Changes

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</pre>

The application now has a content view controller and a data model from which the content of each page will be extracted by the data source methods. The next logical step, therefore, is to implement those data source methods. As previously outlined in [[Implementing a Page based iOS 9 Application with UIPageViewController]], instances of the UIPageViewController class need a data source. This takes the form of two methods, one of which is required to return the view controller to be displayed after the currently displayed view controller, and the other the view controller to be displayed before the current view controller. Since the ViewController class is going to act as the data source for the page view controller object, these two methods, together with two convenience methods (which we will borrow from the Xcode Page-based Application template) will need to be added to the ViewController.swift file. Begin by adding the two convenience functions: