Cocoa Programming for OS X: The Big Nerd Ranch Guide

Challenge: Encapsulate Sheet Presentation

In Dice, add a method to ConfigurationWindowController: presentAsSheetOnWindow(_:completionHandler:). The method’s parameter should be the window the configuration sheet should be displayed on, and the completion handler will be a closure of type (DieConfiguration?)->(Void). If the user clicks OK, the DieConfiguration will be passed to the completion handler; otherwise it will be nil to signal that nothing changed.

Here is how your method will look when it is called:

      windowController.presentAsSheetOnWindow(window, completionHandler: {
        configuration in
          if let configuration = configuration {
              dieView.color = configuration.color
              dieView.numberOfTimesToRoll = configuration.rolls
          }
      })