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# QAbstractXmlReceiver Class Reference
[QtXmlPatterns module]

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

     #include <QAbstractXmlReceiver>

Inherits QSharedData.

Inherited by QPatternist::DocumentContentValidator, QPatternist::DocumentProjector, QPatternist::NodeBuilder, QPatternist::OutputValidator, and QXmlSerializer.

Note: All the functions in this class are reentrant.

This class was introduced in Qt 4.4.

- List of all members, including inherited members

### Public Functions

- QAbstractXmlReceiver ()
- virtual ~QAbstractXmlReceiver ()
- virtual void atomicValue ( const QVariant & value ) = 0
- virtual void attribute ( const QXmlName & name, const QString & value ) = 0
- virtual void characters ( const QString & value ) = 0
- virtual void comment ( const QString & value ) = 0
- virtual void endDocument () = 0
- virtual void endElement () = 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

## 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]");

     QXmlSerializerPointer serializer(new QXmlSerializer(query, myOutputDevice));
     query.evaluateToReceiver(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.
- And a Comment node represents an XML comment.

The order of nodes and atomic values in a sequence 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.

The sequence of nodes and atomic values is sent to an XML receiver (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.

- startDocument() and endDocument() are called for each Document Node in the sequence. endDocument() is not called until all the Document Node's children have appeared in the sequence.
- startElement() and endElement() are called for each Element Node. endElement() is not called until all the Element Node's children have appeared in the sequence.
- attribute() is called for each Attribute Node.
- comment() is called for each Comment Node.
- characters() is called for each Text Node.
- processingInstruction() is called for each Processing Instruction Node.
- namespaceBinding() is called for each Namespace Node.
- atomicValue() is called for each atomic value.

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 a QAbstractXmlReceiver instance.

### QAbstractXmlReceiver::~QAbstractXmlReceiver () `[virtual]`

Destructs this QAbstractXmlReceiver.

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

Signals an atomic value.

The caller guarantees that value is valid.

See also QVariant::isValid().

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

Signals an attribute by name name, and value value.

The caller guarantees name is a valid name.

### void QAbstractXmlReceiver::characters ( const QString & value ) `[pure virtual]`

Signals a text node with content value. Adjacent text nodes may not occur.

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

Signals a comment whose value is value.

The caller guarantees that value does not contain the string "--".

### void QAbstractXmlReceiver::endDocument () `[pure virtual]`

Signals the end of a document node.

### void QAbstractXmlReceiver::endElement () `[pure virtual]`

Signals the end of the most recently received element.

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

Signals a namespace binding. In name, the namespace URI is the namespace URI, and the local name is the prefix the binding binds to.

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

Signals a processing instruction with target (the name) and content value.

The caller guarantees that value does not contain the string "?>".

The caller guarantees target is a valid name, that the prefix and namespace URI is empty, and that the local name is the target.

### void QAbstractXmlReceiver::startDocument () `[pure virtual]`

Signals the start of a document node.

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

Signals the start of an element by name name.

The caller guarantees name is a valid name.