@tvhong: Thank you for writing. I think I say -- several times -- that our goal here is to create Windows 10 apps. I even demonstrated their use in the stock apps that are distributed on Windows 10 (Money, Sports, Travel, etc. along with Settings and others). If you've NOT used Windows 10, then you may need to spend time using it to really understand why the SplitView is important. Looking through the transcripts of this lesson and the lessons leading up to this, I can see that I did talk about this and where we're headed --> creating hamburger style navigation.
Outside of the "hamburger style navigation" I personally can't see any other practical use of this control. When should you use this? When you're working with a data intensive application and you intend to distribute your app via the Windows Store.
@tvhong: Remember the parenthesis ( ) are used as a method invocation operator. When creating a new instance of a class, you use ( ) to indicate you want to call the constructor of that class (at least, that's how I always understood their purpose).
@Dan: I'm willing to bet that either (1) your folder is named Model, not Models, or (2) the Book class is not in the Models namespace. I would take a close look at the Book class definition, the EXACT name of the folder, namespace, class. If it's not that, then I would probably need to see your code.
@tvhong: In my mind any class that has a visual aspect to it is a control. I would say that you could use XAML to utilize all controls, but not every XAML element is a control. For example, in the App.xaml, or even the Page.xaml at the highest level a Page is not a control. Furthermore, there are things that we'll discuss later regarding animation and such that are expressed in XAML, but are not controls.
XAML is just a concise way to create instances of classes. It's not exclusive to user interfaces (for example, Windows Workflow Foundation) utilizes XAML.
@TomaszS: Yes, #70 allows the user to pay to unlock a feature. However, a trial version is implemented a bit differently but very close to the same basic procedure. The URL in the video will take you to Windows Dev Center and the instructions will be in that same area of help. Good luck!!!