Optional error while converting from Swift 2 to 3 in keyboardWillShow notification - ios

Question

I am converting my app to Swift 3 at the moment and I have problems with this function I used to show the keyboard before.
Initializer for conditional binding must have Optional type, not 'CGFloat'
The error appears in the third line.
It's been a while since I've programmed the last time and so I am not sure how to solve this.
func keyboardWillShow(_ sender: Notification) {
if let userInfo = sender.userInfo {
if let keyboardHeight = (userInfo[UIKeyboardFrameEndUserInfoKey] as AnyObject).cgRectValue.size.height {
let duration = (userInfo[UIKeyboardAnimationDurationUserInfoKey] as AnyObject).doubleValue
let edgeInsets = UIEdgeInsetsMake(0, 0, keyboardHeight, 0)
UIView.animate(withDuration: duration!, animations: { () -> Void in
self.tableView.contentInset = edgeInsets
self.tableView.scrollIndicatorInsets = edgeInsets
self.view.layoutIfNeeded()
})
}
}
}

Answer 1

This is one of those rare situations where I recommend force-unwrapping. You know the userInfo contains this information, and you are hosed if it doesn't. Moreover, there is no need to pass through AnyObject or to call cgRectValue; you can cast all the way down to a CGRect in a single move. So I would write:
let keyboardHeight = (userInfo[UIKeyboardFrameEndUserInfoKey] as! CGRect).size.height
(Note that there is no if, because we are not doing a conditional binding; we simply cast, kaboom.)
[Note too that there is no need now to fetch the duration or to call animate or layoutIfNeeded; you can throw all of that away. We are already in an animation, and your changes to the contentInset and scrollIndicatorInsets will be animated in time to the keyboard.]

Answer 2

change
if let keyboardHeight = (userInfo[UIKeyboardFrameEndUserInfoKey] as AnyObject).cgRectValue.size.height {
to
if let foo = userInfo[UIKeyboardFrameEndUserInfoKey] {
let keyboardHeight = (foo as as AnyObject).cgRectValue.size.height
--- UPDATE ---
or
if let keyboardHeight = (userInfo[UIKeyboardFrameEndUserInfoKey] as AnyObject?).cgRectValue.size.height {
AnyObject? works because AnyObject can contain Optional itself. So you have to casting to Optional explicitly. Either AnyObject? or Optional<AnyObject> will work.