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Getting the code perfect is not the point of this exercise. It s OK if your application doesn t look exactly like my screenshot. The main objective was to get you familiar with setting and resetting inline properties in Expression Blend. In these two exercises, you saw how to change the appearance of your Silverlight applications using inline properties in Visual Studio 2008 and Expression Blend. Although this method is very straightforward, in a normal application with a lot of controls, setting all of the properties can become tedious. And if you need to change the appearance of some elements throughout the application, it will not be an easy task. This is where Silverlight styles come in.

In the previous section, you saw how you can change the appearance of a Silverlight application by setting inline properties. This works perfectly fine, but it presents maintenance problems. From a maintenance perspective, it s better to separate the style properties from the control definitions. For example, consider the following TextBlock definition:

<TextBlock Grid.Row="0" Grid.Column="0" Text="First Name"

Suppose you defined all your TextBlock controls this way, throughout your application. Then, if you wanted to update the look of your application s text boxes, you would need to modify the TextBox definitions one by one. To save time and avoid errors, it s preferable to be able to make updates to properties related to the control s appearance in one central location, rather than in each instance of the control. This problem is certainly not new to Silverlight. Developers and designers have faced this challenge for years with HTML-based pages. HTML solves the problem with a technology known as Cascading Style Sheets (CSS). Instead of specifying the different attributes of HTML controls directly, developers can simply specify a style for the control that corresponds to a style in a style sheet. The style sheet, not the HTML, defines all of the different appearance attributes for all controls. This way, if developers want to adjust an attribute of a control in an application, they can change it in the style sheet one time, and that change will be automatically reflected in every control in the application that references that style. Silverlight offers a similar solution. Silverlight allows you to create style resources, in much the same way you would define styles in a CSS style sheet. In Silverlight, style resources are hierarchical, and can be defined at either the page level or the application level. If defined at the page level, the styles will be available only to controls on that page. Styles defined at the application level can be utilized by controls on all pages across the entire application. The Silverlight Style Hierarchy section later in this chapter provides more information about the style hierarchy. A Silverlight style is defined using the <Style> element, which requires two attributes: the Key attribute represents the name of the style, and the TargetType attribute tells Silverlight which type of control gets the style. Within the <Style> element, the style is made up of one or more <Setter> elements, which define a Property attribute and a Value attribute. As an example, the preceding TextBlock control s appearance properties could be defined in the following Silverlight style definition:

<Style x:Key="FormLabel" TargetType="TextBlock"> <Setter Property="FontFamily" Value="Verdana"/> <Setter Property="FontSize" Value="16"/> <Setter Property="FontWeight" Value="Bold"/> <Setter Property="Margin" Value="5,5,5,5"/> </Style>

In HTML, to reference a style from a control, you simply set the style attribute. In Silverlight, this syntax looks a little different. Silverlight styles are referenced in a control using an XAML markup extension. You saw markup extensions in use in 5 when