PresentationLink always use the same destination object - ios

Question

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? :)

Answer 1

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.