In my viewDidAppear, how do I know when it's being unwound by a child?

Question

When my child performs an unwind segue, my controller\'s viewDidAppear gets called.

In this method (and this method alone, I need to know whether it was from an unwi

Answer 1

Your question was really interesting to me, because I never used IB and segues before (don't judge me for that) and wanted to learn something new. As you described in your comments:

viewDidAppear will be called on B when C rewinds to A

So I come up with an easy custom solution to this:

protocol ViewControllerSingletonDelegate: class {

    func viewControllerWillUnwind(viewcontroller: UIViewController, toViewController: UIViewController)
}

class ViewControllerSingleton {

    static let sharedInstance = ViewControllerSingleton()

    private var delegates: [ViewControllerSingletonDelegate] = []

    func addDelegate(delegate: ViewControllerSingletonDelegate) {

        if !self.containsDelegate(delegate) {

            self.delegates.append(delegate)
        }
    }

    func removeDelegate(delegate: ViewControllerSingletonDelegate) {

        /* implement any other function by your self :) */
    }

    func containsDelegate(delegate: ViewControllerSingletonDelegate) -> Bool {

        for aDelegate in self.delegates {

            if aDelegate === delegate { return true }
        }

        return false
    }

    func forwardToDelegate(closure: (delegate: ViewControllerSingletonDelegate) -> Void) {

        for aDelegate in self.delegates { closure(delegate: aDelegate) }
    }
}


class SomeViewController: UIViewController, ViewControllerSingletonDelegate {

    let viewControllerSingleton = ViewControllerSingleton.sharedInstance

    func someFunction() { // some function where you'll set the delegate

        self.viewControllerSingleton.addDelegate(self)
    }

    /* I assume you have something like this in your code */
    @IBAction func unwindToSomeOtherController(unwindSegue: UIStoryboardSegue) {

        self.viewControllerSingleton.forwardToDelegate { (delegate) -> Void in

            delegate.viewControllerWillUnwind(unwindSegue.sourceViewController, toViewController: unwindSegue.destinationViewController)
        }

        /* do something here */
    }

    // MARK: - ViewControllerSingletonDelegate
    func viewControllerWillUnwind(viewcontroller: UIViewController, toViewController: UIViewController) {

        /* do something with the callback */
        /* set some flag for example inside your view controller so your viewDidAppear will know what to do */
    }
}

You also could modify the callback function to return something else, like controller identifier instead the controller itself.

I do everything programmatically, so please don't judge me for that too. ;)

If this code snippet won't help you, I'd still love to see some feedback.