Strange behavior of SwiftUI TextField (MacOS)

user_3527576 0
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I'm experiencing a strange behaviour of TextFields using SwiftUI on a MacOS application (XCode 11.0 stable, CoreData), probably due to some misconceptions on my side regarding SwiftUI dataflow.

Implementation

Please consider this basic Master/Detail View setup:

  • Model: Account
  • Container: ContentView
  • Master: AccountListView
  • Detail: AccountEditView
final class Account: NSManagedObject, Identifiable {
            @NSManaged var id: UUID
            @NSManaged var name: String
        }

struct ContentView: View {
    var body: some View {
        NavigationView {
            AccountListView()
                .listStyle(SidebarListStyle())
        }
        .navigationViewStyle(DoubleColumnNavigationViewStyle())
        .frame(minWidth: 300, idealWidth: nil, maxWidth: nil, minHeight: 300, idealHeight: nil, maxHeight: nil, alignment: .topLeading)
    }
}

struct AccountListView: View {

    @FetchRequest(entity: Account.entity(), sortDescriptors: [])
    var accounts: FetchedResults<Account>

    var body: some View {
        VStack {
            List(accounts) { account in
                NavigationLink (destination: AccountEditView(account: account)) {
                    Text(account.name)
                }
            }
        }
    }
}

struct AccountEditView: View {

    @ObservedObject var account: Account

    var body: some View {
        VStack {
            TextField("Account Name", text: $account.name)
            Spacer()
        }
    }
}

Issue

The views are populated correctly. Selecting an account in list view properly updates the textfield in detail view.

However as soon as I edit the textfield value, things go strange:

  • When the detail view is newly updated, the textfield loses focus after the first entered character. The account name in list view is properly updated (showing the single character entered)
  • When I'm entering the textfied again, I can type more characters without losing focus (again, the account name in the list view is update)
  • As soon as I press enter, the TextField's value restores to the old value, while the list view's value remains at the updated value.
  • When switching back and forth between different account entries, the detail view shows the correct values. So the model object was properly updated.

My questions:

  1. Why does the TextField lose focus when entering a single character for the first time
  2. Why does the TextField restore it's previous value (and not the model value) when commiting the change

Sorry for the lengthy question...

swiftui swift
1 Answers

The coredata attributes are a different kind of optionals. So we need to define getter and setter inside the Model class to convert their behavior.

If your Entity's code gen is not manual/none, add this following code in contentview

extension Account {
    var wrappedName: String {
        get { name ?? "Unknown"}
        set { name = newValue }
    }
}

then replace all the account.name with account.wrappedName

P.S. This is tested and worked in XCode 11.4 on MacOS 10.5

user_23828130
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