Dynamic Cast Faild - AnyObject to NSArray - iphone

Question

I am trying to read textFields values which is coming trough alert controller but I am getting run time error on casting with Anyobject to NSArray
alertUserStatus.addAction(UIAlertAction(title: "Sign Up", style: UIAlertActionStyle.Default, handler: {
alertAction in
//let textField:NSArray=alertUserStatus.textFields as AnyObject! as NSArray
let textField=alertUserStatus.textFields! as AnyObject! as NSArray
let username:String=textField.objectAtIndex(0) as String
let password:String=textField.objectAtIndex(1) as String
var signUpUser=PFUser()
signUpUser.username=username
signUpUser.password=password
signUpUser.signUpInBackgroundWithBlock{
(success:Bool!,error:NSError!)->Void in
if success == true {
println("sign up successfully")
}
else{
println("fail to sign up")
}
}
}))

Answer 1

It always helps to look at the type you are getting from a function before trying to massage it into another type. In this case alertUserStatus.textFields returns [AnyObject]? – that is, an optional array of AnyObject. So there’s really no need to convert it to an AnyObject and then to an NSArray just so you can get the first two entries from it. Instead you want to unwrap it and convert it to an array of String.
It’s also best to avoid using !, even if you’re confident the optional can’t possibly be nil, because one of these days there’ll be an edge case that you miss that doesn’t hold and your code will crash with an inexplicable force-unwrap error message.
// nb you can skip the handler: argument name with trailing-closure syntax
alertUserStatus.addAction(UIAlertAction(title: "Sign Up", style: UIAlertActionStyle.Default) {
alertAction in
if let textFields = alertUserStatus.textFields as? [String] where textFields.count > 1 {
let username = textFields[0]
let password = textFields[1]
// rest of your code...
}
else {
// assert with intelligible message or log error or similar
}
})