Can't Use Dictionary to Store Picker selections?

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Created May ’20

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Note: If the Xcode canvas doesn't show anything in Live Preview, try an actual Simulator - no idea why canvas wasn't working in this demo but not important to the main issue.

I have a view with several pickers. Rather than flooding the namespace, I used an array storing the values. This works fine.

To improve it, I decided it would be more maintainable to use a dictionary, however, after making the switch, although there are no compile or runtime errors, it appears the picker's selection parameter isn't able to read or write to the dictionary?

struct ContentView: View {
    @State private var data = [ // <- doesn't appear to be used by picker 1
        "key1": 0,
        "key2": 5
    ]
    @State private var indices = [Int](repeating: 0, count: 2) // <- updates fine
    
    var body: some View {
        NavigationView {
            Form {
               // Picker 1, doesn't work
                Picker(selection: $data["key1"], label: Text("dict")) {
                    ForEach(0..<100) {
                        Text(String($0)) // <- shows no value
                    }
                }
               // Picker 2, works fine
                Picker(selection: $indices[0], label: Text("array")) {
                    ForEach(0..<100) {
                        Text(String($0))
                    }
                }
            }
        }
    }
}

Answered by Claude31 in 420093022

That's visibly a known issue:

https://stackoverflow.com/questions/60853197/binding-swiftui-picker-to-value-held-in-dictionary

For some reason, dictionaries does not seem suited to hold a picker selection…

Found this other SO, where they define a new binding. Is it a hint to a solution ?

https://stackoverflow.com/questions/57696082/swiftui-set-a-binding-from-the-string-result-of-a-picker

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Answer 1

Claude31 OP

May ’20

Accepted Answer

That's visibly a known issue:

https://stackoverflow.com/questions/60853197/binding-swiftui-picker-to-value-held-in-dictionary

For some reason, dictionaries does not seem suited to hold a picker selection…

Found this other SO, where they define a new binding. Is it a hint to a solution ?

https://stackoverflow.com/questions/57696082/swiftui-set-a-binding-from-the-string-result-of-a-picker

0

Answer 2

OOPer OP

May ’20

I'm not sure why SwiftUI does not work with Dictionay.

One possible reason may be something about Optionals, as `$data["key1"]` is of type `Binding<Int?>`.

Many of the Swift Standard Library's features prefer static type system, as found in Codable,

it might be more and more maintainable to use a struct.

struct ContentView: View {
    private struct PickerSelection {
        var key1: Int = 0
        var key2: Int = 5
    }
    @State private var selections = PickerSelection()
    
    @State private var indices = [Int](repeating: 0, count: 2) // <- updates fine
    
    var body: some View {
        NavigationView {
            Form {
                // Picker 1, does work
                Picker(selection: $selections.key1, label: Text("struct")) {
                    ForEach(0..<100) {
                        Text(String($0))
                    }
                }
                // Picker 2, works fine
                Picker(selection: $indices[0], label: Text("array")) {
                    ForEach(0..<100) {
                        Text(String($0))
                    }
                }
            }
        }
    }
}

0

Answer 3

thatNoseyParker OP

May ’20

Interestingly that post didn't come up with me googling efforts, maybe since it doesn't have any activity on it? Nevertheless, thanks for the reply.

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