SwiftUI 字符串符合 Identifiable 似乎不正确

Question

I am using an array in a List , in the List there's a ForEach , like:

struct AView: View {

    @State var foo: [String] = ["a", "b", "c"]

    var body: some View {
        ZStack {
            Color.white
            List {
                ForEach(foo.indices) { index in
                    Text(foo[index])
                }
            }
        }

    }
}

This works well, then I want to add a button to insert new items:

   List {
            ForEach(foo.indices) { index in
                Text(foo[index])
            }
        }
        Button("Add") {
            foo.append("foo")
        }
    }

Then I got the error, which is obviously:

ForEach<Range<Int>, Int, Text> count (4) != its initial count (3). `ForEach(_:content:)` should only be used for *constant* data. Instead conform data to `Identifiable` or use `ForEach(_:id:content:)` and provide an explicit `id`!

Here mentioned

Identifiable or use ForEach(_:id:content:)

I can use ForEach(foo.indices, id:\\.self) which solved the issue.

I also want to try Identifiable , and don't use id:\\.self in the ForEach , ForEach(foo.indices) .

I added extension to String like:

extension String: Identifiable {
    public var id: String { self }
}

But still got the same issue. Any thing I miss-understood? thanks!

EDIT

According to the comment @New Dev, as I literal indices , so I added extension to Int :

extension Int: Identifiable {
    public var id: Int { self }
}

still doesn't work.

Answer 1

ForEach has multiple init overloads.

init(Range<Int>, content: (Int) -> Content) only works with a constant range - hence the error.

init(Data, content: (Data.Element) -> Content) requires Data to conform to RandomAccessCollection of Identifiable elements. That's the one you want to use.

The problem is that your RandomAccessCollection (to which Range<Int> conforms) is a collection of Int elements.

Though you can conform Int to Identifiable , this would still not work. It would still use the first ForEach.init with a Range<Int> parameter, because of method overload preference - ie Range<Int> matches the more specific init with Range<Int> parameter, rather than the less specific init with RandomAccessCollection .

---

So, your choices are:

1. Use the third init(Data, id: KeyPath<Data.Element, ID>, content: (Data.Element) -> Content) by explicitly specifying the id .

ForEach(foo.indices, id:\.self) { index in 
}

2. Convert to Array<Int> and conform Int: Identifiable :

extension Int: Identifiable { var id: Self { self } }

ForEach(Array(foo.indices)) { index in 
}