C# 4 and .NET 4

908 ❘ ChaPTer 33 mAnipulAtinG xml
In the while loop, you use MoveToContent() to find each node of type XmlNodeType.Element with the
name title. You use the EOF property of the XmlTextReader as the loop condition. If the node is not of
type Element or not named title, the else clause will issue a Read() method to move to the next node.
When you find a node that matches the criteria, you add the result of a ReadElementString() to the list
box. This should leave you with just the book titles in the list box. Note that you don’t have to issue a
Read() call after a successful ReadElementString() because ReadElementString() consumes the entire
Element and positions you on the next node.
If you remove && rdr.Name==“title” from the if clause, you will have to catch the XmlException
when it is thrown. If you look at the data file, you will see that the first element that MoveToContent()
will find is the element. Because it is an element, it will pass the check in the if statement.
However, because it does not contain a simple text type, it will cause ReadElementString() to raise an
XmlException. One way to work around this is to put the ReadElementString() call in a function of its
own. Then, if the call to ReadElementString() fails inside this function, you can deal with the error and
return to the calling function.
Go ahead and do this; call this new method LoadTextBox() and pass in the XmlTextReader as a
parameter. This is what the LoadTextBox() method looks like with these changes:
private void LoadTextBox(XmlReader reader)
{
try
{
richTextBox1.AppendText (reader.ReadElementString() + "\r\n");
}
// if an XmlException is raised, ignore it.
catch(XmlException er){}
}
This section from the previous example:
if (tr.MoveToContent() == XmlNodeType.Element && tr.Name == "title")
{
richTextBox1.AppendText(tr.ReadElementString() + "\r\n");
}
else
{
//otherwise move on
tr.Read();
}
will have to be changed to the following:
if (tr.MoveToContent() == XmlNodeType.Element)
{
LoadTextBox(tr);
}
else
{
//otherwise move on
tr.Read();
}
After running this example, the results should be the same as before. What you are seeing is that there
is more than one way to accomplish the same goal. This is where the flexibility of the classes in the
System.Xml namespace starts to become apparent.
The XmlReader can also read strongly typed data. There are several ReadElementContentAs methods, such
as ReadElementContentAsDouble, ReadElementContentAsBoolean, and so on. The following example
shows how to read in the values as a decimal and do some math on the value. In this case, the value from the
price element is increased by 25 percent:
www.it-ebooks.info