Swift：在展开可选值NSObject时意外发现nil

Question

Using Swift 2 and Xcode 7 in an IOS app, I'm trying to avoid the fatal error unexpectedly found nil while unwrapping an Optional value applying the optional chaining to a FriendShip NSObject but I don't know which is the correct way.

The class FriendShip showed below receives a nil value in the friend property but the compiler gives me the fatal error unexpectedly found nil while unwrapping an Optional value :

class FriendShip: NSObject{

  var id: String?
  var friend: User?
  var date: NSDate?

  init(dictionary: [String: AnyObject]){

    id        = dictionary["id"] as? String
    friend    = User(dictionary: (dictionary["friend"] as! [String: AnyObject]))
    date      = dictionary["date"] as? NSDate

  }
} 

but if I set the friend property to optional, the compiler gives me an EXC_BAD_INSTRUCTION error:

class FriendShip: NSObject{

  var id: String?
  var friend: User?
  var date: NSDate?

  init(dictionary: [String: AnyObject]){

    id        = dictionary["id"] as? String
    friend    = User(dictionary: (dictionary["friend"] as? [String: AnyObject])!)
    date      = dictionary["date"] as? NSDate

  }
}  

How could I solve it?

Answer 1

You're still unwrapping an optional here:

friend    = User(dictionary: (dictionary["friend"] as? [String: AnyObject])!)

Namely:

(dictionary["friend"] as? [String: AnyObject])!

This should be instead something like:

if let friendDictionary = dictionary["friend"] as? [String: AnyObject] {
    friend = User(dictionary:friendDictionary)
}