Swift Xcode 6 If Else statement check letters or numbers - swift

Question

I am trying to write and if else statement.
I need it to check if atextField is empty or has letters and if the textfield is empty or has letters is triggers a UIAlertWIndow.
I have tried boolean methods to no avail.
Any ideas?
This is what I have written so far:
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
if self.numOfGuestsData.text == "" {
alert()
println("Something Amish")
let alertController = UIAlertController(title: "Split The Bill", message:
"Please Enter The Number of Guests!", preferredStyle: UIAlertControllerStyle.Alert)
alertController.addAction(UIAlertAction(title: "Okay", style: UIAlertActionStyle.Default,handler: nil))
presentViewController(alertController, animated: true, completion: nil)
} else if self.numOfGuestsData.text != "" {
let subTotalVC = segue.destinationViewController as subTotalAmountViewController
subTotalVC.numOfGuests = numOfGuestsData.text
println("everything is Ok Here")
}
}
Also if I take out the alert window the if else statement fails for some reason.
Like if I write it like this:
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
if self.numOfGuestsData.text == "" {
alert()
println("Something Amish")
} else if self.numOfGuestsData.text != "" {
let subTotalVC = segue.destinationViewController as subTotalAmountViewController
subTotalVC.numOfGuests = numOfGuestsData.text
println("everything is Ok Here")
}
}
It just goes to the else...

Answer 1

Are you trying to suppress the segue if the textField is empty and present a UIAlertController instead if that is the case? Are you using a show segue? I think your logic needs to be moved out of prepareForSegue: and moved into shouldPerformSegueWithIdentifier:. Do your check in that method. Doing the logic in prepareForSegue: is too late; the segue is definitely going to happen by then.
Basically, you'll override shouldPerformSegueWithIdentifier: and then either return true or return false based on your logic. If it returns false, the segue won't happen.
Documentation here.