如何添加一个覆盖故事板序列的按钮（快速3）

Question

I added a storyboard segue to add text to a photo. Right now you would have to go through 3 view controllers to get the final photo. A(options menu) -> B(enter text) -> C(take photo). If I add a button to vc b it shows up as a sigabrt error. If I comment out the code below there is no error. Its obvious the issue is the storyboard segue. All i want to do is have a button that can go from b->a without a runtime error coming up. The code below is vc b. Just to let you know I can go from c ->a no problem but I want to go from b -> a

import UIKit

class customViewController: UIViewController {

@IBOutlet weak var zext: UITextField!
override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view.
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
   var destviewc: ccViewController = segue.destination as! ccViewController
    destviewc.labelText = zext.text!


} }

Answer 1

Your implementation of prepare(for:sender:) is making runtime assumptions about the presence of certain values (using ! ). Namely, that segue.destination is a ccViewController and zext.text is not nil. If these assumptions are incorrect you will experience a runtime error.

Instead you can employ some defensive techniques using the Swift guard statements to ensure your method is in the right state to continue execution.

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    guard let destViewC = segue.destination as? CCViewController else {
        return
    }

    guard let text = zext.text else {
        return
    }

    destViewC.labelText = text
}

Also, type names should use upper camel case. That is, "customViewController" should be "CustomViewController".