If you are versed in the ways of Windows Forms and plan on using WPF, brace yourself. The platform might seem somewhat similar at first glance. After that brief initial survey, the landscape changes dramatically. In my opinion, the primary differentiator is the fact that WPF makes heavy of use of something that does not even enter the mental landscape of WinForms. I am talking about templates.
As I explained in the fourth entry of my guided tour of WPF, templates are like a cookie-cutter. Instead of resulting in delicious baked goods, these cookie-cutters produce a tree of visual elements that can render something. What can they render? Anything.
Coming from a background in ASP.NET this concept might seem entirely natural, since the ASP.NET platform has used templates for years. The Repeater control, for example, makes heavy use of templates. The WPF ItemsControl is the moral equivalent of Repeater, in that it produces a static list of items based on a description of visual elements declared in markup.
In WPF there are several types of templates that you use often. They all derive from the abstract FrameworkTemplate class. DataTemplate is used to create a visualization of a non-visual object, such as a business object. ControlTemplate supplies a visual representation of a UI control, such as a Button or ListView. ItemsControl, and all of its subclasses (such as ListBox), create the layout panel that hosts their child elements via an ItemsPanelTemplate. Another commonly used template in WPF is the HierarchicalDataTemplate, which is a data template that has knowledge of how to display a data object’s child objects, such as in a master-detail situation.
The mental shift that I had to make, when leaving WinForms and entering WPF, is that a UI is made of templates. Forget about building a UI and then shoving data into it. That’s not the WPF way. In WPF we show data in a user interface, instead of showing a user interface that contains data. It is a subtle, yet crucial, distinction. If you find yourself creating a UI in WPF and then filling it with data, you are not doing things the WPF way. If you find yourself seeing the UI as a mere “outfit” that data “wears” then you are on the right track. At least, that’s my opinion.