SwiftUI List Children - Cast Empty Array to Optional Array - swiftui

Question

We're using Hierarchical lists in SwiftUI. The List takes an optional array for the children argument children: \.children. We would like to however use a 'non-optional' array
Example from https://developer.apple.com/documentation/swiftui/list
struct ContentView: View {
struct FileItem: Hashable, Identifiable, CustomStringConvertible {
var id: Self { self }
var name: String
var children: [FileItem]? = nil
var description: String {
switch children {
case nil:
return "📄 \(name)"
case .some(let children):
return children.isEmpty ? "📂 \(name)" : "📁 \(name)"
}
}
}
let fileHierarchyData: [FileItem] = [
FileItem(name: "users", children:
[FileItem(name: "user1234", children:
[FileItem(name: "Photos", children:
[FileItem(name: "photo001.jpg"),
FileItem(name: "photo002.jpg")]),
FileItem(name: "Movies", children:
[FileItem(name: "movie001.mp4")]),
FileItem(name: "Documents", children: [])
]),
FileItem(name: "newuser", children:
[FileItem(name: "Documents", children: [])
])
]),
FileItem(name: "private", children: nil)
]
var body: some View {
List(fileHierarchyData, children: \.children) { item in
Text(item.description)
}
}
}
so instead of using
var children: [FileItem]? = nil
we'd like to use
var children: [FileItem] = []
This of course produces a compiler error
Key path value type '[FileItem]' cannot be converted to contextual type '[FileItem]?'
How can one cast from [FileItem] to [FileItem]?

Answer 1

A possible approach is force-unwrapped optional (to fulfil List contract) and initial value and guard setter, so in all places it can be used directly w/o ?. It is the same approach as is used for IBOutlet declarations.
Tested with Xcode 13.4 / iOS 15.5
struct ContentView: View {
struct FileItem: Hashable, Identifiable, CustomStringConvertible {
var id: Self { self }
var name: String
var children: [FileItem]! = [] { // with default !!
didSet {
if children == nil { // guard !!
children = []
}
}
}
var description: String {
children.isEmpty ? "📂 \(name)" : "📁 \(name)" // << direct use !!
}
}
let fileHierarchyData: [FileItem] = [
FileItem(name: "users", children:
[FileItem(name: "user1234", children:
[FileItem(name: "Photos", children:
[FileItem(name: "photo001.jpg"),
FileItem(name: "photo002.jpg")]),
FileItem(name: "Movies", children:
[FileItem(name: "movie001.mp4")]),
FileItem(name: "Documents")
]),
FileItem(name: "newuser", children:
[FileItem(name: "Documents")
])
]),
FileItem(name: "private")
]
var body: some View {
List(fileHierarchyData, children: \.children) { item in
Text(item.description)
}
}
}

Answer 2

What I got from your question is you want to use non-optional array you can update like this.
var children: [FileItem]! = [] {
didSet {
if children.isEmpty {
children = []
}
}
}