SwiftUI Picker selection parameter giving "Expression type 'Binding<_>' is ambiguous without more context" error

Question

I'm getting a Expression type 'Binding<_>' is ambiguous without more context error at $order.quantity.contracts in the following code:

struct ContractsPickerView: View {
    @Binding var order: Order
    
    var question: String
            
    var body: some View {
                         
                        Error
                          |
                          |
                          V                
        Picker(selection: $order.quantity.contracts, label: Text("\(question)").font(.headline)) { 
            ForEach(0..<101, id: \.self) { contracts in
                Text("\(contracts)")
            }
        }
    }
}

In fact, Xcode is not offering me the contracts attribute in the Quantity class after typing $order.quantity.. Here are the models:

struct Order {
    var quantity: Quantity?
}

struct Quantity: Hashable {
    private var userEnteredContracts: Int?
    var contracts: Int {
        get {
            return userEnteredContracts
        }
        set(newContracts) {
            userEnteredContracts = newContracts
        }
    }
}

Can somebody explain the issue and offer a solution please?

Answer 1

For your binding to work quantity can't be nil.

In reality instead of:

$order.quantity.contracts

you're trying to do

$order.quantity?.contracts

which is not allowed. How should your Picker behave if quantity is nil?

A solution may be to make quantity non-optional:

struct Order {
    var quantity: Quantity
}

---

Also note that your code will not compile: contracts are of type Int but you return userEnteredContracts which are of type Int?

You may want to make contracts optional:

struct Quantity: Hashable {
    private var userEnteredContracts: Int?
    var contracts: Int? {
        get {
            return userEnteredContracts
        }
        set(newContracts) {
            userEnteredContracts = newContracts
        }
    }
}

or provide a default value:

struct Quantity: Hashable {
    private var userEnteredContracts: Int?
    var contracts: Int {
        get {
            return userEnteredContracts ?? 0
        }
        set(newContracts) {
            userEnteredContracts = newContracts
        }
    }
}