Programming WPF, 2nd Edition

Properties

In Example A-1, we set the Window element's Title property. This property's type was String. Pure text properties are a natural fit with XML, because XML is a text-based format. But what about other property types? Example A-13 uses a slightly wider range of types.

Example A-13. Nonstring properties

<Rectangle Width="100"
              Height="20"
              Stroke="Black"
              Fill="#80FF40EE" />

None of the properties set here is a string. Both Width and Height are of type Double, whereas both Stroke and Fill require a Brush. In order to support diverse property types, XAML relies on .NET's TypeConverter system. This has been around since v1.0 of .NET, and it is used in design-time scenarios. A TypeConverter maps between different representations of a value, most commonly between String and a property's native type.^[120]

The Width and Height properties are converted using the LengthConverter type. (WPF knows to use this type because the FrameworkElement class's Width and Height properties are marked with a TypeConverterAttribute indicating which converter to use.) The BrushConverter class is used for the other two properties, because although they do not have a TypeConverterAttribute, they are of type Brush, and the Brush type has a TypeConverterAttribute indicating that BrushConverter should be used. Example A-14 illustrates how the attribute was applied in each case.

Example A-14. Specifying a TypeConverter

public class FrameworkElement : UIElement, ... {
    ...
    [TypeConverter(typeof(LengthConverter)) ...