If you create a new WinRT solution using the Grid or Split Application Template you'll get all the code you need to create a layout aware page that shows a different view when in snap view. If you start of your project using the blank project template, you need to do a little bit more work to get it working.

First you need to change the page to be a layout aware page. LayoutAwarePage is a class provided by the template and is in the Common folder.

In BlankPage.xaml.cs change:

public sealed partial class BlankPage : Page

to

public sealed partial class BlankPage : LayoutAwarePage

In … more