将数据传递到导航控制器中的另一个视图控制器

Question

I have two view controllers (fitstViewController.swift and secondViewController.swift) in navigation controler.

My idea is that In firstViewController there are a button and a textFIeld. When I click the button, value in the textField is passed to secondViewController.

However it makes an error "Thread 1: signal SIGABRT" in the first controller.

Here is the code in the first controller..

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    let destination = segue.destinationViewController as! UINavigationController

    let detailController = destination.topViewController as! secondViewController

    detailController.stockSymbol = textField.text
}

I added just one line in the second controller..

    var stockSymbol:String!

How can it be solved?

Thank you in advance!

Answer 1

In second controller the declared variable should be

 var stockSymbol:String?

You should not force unwrap it unless you are sure that it would never be nil.

Answer 2

Replace your old code by:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    guard let destination = segue.destinationViewController as? SecondViewController else { return } 
    destination.stockSymbol = textField.text
}