Generic parameter 'SelectionValue' could not be inferred

@lvandal

Jul '20

Hi! What is wrong with this code and why does this work for a Picker but not a List?

struct ContentView: View {
    enum FooBar: CaseIterable, Identifiable {
        public var id : String { UUID().uuidString }

        case foo
        case bar
        case buzz
        case bizz
    }

    @State var selectedFooBar: FooBar = .bar

    var body: some View {
        VStack {
            Picker("Select", selection: $selectedFooBar) {
                ForEach(FooBar.allCases) { item in
                    Text(self.string(from: item)).tag(item)
                }
            }

            List(FooBar.allCases, selection: $selectedFooBar) { item in // Generic parameter 'SelectionValue' could not be inferred
                Text(self.string(from: item)).tag(item)
            }

            Text("You selected: \(self.string(from: selectedFooBar))")
        }
    }

    private func string(from item: FooBar) -> String {
        var str = ""

        switch item {
        case .foo:
            str = "Foo"

        case .bar:
            str = "Bar"

        case .buzz:
            str = "Buzz"

        case .bizz:
            str = "Bizz"
        }
        return str
    }
}

3

@danieleprice1

Jul '20

Your syntax for List is incorrect. Try this:

List(FooBar.allCases, id:\.self) { item in
     Text(self.string(from: item)).tag(item)
}

or this is how I would write it:

List{
   ForEach(FooBar.allCases) { item in
        Text(self.string(from: item)).tag(item)
   }
}

3

@lvandal

Jul '20

While this compiles, it does not allow to bind selectedFooBar.

3

@danieleprice1

Jul '20

Sorry, I must have misunderstood. What are you trying to do with the list? You can't select an item in a List.

You could add a button in each cell in the list...

List{
   ForEach(FooBar.allCases) { item in
      HStack{
           Text(self.string(from: item))
             .foregroundColor(item == self.selectedFooBar ? Color.green : Color(UIColor.label))
           Spacer()

           Button(action: {
               self.selectedFooBar = item
            }){
                  Text("Push")
                }
       }
    }
}

3

@lvandal

Jul '20

I did go with the Buttons solution but wasn't sure if that was the proper solution. Thanks!

3

@jfranknichols

Aug '20

I posted the same question a couple days ago.

If you can not select a row in a list, then why have the "selection" available in the syntax? Is it for setting the item and not for determining the selection?

If so, then how would I impliment the ability to select a row and add a child to it? Adding a button to every item in a list seems kind of clunky.

TIA

3

@nigelhamilton HWS+

Aug '20

I have similar code in a mac app which allows list item to be selected. Mine uses a ForEach though :

 List(selection: $selectedFontType, content: {
                    ForEach(fontTypes, id:\.self) {
                        Text($0)
                    }
                })

3

	@lvandal Jul '20 Hi! What is wrong with this code and why does this work for a Picker but not a List? struct ContentView: View { enum FooBar: CaseIterable, Identifiable { public var id : String { UUID().uuidString } case foo case bar case buzz case bizz } @State var selectedFooBar: FooBar = .bar var body: some View { VStack { Picker("Select", selection: $selectedFooBar) { ForEach(FooBar.allCases) { item in Text(self.string(from: item)).tag(item) } } List(FooBar.allCases, selection: $selectedFooBar) { item in // Generic parameter 'SelectionValue' could not be inferred Text(self.string(from: item)).tag(item) } Text("You selected: \(self.string(from: selectedFooBar))") } } private func string(from item: FooBar) -> String { var str = "" switch item { case .foo: str = "Foo" case .bar: str = "Bar" case .buzz: str = "Buzz" case .bizz: str = "Bizz" } return str } } 3
	@danieleprice1 Jul '20 Your syntax for List is incorrect. Try this: `List(FooBar.allCases, id:\.self) { item in Text(self.string(from: item)).tag(item) }` or this is how I would write it: `List{ ForEach(FooBar.allCases) { item in Text(self.string(from: item)).tag(item) } }` 3
	@lvandal Jul '20 While this compiles, it does not allow to bind selectedFooBar. 3
	@danieleprice1 Jul '20 Sorry, I must have misunderstood. What are you trying to do with the list? You can't select an item in a List. You could add a button in each cell in the list... `List{ ForEach(FooBar.allCases) { item in HStack{ Text(self.string(from: item)) .foregroundColor(item == self.selectedFooBar ? Color.green : Color(UIColor.label)) Spacer() Button(action: { self.selectedFooBar = item }){ Text("Push") } } } }` 3
	@lvandal Jul '20 I did go with the Buttons solution but wasn't sure if that was the proper solution. Thanks! 3
	@jfranknichols Aug '20 I posted the same question a couple days ago. If you can not select a row in a list, then why have the "selection" available in the syntax? Is it for setting the item and not for determining the selection? If so, then how would I impliment the ability to select a row and add a child to it? Adding a button to every item in a list seems kind of clunky. TIA 3
	@nigelhamilton HWS+ Aug '20 I have similar code in a mac app which allows list item to be selected. Mine uses a ForEach though : `List(selection: $selectedFontType, content: { ForEach(fontTypes, id:\.self) { Text($0) } })` 3

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