationManager : ObservableObject {
#Published var activeTab = 0
}
struct MyTabView: View {
#StateObject private var navigationManager = NavigationManager()
var body: some View {
TabView(selection: $navigationManager.activeTab) {
TabOne().tabItem { Image(systemName: "1.square") }.tag(0)
TabTwo().tabItem { Image(systemName: "2.square") }.tag(1)
}.environmentObject(navigationManager)
}
}
struct TabOne: View {
var body: some View {
Text("1")
}
}
struct TabTwo: View {
#EnvironmentObject private var navigationManager : NavigationManager
#State private var linkActive = false
var body: some View {
NavigationView {
NavigationLink("Go to sub view", isActive: $linkActive) {
TabTwoSub()
}
}.onChange(of: navigationManager.activeTab) { newValue in
linkActive = false
}
}
}
struct TabTwoSub: View {
var body: some View {
Text("Tapping \(Image(systemName: "1.square")) doesnt unwind this view back to the root of the NavigationView")
.multilineTextAlignment(.center)
}
}
Note: this will result in a "Unbalanced calls to begin/end appearance transitions" message in the console -- in my experience, this is not an error and not something we have to worry about
Whenever my code gets too big, SwiftUI starts acting weird and generates an error:
"The compiler is unable to type-check this expression in reasonable time; try breaking up the expression into distinct sub-expressions"
So I started breaking up my code into Extracted Subviews, one of the problems I came across is how to dismiss a view from a subtracted subview.
Example: we have here LoginContentView this view contains a button when the button is clicked it will show the next view UsersOnlineView.
struct LoginContentView: View {
#State var showUsersOnlineView = false
var body: some View {
Button(action: {
self.showUsersOnlineView = true
}) {
Text("Show the next view")
}
.fullScreenCover(isPresented: $showUsersOnlineView, content: {
UsersOnlineView()
})
}
On the other hand, we have a button that is extracted to subview, to dismiss the modal and go back to the original view:
import SwiftUI
struct UsersOnlineView: View {
var body: some View {
ZStack {
VStack {
CloseViewButton()
}
}
}
}
struct CloseViewButton: View {
var body: some View {
Button(action: {
// Close the Modal
}) {
Text("Close the view")
}
}
}
Give the sbview the state property that defines if the view is shown.
struct CloseViewButton: View {
#Binding var showView: Bool
var body: some View {
Button(
ShowView = false
}) {
Text("Close the view")
}
}
}
When you use the sub view give it the property
CloseButtonView(showView: $showOnlineView)
To allow the sub view to change the isShown property it needs to get a binding.
On the presentation mode. I think this only works with Swiftui presentations like sheet and alert.
The simplest solution for this scenario is to use presentationMode environment variable:
struct CloseViewButton: View {
#Environment(\.presentationMode) var presentationMode
var body: some View {
Button(action: {
presentationMode.wrappedValue.dismiss()
}) {
Text("Close the view")
}
}
}
Tested with Xcode 12.1 / iOS 14.1
I want to achieve the function. Like, "Look up" view that is from Apple.
My aim is when the sheet view push another view by navigation, the user can tap the navigation item button to close the sheet view. Like, this below gif.
I try to achieve this function.
I found a problem that is when the user tap the "Done" button. The App doesn't close the sheet view. It only pop the view to parent view. Like, this below gif.
This is my code.
import SwiftUI
struct ContentView: View {
#State var isShowSheet = false
var body: some View {
Button(action: {
self.isShowSheet.toggle()
}) {
Text("Tap to show the sheet")
}.sheet(isPresented: $isShowSheet) {
NavView()
}
}
}
struct NavView: View {
var body: some View {
NavigationView {
NavigationLink(destination: NavSubView()) {
Text("Enter Sub View")
}
} .navigationViewStyle(StackNavigationViewStyle())
}
}
struct NavSubView: View {
#Environment(\.presentationMode) var presentationMode
var body: some View {
Text("Hello")
.navigationBarItems(trailing:
Button(action: {
self.presentationMode.wrappedValue.dismiss()
}){
Text("Done")
}
)
}
}
How did I achieve this function? :)
Please help me, thank you. :)
UPDATE: Restored original version - provided below changes should be done, as intended, to the topic starter's code. Tested as worked with Xcode 13 / iOS 15
As navigation in sheet might be long enough and closing can be not in all navigation subviews, I prefer to use environment to have ability to specify closing feature only in needed places instead of passing binding via all navigation stack.
Here is possible approach (tested with Xcode 11.2 / iOS 13.2)
Define environment key to store sheet state
struct ShowingSheetKey: EnvironmentKey {
static let defaultValue: Binding<Bool>? = nil
}
extension EnvironmentValues {
var showingSheet: Binding<Bool>? {
get { self[ShowingSheetKey.self] }
set { self[ShowingSheetKey.self] = newValue }
}
}
Set this environment value to root of sheet content, so it will be available in any subview when declared
}.sheet(isPresented: $isShowSheet) {
NavView()
.environment(\.showingSheet, self.$isShowSheet)
}
Declare & use environment value only in subview where it is going to be used
struct NavSubView: View {
#Environment(\.showingSheet) var showingSheet
var body: some View {
Text("Hello")
.navigationBarItems(trailing:
Button("Done") {
self.showingSheet?.wrappedValue = false
}
)
}
}
I haven't tried SwiftUI ever, but I came from UIKit + RxSwift, so I kinda know how binding works. I read quite a bit of sample codes from a SwiftUI Tutorial, and the way you dismiss a modal is actually correct, but apparently not for a navigation stack.
One way I learned just now is use a #Binding var. This might not be the best solution, but it worked!
So you have this $isShowSheet in your ContentView. Pass that object to your NavView struct by declaring a variable in that NavView.
ContentView
.....
}.sheet(isPresented: $isShowSheet) {
NavView(isShowSheet: self.$isShowSheet)
}
NavView
struct NavView: View {
#Binding var isShowSheet: Bool
var body: some View {
NavigationView {
NavigationLink(destination: NavSubView(isShowSheet: self.$isShowSheet)) {
Text("Enter Sub View")
}
} .navigationViewStyle(StackNavigationViewStyle())
}
}
and finally, do the same thing to your subView.
NavSubView
struct NavSubView: View {
#Environment(\.presentationMode) var presentationMode
#Binding var isShowSheet: Bool
var body: some View {
Text("Hello")
.navigationBarItems(trailing:
Button(action: {
//self.presentationMode.projectedValue.wrappedValue.dismiss()
self.isShowSheet = false
}){
Text("Done")
}
)
}
}
Now as you can see, you just need to send a new signal to that isShowSheet binding var - false.
self.isShowSheet = false
Voila!
Here's an improved version of Asperi's code from above since they won't accept my edit. Main credit goes to them.
As navigation in sheet might be long enough and closing can be not in all navigation subviews, I prefer to use environment to have ability to specify closing feature only in needed places instead of passing binding via all navigation stack.
Here is possible approach (tested with Xcode 13 / iOS 15)
Define environment key to store sheet state
struct ShowingSheetKey: EnvironmentKey {
static let defaultValue: Binding<Bool>? = nil
}
extension EnvironmentValues {
var isShowingSheet: Binding<Bool>? {
get { self[ShowingSheetKey.self] }
set { self[ShowingSheetKey.self] = newValue }
}
}
Set this environment value to root of sheet content, so it will be available in any subview when declared
#State var isShowingSheet = false
...
Button("open sheet") {
isShowingSheet?.wrappedValue = true
}
// note no $ in front of isShowingSheet
.sheet(isPresented: isShowingSheet ?? .constant(false)) {
NavView()
.environment(\.isShowingSheet, self.$isShowingSheet)
}
Declare & use environment value only in subview where it is going to be used
struct NavSubView: View {
#Environment(\.isShowingSheet) var isShowingSheet
var body: some View {
Text("Hello")
.navigationBarItems(trailing:
Button("Done") {
isShowingSheet?.wrappedValue = false
}
)
}
}
I was surprised that whenever I tap on the button embedded in PresentationLink, the same view reference shows up all the time. What I mean is that we don't create another instance of the view.
This makes sense as the destination object is created within the body property and will therefore not be recreated unless a change occur.
Do you guys know if we have a trivial way to recreate a new view every time we hit the button? Or is it by design and should be use like this?
Thank you!
EDIT
After #dfd 's comment, it seems to be by designed.
Now how to handle this use case:
Let's say I present a NavigationView and I pushed one view. If I
dismiss and re present, I will go back on the view I previously
pushed. In this case, I believe it's wrong as I'd like the user to go
through the complete flow every single time. How can I make sure that
I go back on the first screen everytime?
Thank you (again)!
EDIT 2
Here's some code:
struct PresenterExample : View {
var body: some View {
VStack {
PresentationLink(destination: CandidateCreateProfileJobView()) {
Text("Present")
}
}
}
}
struct StackFirstView : View {
var body: some View {
NavigationLink(destination: StackSecondView()) {
Text("Got to view 2")
}
}
}
struct StackSecondView : View {
var body: some View {
Text("View 2")
}
}
In this case that would be PresenterExample presents StackFirstView which will push StackSecondView from the NavigationLink.
From there, let's say the user swipe down and therefore dismiss the presentation. When it clicks back on the PresentationLink in PresenterExample it will open back on StackSecondView, which is not what I want. I want to display StackFirstView again.
Makes more sense? :)
First Try: Failure
I tried using the id modifier to tell SwiftUI to treat each presentation of StackFirstView as a completely new view unrelated to prior views:
import SwiftUI
struct PresenterExample : View {
var body: some View {
VStack {
PresentationLink("Present", destination:
StackFirstView()
.onDisappear {
print("onDisappear")
self.presentationCount += 1
}
)
}
}
#State private var presentationCount = 0
}
struct StackFirstView : View {
var body: some View {
NavigationView {
NavigationLink(destination: StackSecondView()) {
Text("Go to view 2")
}.navigationBarTitle("StackFirstView")
}
}
}
struct StackSecondView : View {
var body: some View {
Text("View 2")
.navigationBarTitle("StackSecondView")
}
}
import PlaygroundSupport
PlaygroundPage.current.liveView = UIHostingController(rootView: PresenterExample())
This should do the following:
It should identify the StackFirstView by presentationCount. SwiftUI should consider each StackFirstView with a different identifier to be a completely different view. I've used this successfully with animated transitions.
It should increment presentationCount when the StackFirstView is dismissed, so that the next StackFirstView gets a different identifier.
The problem is that SwiftUI never calls the onDisappear closure for the presented view or any of its subviews. I'm pretty sure this is a SwiftUI bug (as of Xcode 11 beta 3). I filed FB6687752.
Second Try: FailureSuccess
Next I tried managing the presentation myself, using the presentation(Modal?) modifier, so I wouldn't need the onDisappear modifier:
import SwiftUI
struct PresenterExample : View {
var body: some View {
VStack {
Button("Present") {
self.presentModal()
}.presentation(modal)
}
}
#State private var shouldPresent = false
#State private var presentationCount = 0
private func presentModal() {
presentationCount += 1
shouldPresent = true
}
private var modal: Modal? {
guard shouldPresent else { return nil }
return Modal(StackFirstView().id(presentationCount), onDismiss: { self.shouldPresent = false })
}
}
struct StackFirstView : View {
var body: some View {
NavigationView {
NavigationLink(destination: StackSecondView()) {
Text("Go to view 2")
}.navigationBarTitle("StackFirstView")
}
}
}
struct StackSecondView : View {
var body: some View {
Text("View 2")
}
}
import PlaygroundSupport
PlaygroundPage.current.liveView = UIHostingController(rootView: PresenterExample())
This fails in a different way. The second and later presentations of StackFirstView simply present a blank view instead. Again, I'm pretty sure this is a SwiftUI bug. I filed FB6687804.
I tried passing the presentationCount down to StackFirstView and then applying the .id(presentationCount) modifier to the NavigationView's content. That crashes the playground if the modal is dismissed and presented again while showing StackSecondView. I filed FB6687850.
Update
This tweet from Ryan Ashcraft showed me a workaround that gets this second attempt working. It wraps the Modal's content in a Group, and applies the id modifier to the Group's content:
import SwiftUI
struct PresenterExample : View {
var body: some View {
VStack {
Button("Present") {
self.presentModal()
}.presentation(modal)
}
}
#State private var shouldPresent = false
#State private var presentationCount = 0
private func presentModal() {
presentationCount += 1
shouldPresent = true
}
private var modal: Modal? {
guard shouldPresent else { return nil }
return Modal(Group { StackFirstView().id(presentationCount) }, onDismiss: { self.shouldPresent = false })
}
}
struct StackFirstView : View {
var body: some View {
NavigationView {
NavigationLink(destination: StackSecondView()) {
Text("Go to view 2")
}.navigationBarTitle("StackFirstView")
}
}
}
struct StackSecondView : View {
var body: some View {
Text("View 2")
}
}
import PlaygroundSupport
PlaygroundPage.current.liveView = UIHostingController(rootView: PresenterExample())
This revised second try successfully resets the state of the Modal on each presentation. Note that the id must be applied to the content of the Group, not to the Group itself, to work around the SwiftUI bug.
Third Try: Success
I modified the second try so that, instead of using the id modifier, it wraps the StackFirstView inside a ZStack when presentationCount is an odd number.
import SwiftUI
struct PresenterExample : View {
var body: some View {
VStack {
Button("Present") {
self.presentModal()
}.presentation(modal)
}
}
#State private var shouldPresent = false
#State private var presentationCount = 0
private func presentModal() {
presentationCount += 1
shouldPresent = true
}
private var modal: Modal? {
guard shouldPresent else { return nil }
if presentationCount.isMultiple(of: 2) {
return Modal(presentationContent, onDismiss: { self.shouldPresent = false })
} else {
return Modal(ZStack { presentationContent }, onDismiss: { self.shouldPresent = false })
}
}
private var presentationContent: some View {
StackFirstView()
}
}
struct StackFirstView : View {
var body: some View {
NavigationView {
NavigationLink(destination: StackSecondView()) {
Text("Go to view 2")
}.navigationBarTitle("StackFirstView")
}
}
}
struct StackSecondView : View {
var body: some View {
Text("View 2")
}
}
import PlaygroundSupport
PlaygroundPage.current.liveView = UIHostingController(rootView: PresenterExample())
This works. I guess SwiftUI sees that the modal's content is a different type each time (StackFirstView vs. ZStack<StackFirstView>) and that is sufficient to convince it that these are unrelated views, so it throws away the prior presented view instead of reusing it.