Passing binding back to parent's parent view - ios

Question

I have 4 views.
Grandparent
Parent
Child
EditView
Grandparent has a navigation link to Parent, and Parent a navigation link to Child. Child has a button which initializes a #State variable, location (a class), from Grandparent, via a binding in Parent and a binding in Child. That same button also updates a #State variable, showEditView, from Grandparent (via bindings again), which shows the EditView.
There are 11 lines which are currently commented out. If they are commented out, the app throws a "Fatal error: Unexpectedly found nil..." error when I tap the button in the Child view. If either section is uncommented, the button does not throw an error.
It also works if I pass the bound location to the EditView, not property itself like I'm currently doing, where it is then wrapped as an #ObservedObject.
I don't understand what is going on here. The only thing I can of is that, when it's working, SwiftUI is updating the location property because it's used in the body. If that is the case, that seems to indicate that I have to include a hidden Text view of this property every time I want to do have properties passed around this way.
Grandparent
import SwiftUI
struct Grandparent: View {
#State var location: Location!
#State var showEditView: Bool = false
var body: some View {
NavigationView {
VStack{
NavigationLink(
destination: Parent(location: $location, showEditView: $showEditView)) {
Text("Navigate")
}
// // section 1
// if location != nil {
// Text(location.name)
// } else {
// Text("No location yet")
// }
}
// // section 2
// .navigationBarItems(trailing:
// Button("Edit"){
// showEditView = true
// }
// .disabled(location == nil)
// )
}
.padding()
.sheet(isPresented: $showEditView) {
EditView(placemark: location, dismiss: { showEditView = false })
}
}
}
Parent
import SwiftUI
struct Parent: View {
#Binding var location: Location!
#Binding var showEditView: Bool
var body: some View {
NavigationLink(
destination: Child(location: $location, showEditView: $showEditView),
label: {
Text("Child")
})
}
}
Child
import SwiftUI
struct Child: View {
#Binding var location: Location!
#Binding var showEditView: Bool
var body: some View {
Button("Make location") {
location = Location(name: "Lebanon")
showEditView = true
}
}
}
EditView
import SwiftUI
struct EditView: View {
#ObservedObject var placemark: Location
var dismiss: () -> Void
var body: some View {
NavigationView {
Text(placemark.name)
.navigationTitle("Edit place")
.navigationBarItems(trailing: Button("Done") { dismiss() })
}
}
}
Location
import Foundation
class Location: ObservableObject {
init(name: String) {
self.name = name
}
#Published var name: String
}

Answer 1

You probably shouldn't declare your Location as ! and then do nil checking on it. Using ! is sort of asking for a crash to happen. I think what you're encountering is a the sheet getting rendered before location is set. There aren't any guarantees about when in the run loop a #State variable gets set, so it's better to account for scenarios where it is nil (and definitely not using ! to force unwrap it).
Secondly, at least given the scenario you have here, you probably shouldn't be using a class for Location -- it should just be a struct.
Eventually, you are going to run into a little bit of complexity, because judging by your View's name, you want to edit the Location at some point. This becomes a little more tricky with an Optional, since things like TextField want non-optional values, but this can be solved in various was (see where I used nonNilBinding).
Something like this is definitely a more safe approach than what you're currently doing. It may not be exactly what you want, but hopefully it can get you on the right path.
struct Location {
var name : String
}
struct Grandparent: View {
#State var location: Location?
#State var showEditView: Bool = false
var body: some View {
NavigationView {
VStack{
NavigationLink(
destination: Parent(location: $location, showEditView: $showEditView)) {
Text("Navigate")
}
if let location = location {
Text(location.name)
} else {
Text("No location yet")
}
}
.padding()
.sheet(isPresented: $showEditView) {
EditView(placemark: $location, dismiss: { showEditView = false })
}
}
}
}
struct Parent: View {
#Binding var location: Location?
#Binding var showEditView: Bool
var body: some View {
NavigationLink(
destination: Child(location: $location, showEditView: $showEditView),
label: {
Text("Child")
})
}
}
struct Child: View {
#Binding var location: Location?
#Binding var showEditView: Bool
var body: some View {
Button("Make location") {
location = Location(name: "Lebanon")
showEditView = true
}
}
}
struct EditView: View {
#Binding var placemark: Location?
var dismiss: () -> Void
var nonNilBinding : Binding<Location> {
.init { () -> Location in
placemark ?? Location(name:"Default")
} set: { (newValue) in
placemark = newValue
}
}
var body: some View {
NavigationView {
TextField("Name", text: nonNilBinding.name)
.navigationTitle("Edit place")
.navigationBarItems(trailing: Button("Done") { dismiss() })
}
}
}