Implementing an unwind method for the Cancel button

Eventually, you will calculate an overall rating by averaging the ratings that have been submitted by users via the Review Form screen, but at the moment, when you tap the Add Review button, the Review Form screen doesn't have a ratings view. Also, you can't dismiss the Review Form screen by tapping on the Cancel button. Let's fix that first. Just as you did with the Locations screen, you need to implement an unwind method to dismiss the Review Form screen. Take the following steps:

1. Click RestaurantDetailViewController.swift in the Project navigator.
2. Add the following code to the private extension, before the createRating() method:

@IBAction func unwindReviewCancel(segue:UIStoryboardSegue) {}

This method will dismiss the Review Form screen.

3. Open ReviewForm.storyboard and Ctrl + Drag from the Cancel button to...