Quick tip: Avoid crash when using ForEach & Bindings in SwiftUI

If you’ve played around with ForEach and .onDelete in SwiftUI you might have encountered a crash due to ‘Index out of range‘ when you delete elements that are referenced with a binding (eg. a Toggle within your ForEach closure)

This occurs due to a race condition of sorts… SwiftUI is trying to read from the old binding after the index it references has already been deleted. In other words: it is trying to update the view that is about to be removed before the ForEach has been refreshed.

This is a bug in SwiftUI, and will hopefully be fixed with upcoming releases.

But for now… here is an extension on Binding that provides a ‘safe’ subscript that avoids this crash. Note that this only prevents a crash on subsequent access , you still need to provide a valid index when creating it (so that our binding remains non-optional).

extension Binding where Value: MutableCollection
{
  subscript(safe index: Value.Index) -> Binding<Value.Element>
  {
    // Get the value of the element when we first create the binding
    // Thus we have a 'placeholder-value' if `get` is called when the index no longer exists
    let safety = wrappedValue[index]
    return Binding<Value.Element>(
      get: {
        guard self.wrappedValue.indices.contains(index)
          else { return safety } //If this index no longer exists, return a dummy value
        return self.wrappedValue[index]
    },
      set: { newValue in
        guard self.wrappedValue.indices.contains(index)
          else { return } //If this index no longer exists, do nothing
        self.wrappedValue[index] = newValue
    })
  }
}