add Hierarchy-List code snippet

Hierarchy-List/ContentView.swift

@@ -0,0 +1,90 @@
+// Original article here: https://www.fivestars.blog/code/swiftui-hierarchy-list.html
+
+import SwiftUI
+
+struct FileItem: Identifiable {
+  let name: String
+  var children: [FileItem]?
+
+  var id: String { name }
+
+  static let spmData: [FileItem] = [
+    FileItem(name: ".gitignore"),
+    FileItem(name: "Package.swift"),
+    FileItem(name: "README.md"),
+    FileItem(name: "Sources", children: [
+      FileItem(name: "fivestars", children: [
+        FileItem(name: "main.swift")
+      ]),
+    ]),
+    FileItem(name: "Tests", children: [
+      FileItem(name: "fivestarsTests", children: [
+        FileItem(name: "fivestarsTests.swift"),
+        FileItem(name: "XCTestManifests.swift"),
+      ]),
+      FileItem(name: "LinuxMain.swift")
+    ])
+  ]
+}
+
+struct ContentView: View {
+  let data: [FileItem] = .spmData
+
+  var body: some View {
+//    List(data, children: \.children, rowContent: { Text($0.name) })
+    HierarchyList(data: data, children: \.children, rowContent: { Text($0.name) })
+  }
+}
+
+public struct HierarchyList<Data, RowContent>: View where Data: RandomAccessCollection, Data.Element: Identifiable, RowContent: View {
+  private let recursiveView: RecursiveView<Data, RowContent>
+
+  public init(data: Data, children: KeyPath<Data.Element, Data?>, rowContent: @escaping (Data.Element) -> RowContent) {
+    self.recursiveView = RecursiveView(data: data, children: children, rowContent: rowContent)
+  }
+
+  public var body: some View {
+    List {
+      recursiveView
+    }
+  }
+}
+
+private struct RecursiveView<Data, RowContent>: View where Data: RandomAccessCollection, Data.Element: Identifiable, RowContent: View {
+  let data: Data
+  let children: KeyPath<Data.Element, Data?>
+  let rowContent: (Data.Element) -> RowContent
+
+  var body: some View {
+    ForEach(data) { child in
+      if self.containsSub(child)  {
+        FSDisclosureGroup(content: {
+          RecursiveView(data: child[keyPath: self.children]!, children: self.children, rowContent: self.rowContent)
+          .padding(.leading)
+        }, label: {
+          self.rowContent(child)
+        })
+      } else {
+        self.rowContent(child)
+      }
+    }
+  }
+
+  func containsSub(_ element: Data.Element) -> Bool {
+    element[keyPath: children] != nil
+  }
+}
+
+struct FSDisclosureGroup<Label, Content>: View where Label: View, Content: View {
+  @State var isExpanded: Bool = false
+  var content: () -> Content
+  var label: () -> Label
+
+  @ViewBuilder
+  var body: some View {
+    Button(action: { self.isExpanded.toggle() }, label: { label().foregroundColor(.blue) })
+    if isExpanded {
+      content()
+    }
+  }
+}

Hierarchy-List/README.md

@@ -0,0 +1,6 @@
+Code snippet from [SwiftUI Hierarchy Lists][fs].
+
+![][gif]
+
+[fs]: https://fivestars.blog/articles/swiftui-hierarchy-list/
+[gif]: spm.gif