Table 10.2 demonstrates a few key properties and methods of the XmlDocument class.

Note that the CreateElement() and CreateAttribute() methods create the specified structures but do not specifically add them to the document.

Use the XmlNode.AppendNode(), XmlNode.InsertBefore(), or XmlNode.InsertAfter() method to add a node and the XmlElement.SetAttributeNode() method to set an attribute to a node.

Table 10.2: Selected Members of the XmlDocument Class

Member	Type	Description	Example	Example
				Description
DocumentElement	Property	Sets or gets the	MessageBox.Show	Displays the root
		root XML	(doc.DocumentElement);	element for an
		element for the		XmlDocument
		document		named doc
CreateAttribute	Method	Creates a new	doc.CreateAttribute	Creates a new
		attribute for an	(name) ("type");	attribute but
		element with		does not add it
		the specified
		name
CreateElement	Method	Creates a new	doc.CreateElement	Creates a new
(name)		element	("question");	element but
				does not add it
Load(filename)	Method	Loads an XML	doc.Load	Loads the
		document from	("myStuff.xml");	specified file into
		the given file		the document
		name
LoadXml	Method	Interprets a	doc.LoadXml	Loads the text
(xmlString)		string value as	("<simpleXml>this is	value as a
		XML	simple</simpleXml>");	simple XML
				document
Save	Method	Saves the	doc.Save	Saves thecurrent
(filename)		document to	("myStuff.xml");	document to a
		the specified		file named
		file		myStuff.xml

Reading an Existing XML Document

The only way to make sense of all this information is to build a program that puts it to use. The XML Viewer program will help you see how exactly C# reads an XML document and how to get around in it. The XML Viewer is more than a programming exercise. It is a tool you can use to analyze and explore the structure of any XML document. After you see how it describes the data in an XML document, you will be ready to get inside the engine and see how the program does its work. Figure 10.7 illustrates the XML Viewer as it first loads the quiz document.

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Figure 10.7: The starting node is named xml, but it isn’t very interesting.

The root node is the xml tag itself. It usually provides some background information, but it doesn’t have any children and doesn’t contain a lot of other data. To get to the interesting parts of the file, you click the Next Sibling button (see Figure 10.8).

Figure 10.8: The test node has a lot more information. (Almost too much!)

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The test node is much more interesting. All the interesting data in the quiz file was somehow related to the test node, so it isn’t surprising that the test node shows much more information. All the screen elements in the XML Viewer program describe properties of the current node. The Parent button refers to the test node’s parent node, which is the document itself. I disabled the Parent button in this particular case because the document is the top layer. The node field refers to the Name property of the current node. In this case, the name of the current node is test. The value label refers to the Value property of the current node. You might be surprised that the test node has no value at all. That is because all the information of the test is actually stored in its children. As you will see, the InnerText property often turns out to be more useful than the Value property.

The InnerXml property returns all the XML associated with the current node. When test is the current node, all the XML between the <test> and </test> tags in the original XML show up as the InnerXml property. The InnerText property simply strips out the XML tags from the InnerXml property and returns the resulting text. Notice that the Next Sibling button is disabled because the program has detected that the test element does not have a next sibling.

A node can have several child nodes, as you can see from the test node. In this particular file, the test has three problems, and you can see a list box with three problem nodes. To view one of the child nodes, double−click it. I chose the first problem, which results in Figure 10.9.

Figure 10.9: I have clicked the first problem, and the viewer is now looking at the problem node.

All the screen elements have changed to reflect that the problem node has the focus. The test node is now listed as the parent node, and you can click the button to return to the parent node. (That’s why I made the parent node a button instead of a label.) The problem node still doesn’t have a value because it is mainly a container for other nodes. You can see that the InnerXml and InnerText properties have narrowed their scope considerably. Also, the list of ChildNodes shows the question, possible answers, and correct answer. The Next Sibling button is activated because this question has siblings. Click the Next Sibling button a couple times until it becomes disabled. It will do so at the last question, which gives you a screen like Figure 10.10.

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Figure 10.10: Now the viewer is pointed at the last child of the test node.

It’s time to investigate the children of the problem node. Click the first child (the question), and you will see something like Figure 10.11.

Figure 10.11: You might be surprised that there still isn’t anything useful in the value field.

It would seem as though the question is the lowest level of the XML document, but it isn’t. The InnerText and InnerXml of the question (and all its siblings) are useful information, but you will see

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that the question has one child, marked as #text. Not until you get to the #text node do you finally have actual data in the value field. The XML Viewer program is particularly interesting because it can be used to analyze any legal XML document. This points out one of XML’s advantages. The format of the data describes the data’s meaning, so a program can work with data in a new format with some hope of deciphering it.

Figure 10.12 illustrates how the .NET framework sees the quiz document.

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Figure 10.12: This diagram more accurately reflects how .NET sees an XML document.

Trick

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