QAbstractXmlReceiver Class

The QAbstractXmlReceiver class provides a callback interface for transforming the output of a QXmlQuery. More...

Header: #include <QAbstractXmlReceiver>
qmake: QT += xmlpatterns
Since: Qt 4.4
Inherited By:

QXmlSerializer

Note: All functions in this class are reentrant.

Public Functions

QAbstractXmlReceiver()
virtual ~QAbstractXmlReceiver()
virtual void atomicValue(const QVariant &value) = 0
virtual void attribute(const QXmlName &name, const QStringRef &value) = 0
virtual void characters(const QStringRef &value) = 0
virtual void comment(const QString &value) = 0
virtual void endDocument() = 0
virtual void endElement() = 0
virtual void endOfSequence() = 0
virtual void namespaceBinding(const QXmlName &name) = 0
virtual void processingInstruction(const QXmlName &target, const QString &value) = 0
virtual void startDocument() = 0
virtual void startElement(const QXmlName &name) = 0
virtual void startOfSequence() = 0

Detailed Description

The QAbstractXmlReceiver class provides a callback interface for transforming the output of a QXmlQuery.

QAbstractXmlReceiver is an abstract base class that provides a callback interface for receiving an XQuery sequence, usually the output of an QXmlQuery, and transforming that sequence into a structure of your choosing, usually XML. Consider the example:


  QXmlQuery query;
  query.setQuery("doc('index.html')/html/body/p[1]");

  QXmlSerializer serializer(query, myOutputDevice);
  query.evaluateTo(&serializer);

First it constructs a query that gets the first paragraph from document index.html. Then it constructs an XML serializer with the query and myOutputDevice (Note the serializer is an XML receiver, ie a subclass of QAbstractXmlReceiver). Finally, it evaluates the query, producing an ordered sequence of calls to the serializer's callback functions. The sequence of callbacks transforms the query output to XML and writes it to myOutputDevice.

Although the example uses QXmlQuery to produce the sequence of callbacks to functions in QAbstractXmlReceiver, you can call the callback functions directly as long as your sequence of calls represents a valid XQuery sequence.

XQuery Sequences

An XQuery sequence is an ordered collection of zero, one, or many items. Each item is either an atomic value or a node. An atomic value is a simple data value.

There are six kinds of nodes.

  • An Element Node represents an XML element.
  • An Attribute Node represents an XML attribute.
  • A Document Node represents an entire XML document.
  • A Text Node represents character data (element content).
  • A Processing Instruction Node represents an XML processing instruction, which is used in an XML document to tell the application reading the document to perform some action. A typical example is to use a processing instruction to tell the application to use a particular XSLT stylesheet to display the document.
  • And a Comment node represents an XML comment.

The sequence of nodes and atomic values obeys the following rules. Note that Namespace Node refers to a special Attribute Node with name xmlns.

  • Each node appears in the sequence before its children and their descendants appear.
  • A node's descendants appear in the sequence before any of its siblings appear.
  • A Document Node represents an entire document. Zero or more Document Nodes can appear in a sequence, but they can only be top level items (i.e., a Document Node can't be a child of another node.
  • Namespace Nodes immediately follow the Element Node with which they are associated.
  • Attribute Nodes immediately follow the Namespace Nodes of the element with which they are associated, or...
  • If there are no Namespace Nodes following an element, then the Attribute Nodes immediately follow the element.
  • An atomic value can only appear as a top level item, i.e., it can't appear as a child of a node.
  • Processing Instruction Nodes do not have children, and their parent is either a Document Node or an Element Node.
  • Comment Nodes do not have children, and their parent is either a Document Node or an Element Node.

The sequence of nodes and atomic values is sent to an QAbstractXmlReceiver (QXmlSerializer in the example above) as a sequence of calls to the receiver's callback functions. The mapping of callback functions to sequence items is as follows.

For a complete explanation of XQuery sequences, visit XQuery Data Model.

See also W3C XQuery 1.0 and XPath 2.0 Data Model (XDM), QXmlSerializer, and QXmlResultItems.

Member Function Documentation

QAbstractXmlReceiver::QAbstractXmlReceiver()

Constructs an abstract xml receiver.

[virtual] QAbstractXmlReceiver::~QAbstractXmlReceiver()

Destroys the xml receiver.

[pure virtual] void QAbstractXmlReceiver::atomicValue(const QVariant &value)

[pure virtual] void QAbstractXmlReceiver::attribute(const QXmlName &name, const QStringRef &value)

[pure virtual] void QAbstractXmlReceiver::characters(const QStringRef &value)

[pure virtual] void QAbstractXmlReceiver::comment(const QString &value)

[pure virtual] void QAbstractXmlReceiver::endDocument()

[pure virtual] void QAbstractXmlReceiver::endElement()

[pure virtual] void QAbstractXmlReceiver::endOfSequence()

[pure virtual] void QAbstractXmlReceiver::namespaceBinding(const QXmlName &name)

[pure virtual] void QAbstractXmlReceiver::processingInstruction(const QXmlName &target, const QString &value)

[pure virtual] void QAbstractXmlReceiver::startDocument()

[pure virtual] void QAbstractXmlReceiver::startElement(const QXmlName &name)

[pure virtual] void QAbstractXmlReceiver::startOfSequence()