Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

Table 5-2: Methods of the XmlDocument ClassMethodDescriptionwriter.As you can see, the XmlDocument class has a lot of methods that create and returninstances of node objects. In the .NET Framework, all the objects that represent a nodetype (Comment, Element, Attribute, and so on) do not have any publicly usableconstructors. For this reason, you must resort to the corresponding method.How can the XmlDocument class create and return instances of other node objects ifno public constructor for them is available? The trick is that node classes mark theirconstructors with the internal modifier (Friend in Microsoft Visual Basic). The internalkeyword restricts the default visibility of a type method or property to the boundaries ofthe assembly. The internal keyword works on top of other modifiers like public andprotected. XmlDocument and other node classes are all defined in the System.Xmlassembly, which ensures the effective working of factory methods. The followingpseudocode shows the internal architecture of a factory method:public virtual XmlXXX CreateXXX( params ){return new XmlXXX ( params );}NoteWhen the node class is XmlDocument, the methods WriteTo andWriteContentTo happen to produce the same output, although theydefinitely run different code. WriteTo is designed to persist the entirecontents of the node, including the markup for the node, attributes,and children. WriteContentTo, on the other hand, walks its waythrough the collection of child nodes and persists the contents ofeach using WriteTo. Here's the pseudocode:void WriteContentTo(XmlWriter w) {foreach(XmlNode n in this)n.WriteTo(w);}A Document node is a kind of super root node, so the loop on allchild nodes begins with the actual root node of the XML document.In this case, WriteTo simply writes out the entire contents of thedocument but the super root node has no markup. As a result, thetwo methods produce the same output for the XmlDocument class.Events of the XmlDocument ClassTable 5-3 lists the events that the XmlDocument class fires under the following specificconditions: when the value of a node (any node) is being edited, and when a node isbeing inserted into or removed from the document.Table 5-3: Events of the XmlDocument ClassEventsNodeChanging,NodeChangedNodeInserting,NodeInsertedDescriptionThe Value property of a node belonging to thisdocument is about to be changed or has beenchanged already.A node is about to be inserted into another node175