data-bindingswiftuinavigationlink

SwiftUI update data for parent NavigationView


how can I update data in TextField that lives in the detail of a NavigationView? I want the data to be updated in the List of the parent View. Here is my code:

class Address: ObservableObject, Identifiable {
    let id = UUID()
    @Published var name: String
    @Published var age: String
    
    init(name: String, age: String) {
        self.name = name
        self.age = age
    }
}
class AddressBook: ObservableObject {
    @Published var addresses: [Address]

    init(addresses: [Address]) {
        self.addresses = addresses
    }
}
struct TestData {
    static let addressbook = AddressBook(addresses: [
        Address(name: "Person1", age: "39"),
        Address(name: "Person2", age: "22")
    ])
}
struct ContentView: View {
    @ObservedObject var addressbook = TestData.addressbook
    
    var body: some View {
        NavigationView {
            List (addressbook.addresses) {address in
                NavigationLink(destination: AddressDetail(address: address)) {
                    Text(address.name)
                }
            }
            .navigationBarTitle("Addressbook")
        }
        
    }
}

struct AddressDetail: View {
    @ObservedObject var address: Address
    
    var body: some View {
        Form {
            TextField("name", text: $address.name)
            
            TextField("age", text: $address.age)
        }
        
    }
}

This code doesn't work: If I go to the AddressDetail-View, change the TextField values and then go back, the changes don't update in the List-View.

Nico


Solution

  • The problem is that Address is a class, so if its published properties changed the reference in addresses is not changed, but ContentView view observes addressbook as a container of addresses.

    Here is demo of possible approach (tested & works with Xcode 12b / iOS 14, also on 11.4 / iOS 13.4)

    List (addressbook.addresses) {address in
        NavigationLink(destination: AddressDetail(address: address)) {
            Text(address.name)
                .onReceive(address.objectWillChange) { _ in
                    self.addressbook.objectWillChange.send()
                }
        }
    }
    

    Alternate: based on Binding (requires much more changes, so, as for me, less preferable, but worth mention

    struct Address: Identifiable, Hashable {
        let id = UUID()
        var name: String
        var age: String
    
        init(name: String, age: String) {
            self.name = name
            self.age = age
        }
    }
    class AddressBook: ObservableObject {
        @Published var addresses: [Address]
    
        init(addresses: [Address]) {
            self.addresses = addresses
        }
    }
    struct TestData {
        static let addressbook = AddressBook(addresses: [
            Address(name: "Person1", age: "39"),
            Address(name: "Person2", age: "22")
        ])
    }
    
    struct ContentView: View {
        @ObservedObject var addressbook = TestData.addressbook
    
        var body: some View {
            NavigationView {
                List (Array(addressbook.addresses.enumerated()), id: \.element) { i, address in
                    NavigationLink(destination: AddressDetail(address: self.$addressbook.addresses[i])) {
                        Text(address.name)
                    }
                }
                .navigationBarTitle("Addressbook")
            }
    
        }
    }
    
    struct AddressDetail: View {
        @Binding var address: Address
    
        @State private var name: String
        @State private var age: String
    
        init(address: Binding<Address>) {
            _address = address
            _name = State(initialValue: _address.wrappedValue.name)
            _age = State(initialValue: _address.wrappedValue.age)
        }
        var body: some View {
            Form {
                TextField("name", text: $name)
    
                TextField("age", text: $age)
            }
            .onDisappear {
                self.address.name = self.name
                self.address.age = self.age
            }
        }
    }