Conditional Segue while passing data?

Question

I'm trying to make the segue from viewcontroller to 2ndviewcontroller only when my condition is met. I've connected the segue from the button in viewcontroller to the 2ndviewcontroller. So far I have:

@IBAction func switchView(_ sender: AnyObject) {
        // if a and b's textfields aren't empty
        if(!(a.text?.isEmpty)! && !(b.text?.isEmpty)!) {
            a1 = a.text!;
            b1 = b.text!;
        }else{
            // do something
        }

    }

override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {
    if(identifier == "2ndviewcontroller") {
        if(!(a.text?.isEmpty)! && !(b.text?.isEmpty)!)  {
            return true
        }
    }
    return false
}

With this, I've been able to make the segue ONLY when a and b's textfields are not empty. That's exactly what I want but I also want to pass data from viewcontroller to 2ndviewcontroller as well.

func prepForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "2ndviewcontroller" {
         let 2ndviewcontroller = segue.destination as! 2ndviewcontroller
            2ndviewcontroller.c = a

        }
    }
}

I used the code above to pass data from viewcontroller to 2ndviewcontroller. Problem is I don't know how to combine them to both pass data, AND only make the segue when condition is met. When I have both functions, the bool function executes correctly, but prepForSegue does not pass data. When I comment out the bool function, prepForSegue passes the data, but I'm cannot apply a condition for making the segue.

Edit: fixed by using prepareForSegue method provided in the comments below.

Answer 1

As discussed in the comments, the method name should be prepareForSegue, not prepForSegue.