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The XmlDataSource control exists merely as a proxy for retrieving XML data, which can then be programmatically accessed or bound to a data Web control. To access XML data from an ASP.NET page using the XmlDataSource control, start by dragging the control from the Toolbox onto the Designer (the XmlDataSource control is found in the Data section of the Toolbox). From the XmlDataSource‘s smart tag, click the "Configure Data Source" link to bring up the Configure Data Source wizard (shown below). From the wizard, you can set the XmlDataSource control‘s three most useful properties:
DataFile
- specifies the file that contains the XML data to access. This can be a local
file, like ~/App_Data/XMLFile.xml, or a remote file,
like http://msdn.microsoft.com/rss.xml.TransformFile
- XML documents can be transformed from one structure to another using a
markup language known as XSL
Transformations, or XSLT. If you want to transform the XML contents in
DataFile before working with the XML data, specify the XSLT file
to perform the transformation here. For more information on XSLT, check out
the XSLT Tutorial at W3
Schools.XPath
- XPath is an XML syntax used to filter the contents of an XML document,
returning a particular value or nodeset. If you want to work with a particular
set of XML data, specify an XPath expression here to limit the results. See W3
School‘s XPath
tutorial for more information.
If you do not have the XML data or XSLT saved in a file, you can specify the
raw XML or XSLT directly through the XmlDataSource‘s Data
and Transform
properties. These properties cannot be set through the Configure Data Source
wizard, but instead must be set through the Properties window. (Click on the
XmlDataSource control in the Designer and hit F4.)
Once you‘ve configured the XmlDataSource control, add a data Web control to
the page and set its DataSourceID property to the ID
of the XmlDataSource control (a task that can easily be done through the
drop-down list in the data Web control‘s smart tag). ASP.NET 2.0 offers two new
databinding methods for accessing a particular value or noteset from the XML
data bound to the data Web control:
XPath("xpath") - accesses a
particular value. To retrieve the text value of a node, simply refer to the
node in the xpath; for an attribute, prefix the attribute name with
@.XPathSelect("xpath") - returns a
nodeset. Can be used to bind a set of nodes to a nested data Web control.These databinding statements must appear within a template. For controls like the GridView and DetailsView, which are composed of fields (like BoundFields, CheckBoxFields, and so on), use TemplateFields for each field you want to display.
RSS, or Really Simple Syndication, is an XML format designed to allow website content to be easily syndicated. The syndicated content can be integrated into other websites, or can be viewed by individuals via an assortment of desktop applications. Many sites syndicate content today using RSS 2.0. For example, the latest 4Guys articles are syndicated at http://aspnet.4guysfromrolla.com/rss/rss.aspx.
An RSS syndication feed has a format similar to the following:
< rss version="2.0">
<channel> <title>News by
Scott</title>
<link>http://www.example.com</link>
<description>Hear the news from
Scott.</description> |
In short, an RSS feed is made up of a set of <item>
elements, each of which represents some recent, syndicated piece of content. For
more information on RSS and the benefits of syndicating content, check out Syndicating Your Web
Site‘s Content with RSS; also consult the RSS
2.0 Specification.
For this example, we want to bind the set of content items to a DataList.
Therefore, set the XmlDataSource control‘s DataFile property
to the URL of the remote RSS 2.0 feed source (such as
http://aspnet.4guysfromrolla.com/rss/rss.aspx) and the
XPath property to /rss/channel/item. This XPath
statement instructs the XmlDataSource to return the set of
<item> elements, meaning the DataList bound to this
XmlDataSource will have one record created for each <item>
element in the specified RSS feed.
Next, add the DataList and configure its ItemTemplate to display
the <title>, <description>, and
<pubDate> of each content item, along with a link to read the
content (using the <link> element‘s value). The following
markup will work:
< asp:DataList ID="FeedList"
runat="server" DataSourceID="RSSFeedDataSource">
<ItemTemplate>
<h4>
<a
href=‘<%# XPath("link") %>‘>
<asp:Label
runat="server" ID="TitleLabel" Text=‘<%# XPath("title")
%>‘></asp:Label>
</a>
</h4>
<p>
<i>Published
<%#XPath("pubDate")%></i>
</p>
<p>
<asp:Label
runat="server" ID="DescriptionLabel" Text=‘<%#
XPath("description") %>‘></asp:Label>
</p>
<p>
[<a
href=‘<%# XPath("link") %>‘>Read More</a>]
</p>
<br />
</ItemTemplate> < /asp:DataList>
|
Note how the <# XPath("xpath") %> syntax is used
to grab a particular value from the current node bound to the DataList. Since
the DataList is bound to a set of <item> nodes, <%#
XPath("link") %> will return the value of the current
<item> node‘s <link> element.
After specifying the ItemTemplate, take a moment to view the
page in a browser. The following screenshot shows the output for the 4Guys RSS
feed.
An even easier approach to displaying RSS feeds in a web page is to use my free, open-source RssFeed control! See A Custom ASP.NET Server Control for Displaying RSS Feeds for more information...
The XPath("xpath") method allows us to bind a
particular value relative from the current XML node, but what if we want to get
back an entire nodeset and bind that to a nested data Web control? The
XPathSelect("xpath") method provides this functionality.
To illustrate the use of this method, let‘s create an example that displays a
receipt for a user‘s purchase, where the purchase details are spelled out in an
XML format. In the download available at the end of this article you‘ll find a
file named PO.xml in the project‘s App_Data folder.
This XML file (whose primary structure was found online in this
example XML file) contains information about a single order, and has the
following structure:
< Order
orderDate="orderDate"> <Customer>
<Name>name</Name>
<Cardnum>credit card
number</Cardnum> </Customer> |
To display a receipt, we need to display the customer‘s information, the
subtotal, tax, and total, and the set of items ordered. Since there can be a
variable number of items, this can best be displayed by using a nested data Web
control that‘s bound to the set of <Item> nodes.
To display the customer and price details, add a FormView and bind it to a
new XmlDataSource whose DataFile property set to
~/App_Data/PO.xml. Do not bother setting the XPath
property. Next, in the FormView‘s ItemTemplate, use the
XPath("xpath") method to display the the customer and
price details:
< asp:FormView ID="Receipt"
runat="server" DataSourceID="PODataSource">
<ItemTemplate>
<p><h3>RECEIPT</h3></p>
<p><b>Order Date:</b>
<asp:Label runat="server" ID="OrderDateLabel"
Text=‘<%#XPath("/Order/@orderDate")%>‘></asp:Label></p>
<p>
<b><u>Customer
Details:</u></b><br />
<b>Name:</b> <asp:Label
runat="server" ID="NameLabel"
Text=‘<%#XPath("/Order/Customer/Name")%>‘></asp:Label><br
/> <b>Card #:</b>
<asp:Label runat="server" ID="CardNumberLabel"
Text=‘<%#XPath("/Order/Customer/Cardnum")%>‘></asp:Label><br
/> </p>
|
Since the XmlDataSource control does not have an XPath value
specified, the <Order> node is what is bound to the FormView.
Therefore, to get the <Name> element value from the
<Customer> node, we need to use the XPath statement
/Order/Customer/Name. To get an attribute value -
orderDate, an attribute in the <Order> element -
prefix the attribute name with @ (i.e.,
/Order/@orderDate).
The above databinding syntax displays the customer and price details in the
FormView. We still need to display the set of <Item>s
associated with this order. To accomplish this, add a GridView control within
the FormView‘s ItemTemplate and assign its DataSource
property to the set of <Item> nodes using the following
syntax: <asp:GridView runat="server" ... DataSource=‘<#
XPathSelect("/Order/Manifest/Item") %>‘ ...>. Then, in the
GridView‘s <Columns> section, add a TemplateField for each of
the item details to display:
< asp:FormView ID="Receipt"
runat="server" DataSourceID="PODataSource">
<ItemTemplate> ... |
ASP.NET 2.0 offers a number of different data source controls for working
with different types of data. The SqlDataSource control, for example, is
designed to work with data in a relational database. As we saw in this article,
to work with XML data, use the XmlDataSource control. The XmlDataSource control
can access local or remote XML files, or can have raw XML data assigned to its
Data property. There‘s also the optional TransformFile
and XPath properties that can be set to transform or filter the
contents of the XML data.
Once the XmlDataSource control has been properly configured, it can be bound
to a data Web control. The contents of the XML returned by the XmlDataSource
control can be retrieved as scalar values using
XPath("xpath") or as nodesets using
XPathSelect("xpath"). See the download available at the
end of this article for the complete code explored in the two examples
above.
Happy Programming!
Accessing and Updating Data in ASP.NET: Retrieving XML Data with XmlDataSource Control
标签：des com http blog style class div img code java c
原文地址：http://www.cnblogs.com/happy-Chen/p/3699086.html
