XAML in a Nutshell - Control Elements
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Control elements handle user interaction. Controls are interactive and allow the user to enter data, make choices, and perform other interactive tasks. They can be broken up into five categories: simple controls, content controls, item controls, header item controls, and header content controls. They are differentiated by the attributes they support, namely Content, Headers , and Items . Attribute support is determined by the underlying CLR class represented by the XAML element. Even if you don’t use the Header attribute supported by a header item control, it doesn’t become an item control because the CLR class it represents still has a Header whether or not you assign it a value. Table 3-1 summarizes this information neatly.
Simple controls
Derive directly from the System.Windows.Control class and do not have Content , Items , or Header attributes. Examples of simple controls are HorizontalScrollBar , VerticalScrollBar , Frame , TextBox , and RichTextBox .
Content controls
Have a Content attribute, but no Items or Header attributes. Content controls are restricted to only one element as its content, though that content may be an element (such as a Panel ) that can contain more than one element. Examples of content controls are Button , RepeatButton , Label , RadioButton , CheckBox , ListBoxItem , GroupItem , StatusBarItem , ToolTip , ScrollViewer , and Window .
Item controls
Have an Items attribute, but no Header or Content attributes. Item controls expose a list of elements, usually offering you a choice. Item controls include ListBox , ComboBox , Menu , ContextMenu , RadioButtonList , and TabControl .
Header item controls
Have an Items attribute and a Header attribute but no Content attribute. The Header attribute determines the label for the Items , and the Items attribute contains child elements. The Items attribute is implicitly declared as a sequence of child elements that are not assigned to it. The following declaration of a MenuItem shows how this works:
<MenuItem Header="First Menu Item">
<MenuItem Header="First Child Item" />
<MenuItem Header="Second Child Item" />
</MenuItem>
Header item controls include MenuItem and ToolBar .
Header content controls
Have a Header attribute and a Content attribute, but no Items attribute. Like a content control, the header content control may contain only one child element in its Content attribute. Header content controls include Expander and TabItem .
Table 3-1. Attributes supported by control type
| Content | Header | Items |
|---|
| Simple | N | N | N |
|---|
| Content | Y | N | N |
|---|
| Item | N | N | Y |
|---|
| Header item | N | Y | Y |
|---|
| Header content | Y | Y | N |
|---|
Please check back next week for the continuation of this article.
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 This article is excerpted from chapter 3 of The Basics of XAML, written by Lori A. MacVittie (O'Reilly, 2006; ISBN: 0596526733). Check it out today at your favorite bookstore. Buy this book now.
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