I would like to start by highlighting my views hierarchy. I just have FindUserView
and WelcomeView
.
FindUserView
is used for retrieving users from the server if the entered email exists. If so, then it automatically redirects me to the next WelcomeView
where I can enter password and login.
I've created a repo here and a video SwiftUI - Pop back does not deallocate view
My FindUserView
: ---------------------------- and WelcomeView
:
By pressing NEXT button on FindUserView
I fetch a user from the database:
func fetchUser(with email: String) {
userService.getUser(with: email) { (result) in
switch result {
case .success(_):
self.showActivityIndicator = false
self.showingAlert = false
self.showWelcomeView = true
break
case .failure:
self.showingAlert = true
break
}
}
}
I use NavigationView
and programatically show WelcomeView
by changing showWelcomeView
state above:
NavigationLink(destination: WelcomeView(), isActive: $showWelcomeView) { EmptyView() }
Now I am on welcome view WelcomeView
.
But when I press this button and pop back, my WelcomeView
still exists.
As I use @EnvironmentObject
with observable property state I see how it reflects to the view which is already dismissed. Is this correct behaviour? Or do I need to dealloc WelcomeView
somehow? Does it lead to memory leaks?
I am a bit worry as in UIKit
when you pop back in navigation stack the view controller it is deallocated by UINavigationController
by removing view controller from the array automatically. How to pop back correctly in SwiftUI?
Actually it is not clear if it is defect or not - SwiftUI views are values, so there is no dealloc thing for them. It looks like NavigationView
just keeps something like lastView variable until it is replaced with another one. Maybe worth submitting feedback to Apple.
Meanwhile here is solution that allows to defer real destination view creation until exactly NavigationLink
tapped and cleanup it (w/ any related resources, like view model) when view is removed from stack by Back button.
Tested with Xcode 11.4 / iOS 13.4
Helper proxy view presenter:
struct LinkPresenter<Content: View>: View {
let content: () -> Content
@State private var invlidated = false
init(@ViewBuilder _ content: @escaping () -> Content) {
self.content = content
}
var body: some View {
Group {
if self.invlidated {
EmptyView()
} else {
content()
}
}
.onDisappear { self.invlidated = true }
}
}
Usage:
NavigationLink(destination: LinkPresenter { WelcomeView() },
isActive: $showWelcomeView) { EmptyView() }