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

Table 6-4: XPathNavigator Move MethodsMethodMoveToNextMoveToNextAttributeMoveToNextNamespaceMoveToParentMoveToPreviousMoveToRootDescriptionnamespace node is the prefix.Moves to the next sibling of the current node.Moves to the next attribute of the current node.Moves to the next namespace in the currentelement node.Moves to the parent of the current node.Moves to the previous sibling of the currentnode.Moves to the root node of the document.The MoveTo method attempts to synchronize the current instance of theXPathNavigator object with another instance. MoveTo returns true or false dependingon the success or failure of the operation. Note that the synchronization always fails ifthe two navigators are actually implemented through different and incompatible classes.Two navigators have different implementations if the other navigator can't be cast to thecurrent type.Consider the following pseudocode:public bool MoveTo(XPathNavigator other){InternalXPathNavigator nav = other as InternalXPathNavigator;if (nav == null)return false;}⋮In C#, the as operator behaves like a cast except that, when the conversion fails, itreturns null rather than raising an exception. In the preceding pseudocode, theInternalXPathNavigator class represents the actual (and internal) navigator class yougot from the document's CreateNavigator method. Each XPathenabled document classactually instantiates a custom navigator class and returns that class when you call itsCreateNavigator method.The MoveTo method also might fail when the two navigators share the sameimplementation but point to different document instances. What happens in this case,however, depends on the specific implementation. In particular, MoveTo fails when thedocument class is XmlDocument or XmlDataDocument, but not when the underlyingdata object is an instance of XPathDocument.Namespace Node NavigationAs you might have noticed in Table 6-4, there are three types of move methods: forelement, attribute, and namespace nodes. Calling the wrong method on a nodecauses the whole operation to fail, and there is no change in the position of thenavigator. Only MoveTo and MoveToRoot can be called on any node, irrespective of221