Reading XML Files Directly - Page 1
       by kirupa  |  11 May 2007

There are two ways to read an XML file. One way, which I covered in an earlier tutorial, is when you read the XML file sequentially and parse the information as you see it. The second approach, which I cover in this tutorial, is where you load the entire XML file into  memory and access the information directly. In the following pages, let's learn how to do that.

Concise Blog Post

An abbreviated version of this tutorial featuring the same code but with a focus more on code readability can be found on the kirupaBlog by clicking here.

Let's look at some XML data that we will be using in this tutorial:

Example of XML Document 

In this tutorial, we are going to be picking out specific pieces of data from the above XML file, so it is beneficial to look at the structure of not only this XML file, but XML files in general.

The XML Structure
An XML file is essentially a tree with various branches and leaves commonly known as nodes and values. Our above XML data is no exception. The following diagram shows one way of representing our sample XML data:

XML Data

Think of each box in the above image as a node. We have our main root node called Books, and that root node has four child nodes called Book. The Book node contains the ISBN information, and information stored directly on the node is called an attribute. You can also store information in your child nodes, and the book's title and author information is stored in child nodes aptly called title and author.

This type of a hierarchy, like all XML data, is essentially a tree. In the computer world, trees are great because they help you to categorize information all the way from a broad overview at the top of the tree to the details at the leaves. From the above data, you can easily see that the parent node (Books) sets the agenda for what the child nodes (Book, Title, Author) will follow.

Reading XML Directly
Now that have a vague idea of what an XML file looks like and what the interesting features of an XML file are, let's look at the code for reading our XML file in C#:

XmlDocument doc = new XmlDocument();
XmlNodeList bookList = doc.GetElementsByTagName("Book");
foreach (XmlNode node in bookList)
XmlElement bookElement = (XmlElement) node;
string title = bookElement.GetElementsByTagName("title")[0].InnerText;
string author = bookElement.GetElementsByTagName("author")[0].InnerText;
string isbn = "";
if (bookElement.HasAttributes)
isbn = bookElement.Attributes["ISBN"].InnerText;
Console.WriteLine("{0} ({1}) is written by {2}\n", title, isbn, author);

If you create a new C# Console Application, paste the above code inside your Main method, resolve the missing System.XML namespace (see below if you are not sure how to do that), and run your program by pressing Ctrl + F5. You should see your Console window display all of the information stored in the XML file:

Console output

[ the XML information displayed on your screen ]

If you receive an error such as missing namespace, the next section addresses that.

Resolving Missing Namespaces
Be sure to add the System.XML namespace. You can do that automatically by right-clicking on any of the XML-specific (uncolored) classes in your code such as XmlDocument, XmlNodeList, etc. and selecting Resolve | using System.Xml:

Resolve the unknown classes using Visual Studio itself.

[ resolve missing namespaces by right-clicking on unrecognized classes ]

This application isn't pretty, but it shows you how to read data from the XML file. Let's now go through and look at each line of code and figure out how it helps you to read the XML data, and more importantly, you can integrate this code and what you will learn in subsequent pages into your own, more useful applications.

Speaking of subsequent pages, in the next page, you will learn how the code works.

Onwards to the next page!

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