How to bind to data that's part of an optional in SwiftUI - swiftui

Question

I'm curious, how do we specify a binding to State data that is part of an optional? For instance:
struct NameRecord {
var name = ""
var isFunny = false
}
class AppData: ObservableObject {
#Published var nameRecord: NameRecord?
}
struct NameView: View {
#StateObject var appData = AppData()
var body: some View {
Form {
if appData.nameRecord != nil {
// At this point, I *know* that nameRecord is not nil, so
// I should be able to bind to it.
TextField("Name", text: $appData.nameRecord.name)
Toggle("Is Funny", isOn: $appData.nameRecord.isFunny)
} else {
// So far as I can tell, this should never happen, but
// if it does, I will catch it in development, when
// I see the error message in the constant binding.
TextField("Name", text: .constant("ERROR: Data is incomplete!"))
Toggle("Is Funny", isOn: .constant(false))
}
}
.onAppear {
appData.nameRecord = NameRecord(name: "John")
}
}
}
I can certainly see that I'm missing something. Xcode gives errors like Value of optional type 'NameRecord?' must be unwrapped to refer to member 'name' of wrapped base type 'NameRecord') and offers some FixIts that don't help.
Based on the answer from the user "workingdog support Ukraine" I now know how to make a binding to the part I need, but the solution doesn't scale well for a record that has many fields of different type.
Given that the optional part is in the middle of appData.nameRecord.name, it seems that there might be a solution that does something like what the following function in the SwiftUI header might be doing:
public subscript<Subject>(dynamicMember keyPath: WritableKeyPath<Value, Subject>) -> Binding<Subject> { get }
My SwiftFu is insufficient, so I don't know how this works, but I suspect it's what is doing the work for something like $appData.nameRecord.name when nameRecord is not an optional. I would like to have something where this function would result in a binding to .constant when anything in the keyPath is nil (or even if it did a fatalError that I would avoid with conditionals as above). It would be great if there was a way to get a solution that was as elegant as Jonathan's answer that was also suggested by workingdog for a similar situation. Any pointers in that area would be much appreciated!

Answer 1

Binding has a failable initializer that transforms a Binding<Value?>.
if let nameRecord = Binding($appData.nameRecord) {
TextField("Name", text: nameRecord.name)
Toggle("Is Funny", isOn: nameRecord.isFunny)
} else {
Text("Data is incomplete")
TextField("Name", text: .constant(""))
Toggle("Is Funny", isOn: .constant(false))
}
Or, with less repetition:
if appData.nameRecord == nil {
Text("Data is incomplete")
}
let bindings = Binding($appData.nameRecord).map { nameRecord in
( name: nameRecord.name,
isFunny: nameRecord.isFunny
)
} ?? (
name: .constant(""),
isFunny: .constant(false)
)
TextField("Name", text: bindings.name)
Toggle("Is Funny", isOn: bindings.isFunny)