触发退出segue之前如何执行动作？

Question

I have created a segue (present modally) from view controller A to view controller B that is triggered through a button in the navigation controller of view controller A. The modal that takes over is used to send a friend request by typing in an email. When a user types in the email and presses a button to submit the friend request, I want to perform an action triggered by the button (calling a server to send the friend request and returning success if the email exists or returning error if the email doesn't exist). If success, I want to exit/unwind the segue back to A. If error, I don't want to exit/unwind the segue.

I have looked into this question, but it doesn't seem to have the implementation of what I need. I am trying the following:

class BViewController: UIViewController {
    // The button function
    @IBAction func sendFriendRequest(sender: AnyObject) {
        println("Button Function.")
        self.performSegueWithIdentifier("SendFriendRequest", sender: self)
    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "SendFriendRequest" {
            println("Preparing for segue.")
        }
    }

    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.
    }

}

And then in first view controller:

AViewController: UIViewController {
    // The unwind function
    @IBAction func saveFriendRequest(segue:UIStoryboardSegue) {
        println("Finished the segue.")
    }

    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.
    }
}

This is the result when I set up the exit segue for the button (ctrl-drag the button to 'Exit' in the ViewController), I get the calls in this order:

Preparing for segue.
Finished the segue.
Button Function.

However, I don't necessarily want to call the prepareForSegue or the unwind function every time, only if the server gives a success message. So how would I connect things in the storyboard so that when I call performSegueWithIdentifier, I don't have to have call the other functions (prepareForSegue, etc.)?

Answer 1

If you want to the action to perform before the segue, create and if-statement that determines that the action was completed successfully, then perform segue. ie.

if (ActionSuccess) {
self.performSegueWithIdentifier("Segue", sender: nil)
}

Answer 2

Remove the exit segue from the button and instead simply link the button to a new IBAction and insert

self.dismissViewControllerAnimated(true, completion: nil)

So, your new code would be:

@IBAction func saveFriendRequest(sender: AnyObject) {
   //Do your stuff to save the friend request
   self.dismissViewControllerAnimated(true, completion: nil)
}