C# 4 and .NET 4

916 ❘ ChaPTer 33 mAnipulAtinG xml
After executing this code, you end up with the same functionality as in the previous example, but there
is one additional book in the text box, The Case of the Missing Cookie (a soon-to-be classic). If you look
closely at the code, you can see that this is actually a fairly simple process. The first thing that you do is
create a new book element:
XmlElement newBook = doc.CreateElement("book");
CreateElement() has three overloads that allow you to specify the following:
➤
➤
➤
The element name
The name and namespace URI
The prefix, localname, and namespace
Once the element is created, you need to add attributes:
newBook.SetAttribute("genre","Mystery");
newBook.SetAttribute("publicationdate","2001");
newBook.SetAttribute("ISBN","123456789");
Now that you have the attributes created, you need to add the other elements of a book:
XmlElement newTitle = doc.CreateElement("title");
newTitle.InnerText = "The Case of the Missing Cookie";
newBook.AppendChild(newTitle);
Once again, you create a new XmlElement-based object (newTitle). Then you set the InnerText property
to the title of our new classic and append the element as a child to the book element. You repeat this for
the rest of the elements in this book element. Note that you add the name element as a child to the author
element. This will give you the proper nesting relationship, as in the other book elements.
Finally, you append the newBook element to the doc.DocumentElement node. This is the same level as all of
the other book elements. You have now updated an existing document with a new element.
The last thing to do is to write the new XML document to disk. In this example, you create a new
XmlTextWriter and pass it to the WriteContentTo() method. WriteContentTo() and WriteTo() both
take an XmlTextWriter as a parameter. WriteContentTo() saves the current node and all of its children
to the XmlTextWriter, whereas WriteTo() just saves the current node. Because doc is an XmlDocumentbased
object, it represents the entire document and so
that is what is saved. You could also use the Save()
method. It will always save the entire document.
Save() has four overloads. You can specify a string
with the filename and path, a Stream-based object,
a TextWriter-based object, or an XmlWriter-based
object.
You also call the Close() method on
XmlTextWriter to flush the internal buffers and
close the file.
Figure 33-1 shows what you get when you run this
example. Notice the new entry at the bottom of
the list.
Earlier in the chapter, you saw how to create a
document using the XmlTextWriter class. You can also use XmlDocument. Why would you use one in
preference to the other If the data that you want streamed to XML is available and ready to write, then
the XmlTextWriter class is the best choice. However, if you need to build the XML document a little at a
time, inserting nodes into various places, then creating the document with XmlDocument might be the better
choice. You can accomplish this by changing the following line:
doc.Load("books.xml");
figure 33-1
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