Why I am getting 'valueForUndefinedKey' error when using AnyObject in Swift?

Question

Im have a question. Why the following crash reason? since "name" exists?

viewcontroller1:

struct pointDict {
    let id: Int
    let name: String
}
var pointsPlane: [pointDict] = []

let wp = pointDict(id: 123, name: "test")
pointsPlane.append(wp)

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {


if let destVC = segue.destination as? viewcontroller2 {
destVC.dt = pointsPlane[0] as AnyObject

}
}

viewcontroller2:

var dt: AnyObject?
let detail = self.dt
name.text = detail?.value(forKeyPath: "name") as? String

Crash Report:

valueForUndefinedKey:]: this class is not key value coding-compliant for the key name

Answer 1

AnyObject is reference type but a struct is value type and therefore is not ObjC key-value coding compliant.

Your approach is bad practice anyway. A swiftier way is to declare the properties with the real type. The default declaration of detail in the template is not needed.

viewcontroller1:

struct PointDict {
    let id: Int
    let name: String
}
var pointsPlane: [PointDict] = []

let wp = PointDict(id: 123, name: "test")
pointsPlane.append(wp)

override func prepare(for segue: UIStoryboardSegue, sender: Any?) 
    if let destVC = segue.destination as? viewcontroller2 {
        destVC.dt = pointsPlane.first
    }
}

viewcontroller2:

var dt : PointDict? 

override func viewDidLoad() {
    super.viewDidLoad()
    name.text = dt?.name ?? ""
}