FB8367784.swift

// The `Binding.init?(_:)` is unsafe to use and can crash when state goes from non-`nil` to `nil`.
//
// To reproduce:
//
//   * Paste this code over a fresh SwiftUI project's "ContentView.swift"
//   * Run the preview or application
//   * Tap "Bool?" to show the toggle
//   * Tap "Bool?" again to try to hide it and the application will crash.

import SwiftUI

struct ContentView: View {
  @State var bool: Bool?

  var body: some View {
    VStack {
      Button("Bool?") {
        self.bool = self.bool == nil ? false : nil
      }
      if let $bool = Binding(self.$bool) {
        Toggle("Bool", isOn: $bool)
      }
    }
  }
}

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

@stephencelis could be related to animations. Adding .transition(.identity) to Toggle prevents the crash for me.

@iampatbrown Good sleuthing :) My guess is Apple just hasn't used this API much, which is a shame, because it's really useful!

Thank you! Added a duplicate FB. I notice the custom solution in the episode suffers from a glitchy animation. At least it works, though. :)

@rayfix The episode code is simplified, but I believe swiftui-navigation handles animation correctly. It does so by writing through the binding's transaction:

https://github.com/pointfreeco/swiftui-navigation/blob/7a61fb419997f56bd9928c7b405fc7557a60d4bd/Sources/SwiftUINavigation/Binding.swift#L41

(Thanks to @iampatbrown for that particular solution to the problem!)