One of the primary objectives of WPF was to bring together the best features of both Windows development and the Web model. Before we look at the features of WPF, it is important to understand the new programming model in the .NET Framework 3.0: XAML.
A Brief Look at the XAML Programming Model
One of the major, and often misunderstood, features of .NET 3.0 is the new XAML programming model. XAML provides a set of semantics on top of raw XML that enables a common interpretation. To oversimplify slightly,XAML is an XML-based instantiation script for CLR objects. There is a mapping from XML tags to CLR types, and from XML attributes to CLR properties and events. The following example shows an object being created and a property being set in both XAML and C#:
// C# version
MyObject obj = new MyObject();
obj.SomeProperty = 1;
XAML was created to be a markup language that integrated well with the CLR and provided for rich tool support. A secondary goal was to create a markup format that was easy to read and write. It may seem a little rude to design a feature of the platform that is optimized first for tools, then for humans, but the WPF team felt strongly that WPF applications would typically be authored with the assistance of a visual design tool like Microsoft Visual Studio or Microsoft Expression. To walk the line between tools and humans, WPF allows the type author to define one property to be the content property.
For further readability, XAML has a feature known as markup extensions. This is a general way to extend the markup parser to produce simpler markup. Markup extensions are implemented as CLR types, and they work almost exactly like CLR attribute definitions. Markup extensions are enclosed in curly braces, { }. For example, to set a property value to the special value null, we can use the built-in Null markup extension:
In the next post we will see the layouts in WPF and their usage in detail.
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