The problem

TL;DR: A String I'm trying to bind to inside TextField is nested in an Optional type, therefore I cannot do that in a straightforward manner. I've tried various fixes listed below.

I'm a simple man and my use case is rather simple - I want to be able to use TextField to edit my object's name.
The difficulty arises due to the fact that the object might not exist.

The code

Stripping the code bare, the code looks like this.
Please note that that the example View does not take Optional into account

model

struct Foo {
  var name: String
}

extension Foo {
  var sampleData: [Foo] = [
    Foo(name: "Bar")
  ]
}

view

again, in the perfect world without Optionals it would look like this

struct Ashwagandha: View {
  @StateObject var ashwagandhaVM = AshwagandhaVM()
  var body: some View {
    TextField("", text: $ashwagandhaVM.currentFoo.name)
  }
}

view model

I'm purposely not unwrapping the optional, making the currentFoo: Foo?

class AshwagandhaVM: ObservableObject {
  @Published var currentFoo: Foo?

  init() {
    self.currentFoo = Foo.sampleData.first
  }
}

The trial and error

Below are the futile undertakings to make the TextField and Foo.name friends, with associated errors.

Optional chaining

The 'Xcode fix' way

TextField("", text: $ashwagandhaVM.currentFoo?.name)
gets into the cycle of fixes on adding/removing "?"/"!"

The desperate way

TextField("Change chatBot's name", text: $(ashwagandhaVM.currentFoo!.name)
"'$' is not an identifier; use backticks to escape it"

Forced unwrapping

The dumb way

TextField("", text: $ashwagandhaVM.currentFoo!.name)
"Cannot force unwrap value of non-optional type 'Binding<Foo?>'"

The smarter way

if let asparagus = ashwagandhaVM.currentFoo.name {
  TextField("", text: $asparagus.name)
}

"Cannot find $asparagus in scope"

Workarounds

class AshwagandhaVM: ObservableObject {
    @Published var currentFoo: Foo?

    init() {
        self.currentFoo = Foo.sampleData.first
    }
    func saveCurrentName(_ name: String) {
        if currentFoo == nil {
            Foo.sampleData.append(Foo(name: name))
            self.currentFoo = Foo.sampleData.first(where: {$0.name == name})
        }
        else {
            self.currentFoo?.name = name
        }
    }
}

struct ContentView: View {
    @StateObject var ashwagandhaVM = AshwagandhaVM()
    @State private var textInput = ""
    @State private var showingConfirmation = false
    
    var body: some View {
        VStack {
            TextField("", text: $textInput)
                .padding()
                .textFieldStyle(.roundedBorder)
            Button("save") {
                showingConfirmation = true
            }
            .padding()
            .buttonStyle(.bordered)
            .controlSize(.large)
            .tint(.green)
            .confirmationDialog("are you sure?", isPresented: $showingConfirmation, titleVisibility: .visible) {
                Button("Yes") {
                    confirmAndSave()
                }
                Button("No", role: .cancel) { }
            }
            //just to check
            if let name = ashwagandhaVM.currentFoo?.name {
                Text("in model: \(name)")
                    .font(.largeTitle)
            }
        }
        .onAppear() {
            textInput = ashwagandhaVM.currentFoo?.name ?? "default"
        }
    }
    
    func confirmAndSave() {
        ashwagandhaVM.saveCurrentName(textInput)
    }
}

UPDATE

do it with whole struct

struct ContentView: View {
    @StateObject var ashwagandhaVM = AshwagandhaVM()
    @State private var modelInput = Foo(name: "input")
    @State private var showingConfirmation = false
    
    var body: some View {
        VStack {
            TextField("", text: $modelInput.name)
                .padding()
                .textFieldStyle(.roundedBorder)
            Button("save") {
                showingConfirmation = true
            }
            .padding()
            .buttonStyle(.bordered)
            .controlSize(.large)
            .tint(.green)
            .confirmationDialog("are you sure?", isPresented: $showingConfirmation, titleVisibility: .visible) {
                Button("Yes") {
                    confirmAndSave()
                }
                Button("No", role: .cancel) { }
            }
            //just to check
            if let name = ashwagandhaVM.currentFoo?.name {
                Text("in model: \(name)")
                    .font(.largeTitle)
            }
        }
        .onAppear() {
            modelInput = ashwagandhaVM.currentFoo ?? Foo(name: "input")
        }
    }
    
    func confirmAndSave() {
        ashwagandhaVM.saveCurrentName(modelInput.name)
    }
}

CodePudding user response：

There is a handy Binding constructor that converts an optional binding to non-optional, use as follows:

struct ContentView: View {
   @StateObject var store = Store()

   var body: some View {
    if let nonOptionalStructBinding = Binding($store.optionalStruct) {
        TextField("Name", text: nonOptionalStructBinding.name)
    }
    else {
        Text("optionalStruct is nil")
    }
  }
}

Also, MVVM in SwiftUI is a bad idea because the View data struct is better than a view model object.