Use XML writer classes to create XML documents directly to disk files
XML documents are first and foremost text files, so writing them doesn't need to be complicated. Any set of functions that lets you create and edit a text file is fine for persisting XML data. However, XML documents aren't ordinary text files because you need to ensure that XML files are well formed and that they follow the correct schema. In particular, when you use a standard (not made-to-measure) API, errors can easily slip into the code, such as missing closing tags, mismatched tag names, and unquoted attribute values.
You can programmatically write an XML file by using the methods of the XML Document Object Model (DOM). If you choose this approach, however, you're required to create in memory the entire tree of nodes and attributes and then persist the tree in a single shot to the disk. You use the XML DOM's methods to build the tree, which guarantees that the document is well formed but consumes excessive processing resources. This approach treats a disk-based XML document as it would a file in which a particular instance of an XML DOM object is persisted. The XML DOM doesn't accommodate any form of progressive dumping. In other words, the XML DOM is good for in-memory processing and searching but not for XML input and output.
In previous issues, I reviewed the XML reader classes and how to use them to read XML content from disk files. Although XML readers are the preferred way to read XML data in the .NET architecture, the XML writer classes are the most natural way to create XML documents directly to disk files.
The base and abstract .NET class that contains the main functionality of XML writers is XmlWriter. But XmlTextWriter is likely the base class that you'll use in your XML applications. This class offers several functions. It lets you set the namespace and the tag prefix, choose the character set, and define whether an indentation is necessary, which character to use, and how large you want the character to be.
XmlTextReader uses a stream-based interface and offers specialized methods to help you write specific XML nodes and typed attributes. You create an instance of the XmlTextWriter class with the following syntax:
XmlTextWriter xtw = new XmlTextWriter(fileName, null);
The first argument is the fully qualified name of the XML file you want to create. The second argument identifies the character set you choose. If you don't specify the character set, the class defaults to the UTF-8 character set.
After you have a valid instance of the XmlTextWriter class, you can adapt a few of its settings to your needs. In particular, you can require that a newline character be appended at the end of each node. Note that the definition of a node includes the open tag, any attribute, the text, and the closing tag. You use the following code to set the automatic newline character:
xtw.Formatting = Formatting.Indented;
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