.sheet in SwiftUI strange behaviour when passing a variable - ios

Question

I am using .sheet view in SwiftUI and I am observing a strange behavior in the execution of the code.
I am having a view SignInView2:
struct SignInView2: View {
#Environment(\.presentationMode) var presentationMode
#State var invitationUrl = URL(string: "www")
#State private var showingSheet = false
var body: some View {
VStack {
Text("Share Screen")
Button(action: {
print("link: \(invitationUrl)") // Here I see the new value assigned from createLink()
self.showingSheet = true
}) {
Text("Share")
}
.sheet(isPresented: $showingSheet) {
let invitationLink = invitationUrl?.absoluteString // Paasing the old value (www)
ActivityView(activityItems: [NSURL(string: invitationLink!)] as [Any], applicationActivities: nil)
}
}
.onAppear() {
createLink()
}
}
}
which calls create a link method when it appears:
extension SignInView2 {
func createLink() {
guard let uid = Auth.auth().currentUser?.uid else {
print("tuk0")
return }
let link = URL(string: "https://www.example.com/?invitedby=\(uid)")
print("tuk1:\(String(describing: link))")
let referralLink = DynamicLinkComponents(link: link!, domainURIPrefix: "https://makeitso.page.link")
print("tuk2:\(String(describing: referralLink))")
referralLink?.iOSParameters = DynamicLinkIOSParameters(bundleID: "com.IVANDOS.ToDoFirebase")
referralLink?.iOSParameters?.minimumAppVersion = "1.0"
referralLink?.iOSParameters?.appStoreID = "13129650"
referralLink?.shorten { (shortURL, warnings, error) in
if let error = error {
print(error.localizedDescription)
return
}
print("tuk4: \(shortURL)")
self.invitationUrl = shortURL!
}
}
}
That method assigns a value to the invitationUrl variable, which is passed to the sheet. Unfortunatelly, when the sheet appears, I don't see the newly assigned variable but I see only "www". Can you explain me how to pass the new value generated from createLink()?

Answer 1

This is known behaviour of sheet since SwiftUI 2.0. Content is created in time of sheet created not in time of showing. So the solution can be either to use .sheet(item:... modifier or passing binding in sheet content view (which is kind of reference to state storage and don't need to be updated).
Here is a demo of possible approach. Prepared with Xcode 12.4.
struct SignInView2: View {
#Environment(\.presentationMode) var presentationMode
#State private var invitationUrl: URL? // by default is absent
var body: some View {
VStack {
Text("Share Screen")
Button(action: {
print("link: \(invitationUrl)")
self.invitationUrl = createLink() // assignment activates sheet
}) {
Text("Share")
}
.sheet(item: $invitationUrl) {
ActivityView(activityItems: [$0] as [Any], applicationActivities: nil)
}
}
}
}
// Needed to be used as sheet item
extension URL: Identifiable {
public var id: String { self.absoluteString }
}