MyDisclosureGroup.swift

// Final implementation of MyDisclosureGroup
// read more at https://www.fivestars.blog

import SwiftUI

struct MyDisclosureGroup<Label, Content>: View where Label: View, Content: View {
  @State private var myIsExpanded: Bool = false
  private var isExpanded: Binding<Bool>?
  var content: () -> Content
  var label: () -> Label

  public init(isExpanded: Binding<Bool>, content: @escaping () -> Content, label: @escaping () -> Label) {
    self.init(isExpanded: .some(isExpanded), content: content, label: label)
  }

  public init(content: @escaping () -> Content, label: @escaping () -> Label) {
    self.init(isExpanded: nil, content: content, label: label)
  }

  private init(isExpanded: Binding<Bool>?, content: @escaping () -> Content, label: @escaping () -> Label) {
    self.isExpanded = isExpanded
    self.content = content
    self.label = label
  }

  private struct OriginalDisclosureGroup<Label, Content>: View where Label: View, Content: View {
    @Binding var isExpanded: Bool
    var content: () -> Content
    var label: () -> Label

    @ViewBuilder
    var body: some View {
      Button(action: { isExpanded.toggle() }, label: label)
      if isExpanded {
        content()
      }
    }
  }

  var body: some View {
    OriginalDisclosureGroup(
      isExpanded: isExpanded ?? $myIsExpanded,
      content: content,
      label: label
    )
  }
}

struct ContentView: View {
  @State var showingContent = true

  @ViewBuilder
  var body: some View {

    // no binding
    MyDisclosureGroup {
      Text("Content")
    } label: {
      Text("Tap to show content")
    }
    .padding(.all, 20)

    // binding
    MyDisclosureGroup(isExpanded: $showingContent) {
      Text("Content")
    } label: {
      Text("Tap to show content")
    }
    .padding(.all, 20)
  }

}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
          .previewLayout(.sizeThatFits)
    }
}