Binding to XML
From John Papa, MSDN magazine
Binding to data sources such as XML and objects is also handy. Figure 4 shows a sample of an XmlDataProvider that contains an embedded list of colors that will be used as a data source. The XmlDataProvider can be used to bind to an XML document or fragment that is either embedded in the XmlDataProvider tag or is in a file referred to in an external location.
<StackPanel>
<StackPanel.Resources>
<XmlDataProvider x:Key="MoreColors" XPath="/colors">
<x:XData>
<colors >
<color name="pink"/>
<color name="white"/>
<color name="black"/>
<color name="cyan"/>
<color name="gray"/>
<color name="magenta"/>
</colors>
</x:XData>
</XmlDataProvider>
Embedded XML content must be placed within a tag inside of an XmlDataProvider, as shown in Figure 4. The XmlDataProvider must be given an x:Key value so that it can be referred to by data-binding targets. Notice that the XPath attribute is set to “/colors”. This attribute defines the level of the XML content that will be used as the data source. This becomes very useful when binding to a large XML structure that may be contained in a file or database and the data you want to bind to is not the root element.
An XmlDataProvider is a resource that can be placed inside of a context-specific resource. As Figure 4 shows, the XmlDataProvider is defined as a resource within the context of the StackPanel. This means that the XmlDataProvider will be available to all content inside of that StackPanel. Setting the context of a resource helps limit the exposure of a data source to the appropriate areas. This enables you to create well-defined, self-contained regions of both controls and supporting resources within your page, thus improving readability.
The syntax for binding to a resource is slightly different than it is for binding to an element. When binding to a control, you set the ElementName and the Path properties of the Binding. However, when you bind to a resource you set the Source and, since we are binding to an XmlDataProvider, you set the XPath property of the Binding as well. For example, the following code will bind the ListBox’s items to the MoreColors resource. The Source property is set to a resource and it is specified as a StaticResource named MoreColors. The XPath property indicates that the items will be bound to the
element’s name attribute within the XML data source:
<ListBox x:Name="lbColor" Width="248" Height="56"
IsSynchronizedWithCurrentItem="True"
ItemsSource="{Binding Source={StaticResource MoreColors},
XPath=color/@name}">
</ListBox>
I specified StaticResource in this case because the XML will not change. If changes occur in the data source, they will not be sent to the target. The DynamicResource setting indicates the opposite—changes will be sent. This is useful when referencing system themes, languages in globalization, or fonts. A DynamicResource will allow these types of settings to be propagated throughout the UI elements that are bound to them dynamically.
The XmlDataProvider can also point to an external source for the XML content. For my example, I have a file named colors.xml that contains the list of colors I want my ListBox to be bound to. I can simply add a second XmlDataProvider resource to the StackPanel and direct it to the XML file. Notice I set the Source attribute to the name of the XML file and the x:Key to Colors:
<XmlDataProvider x:Key="Colors" Source="Colors.xml" XPath="/colors"/>
Both XmlDataProviders exist as resources within the same StackPanel. I can tell the ListBox to bind itself to this new resource by changing the name that the StaticResource is set to:
<ListBox x:Name="lbColor" Width="248" Height="56"
IsSynchronizedWithCurrentItem="True"
ItemsSource="{Binding Source={StaticResource Colors},
XPath=color/@name}">
</ListBox>
