SwiftUI - Automatically add dividers between each element of a `ForEach`-CodePudding

I'm using a ForEach to display the contents of an array, then manually showing a divider between each element by checking the element index. Here's my code:

struct ContentView: View {
    let animals = ["Apple", "Bear", "Cat", "Dog", "Elephant"]

    var body: some View {
        VStack {
            /// array of tuples containing each element's index and the element itself
            let enumerated = Array(zip(animals.indices, animals))
            ForEach(enumerated, id: \.1) { index, animal in
                Text(animal)

                /// add a divider if the element isn't the last
                if index != enumerated.count - 1 {
                    Divider()
                        .background(.blue)
                }
            }
        }
    }
}

Result:

This works, but I'd like a way to automatically add dividers everywhere without writing the Array(zip(animals.indices, animals)) every time. Here's what I have so far:

struct ForEachDividerView<Data, Content>: View where Data: RandomAccessCollection, Data.Element: Hashable, Content: View {
    var data: Data
    var content: (Data.Element) -> Content

    var body: some View {
        let enumerated = Array(zip(data.indices, data))
        ForEach(enumerated, id: \.1) { index, data in

            /// generate the view
            content(data)

            /// add a divider if the element isn't the last
            if let index = index as? Int, index != enumerated.count - 1 {
                Divider()
                    .background(.blue)
            }
        }
    }
}

/// usage
ForEachDividerView(data: animals) { animal in
    Text(animal)
}

This works great, isolating all the boilerplate zip code and still getting the same result. However, this is only because animals is an array of Strings, which conform to Hashable — if the elements in my array didn't conform to Hashable, it wouldn't work:

struct Person {
    var name: String
}

struct ContentView: View {
    let people: [Person] = [
        .init(name: "Anna"),
        .init(name: "Bob"),
        .init(name: "Chris")
    ]

    var body: some View {
        VStack {

            /// Error! Generic struct 'ForEachDividerView' requires that 'Person' conform to 'Hashable'
            ForEachDividerView(data: people) { person in
                Text(person.name)
            }
        }
    }
}

That's why SwiftUI's ForEach comes with an additional initializer, init(_:id:content:), that takes in a custom key path for extracting the ID. I'd like to take advantage of this initializer in my ForEachDividerView, but I can't figure it out. Here's what I tried:

struct ForEachDividerView<Data, Content, ID>: View where Data: RandomAccessCollection, ID: Hashable, Content: View {
    var data: Data
    var id: KeyPath<Data.Element, ID>
    var content: (Data.Element) -> Content

    var body: some View {
        let enumerated = Array(zip(data.indices, data))

        /// Error! Invalid component of Swift key path
        ForEach(enumerated, id: \.1.appending(path: id)) { index, data in

            content(data)

            if let index = index as? Int, index != enumerated.count - 1 {
                Divider()
                    .background(.blue)
            }
        }
    }
}


/// at least this part works...
ForEachDividerView(data: people, id: \.name) { person in
    Text(person.name)
}

I tried using appending(path:) to combine the first key path (which extracts the element from enumerated) with the second key path (which gets the Hashable property from the element), but I got Invalid component of Swift key path.

How can I automatically add a divider in between the elements of a ForEach, even when the element doesn't conform to Hashable?

CodePudding user response：

Simple way

struct ContentView: View {
let animals = ["Apple", "Bear", "Cat", "Dog", "Elephant"]

var body: some View {
    VStack {

        ForEach(animals, id: \.self) { animal in
            Text(animal)

            if animals.last != animal  {
                Divider()
                    .background(.blue)
            }
        }
    }
}
}

Typically the type inside animals must be Identifiable. In which case the code will be modified as.

          if animals.last.id != animal.id {...}

This will avoid any equatable requirements/ implementations

CodePudding user response：

Found a solution!

appending(path:) seems to only work on key paths erased to AnyKeyPath.
Then, appending(path:) returns an optional AnyKeyPath? — this needs to get cast down to KeyPath<(Data.Index, Data.Element), ID> to satisfy the id parameter.

struct ForEachDividerView<Data, Content, ID>: View where Data: RandomAccessCollection, ID: Hashable, Content: View {
    var data: Data
    var id: KeyPath<Data.Element, ID>
    var content: (Data.Element) -> Content

    var body: some View {
        let enumerated = Array(zip(data.indices, data))

        /// first create a `AnyKeyPath` that extracts the element from `enumerated`
        let elementKeyPath: AnyKeyPath = \(Data.Index, Data.Element).1

        /// then, append the `id` key path to `elementKeyPath` to extract the `Hashable` property
        if let fullKeyPath = elementKeyPath.appending(path: id) as? KeyPath<(Data.Index, Data.Element), ID> {
            ForEach(enumerated, id: fullKeyPath) { index, data in

                content(data)

                if let index = index as? Int, index != enumerated.count - 1 {
                    Divider()
                        .background(.blue)
                }
            }
        }
    }
}

Usage:

struct Person {
    var name: String
}

struct ContentView: View {
    let people: [Person] = [
        .init(name: "Anna"),
        .init(name: "Bob"),
        .init(name: "Chris")
    ]

    var body: some View {
        VStack {
            ForEachDividerView(data: people, id: \.name) { person in
                Text(person.name)
            }
        }
    }
}

Result:

CodePudding user response：

Does everything needs to be in a ForEach? If not, you can consider not using indices at all:

struct ForEachDividerView<Data, Content, ID>: View where Data: RandomAccessCollection, ID: Hashable, Content: View {
    var data: Data
    var id: KeyPath<Data.Element, ID>
    var content: (Data.Element) -> Content
    
    var body: some View {
        if let first = data.first {
            content(first)
            
            ForEach(data.dropFirst(), id: id) { element in
                Divider()
                    .background(.blue)
                content(element)
            }
        }
    }
}