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3
Writing XML Files
We can use the XmlWriter class to write XML files. It allows you to write XML text into a stream and then save it into an xml file.
using System.Xml;
public class Program
{
public static void Main()
{
XmlWriterSettings settings = new XmlWriterSettings();
settings.Indent = true;
XmlWriter writer = XmlWriter.Create("Products.xml", settings);
writer.WriteStartDocument();
writer.WriteComment("This file is generated by the program.");
writer.WriteStartElement("Product");
writer.WriteAttributeString("ID", "001");
writer.WriteAttributeString("Name", "Soap");
writer.WriteElementString("Price", "10.00");
writer.WriteStartElement("OtherDetails");
writer.WriteElementString("BrandName", "X Soap");
writer.WriteElementString("Manufacturer", "X Company");
writer.WriteEndElement();
writer.WriteEndDocument();
writer.Flush();
writer.Close();
}
}
We first import the System.Xml namespace. We use the XmlWriterSettings class to create a setting for the XmlWriter that we will use. We dictated the program to use proper indention when writing the xml by using this settings. We then create an XmlWriter object by calling the XmlWriter.Create method and supplying the filename and the XmlWriterSettings object.Using the XmlWriter class, we can write our xml. We first use the XmlWriter.WriteStartDocument() method which writes the xml declaration you find on the top of most xml files. Next we create a sample comment using teh XmlWriter.WriteComment() method. To write an Xml Element, we use the XmlWriter.WriteStartElement() and supply the name of the element as the argument. The XmlWriter.WriteStartElement() must be paired with XmlWriter.WriteEndElement which writes the closing tag of that element. We now create some attributes for the element using the XmlWriter.WriteAttributeString() method and supply the name and the value for that attribute.
We used the XmlWriter.WriteElementString() method with a name and a value as the arguments to write an element that is wrapping a value. We then nested another element inside the Products element by writing one more set of XmlWriter.WriteStartElement() and XmlWriter.WriteEndElement() . Inside it, we add two more elements that contain values. To mark the end of the document, we simly call the XmlWriter.WriteEndDocument() method.
Finally, we used the XmlWriter.Flush() method to clean the contents of the stream and the XmlWriter.Close() method to save the file and stop the program from using it.
The above code will produce the following XML file contents:
<?xml version="1.0" encoding="utf-8"?>
<!--This file is generated by the program.-->
<Product ID="001" Name="Soap">
<Price>10.00</Price>
<OtherDetails>
<BrandName>X Soap</BrandName>
<Manufacturer>X Company</Manufacturer>
</OtherDetails>
</Product>
Reading XML FilesTo read xml files, we can use the XmlReader class. We will use the XML file we created earlier to assign the values into variables. Note that we will simply use variables for storing the values from the XML. A better approach is by creating a Products class the follows the heirarchy of the XML file. The following program demonstrates the use of XmlReader class.
using System;
using System.Xml;
public class Program
{
public static void Main()
{
XmlReader reader = XmlReader.Create("Products.xml");
while (reader.Read())
{
if (reader.NodeType == XmlNodeType.Element
&& reader.Name == "Product")
{
Console.WriteLine("ID = " + reader.GetAttribute(0));
Console.WriteLine("Name = " + reader.GetAttribute(1));
while (reader.NodeType != XmlNodeType.EndElement)
{
reader.Read();
if (reader.Name == "Price")
{
while (reader.NodeType != XmlNodeType.EndElement)
{
reader.Read();
if (reader.NodeType == XmlNodeType.Text)
{
Console.WriteLine("Price = {0:C}", Double.Parse(reader.Value));
}
}
reader.Read();
} //end if
if (reader.Name == "OtherDetails")
{
while (reader.NodeType != XmlNodeType.EndElement)
{
reader.Read();
if (reader.Name == "BrandName")
{
while (reader.NodeType != XmlNodeType.EndElement)
{
reader.Read();
if (reader.NodeType == XmlNodeType.Text)
{
Console.WriteLine("Brand Name = " + reader.Value);
}
}
reader.Read();
} //end if
if (reader.Name == "Manufacturer")
{
while (reader.NodeType != XmlNodeType.EndElement)
{
reader.Read();
if (reader.NodeType == XmlNodeType.Text)
{
Console.WriteLine("Manufacturer = " + reader.Value);
}
}
} //end if
}
} //end if
} //end while
} //end if
} //end while
}
}
Output:
ID = 001 Name = Soap Price = $10.00 Brand Name = X Soap Manufacturer = X Company
There are other ways to read Xml files but this tutorial will focus on using the XmlReader class. First, we create an XmlReader object using the static method Create and passing the filename of the XML file that will be read.
XmlReader reader = XmlReader.Create("Products.xml");
We now enter a loop that will read each node in the xml file including the whitespaces. We use the XmlReader.Read() that returns true if there are more nodes to read or false if there is no more or if it reaches the end of the file.
We first look at the Product element. The first condition checks if the current node read by the reader is an element and has a name of "Product". The XmlNodeTpe enumeration list all the possible node types including whitespaces, text and comments. We then show the values of the attributes of the product element:
Console.WriteLine("ID = " + reader.GetAttribute(0));
Console.WriteLine("Name = " + reader.GetAttribute(1));
The GetAttribute() method gets the values of the attribute of an element. The number indicates what attribute you are getting. 0 indicates the first attribute and 1 indicates the second attribute.
You will now encounter a series of nested while and if statements. The first while loop will search for the Price element. The Read() method will go to the next node while it is not an end element. If the type of the node is a text, we display it on the screen.
Basically, reading xml files using XmlReader requires you to look carefully at the structure of your XML.
Edited by rueleonheart, 13 August 2010 - 04:42 AM.
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