- Qt 6.9
- Qt 5 Core Compatibility APIs
- C++ Classes
- QXmlDefaultHandler
- Qt 6.9.1 Reference Documentation

# QXmlDefaultHandler Class

The QXmlDefaultHandler class provides a default implementation of all the XML handler classes. More...

Header: | `#include <QXmlDefaultHandler>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Core5Compat)` `target_link_libraries(mytarget PRIVATE Qt6::Core5Compat)`
qmake: | `QT += core5compat`
Inherits: | QXmlContentHandler, QXmlErrorHandler, QXmlDTDHandler, QXmlEntityResolver, QXmlLexicalHandler, and QXmlDeclHandler

- List of all members, including inherited members

Note: All functions in this class are reentrant.

## Public Functions

| QXmlDefaultHandler()
virtual | ~QXmlDefaultHandler()

## Reimplemented Public Functions

virtual bool | attributeDecl(const QString &eName, const QString &aName, const QString &type, const QString &valueDefault, const QString &value) override
virtual bool | characters(const QString &ch) override
virtual bool | comment(const QString &ch) override
virtual bool | endCDATA() override
virtual bool | endDTD() override
virtual bool | endDocument() override
virtual bool | endElement(const QString &namespaceURI, const QString &localName, const QString &qName) override
virtual bool | endEntity(const QString &name) override
virtual bool | endPrefixMapping(const QString &prefix) override
virtual bool | error(const QXmlParseException &exception) override
virtual QString | errorString() const override
virtual bool | externalEntityDecl(const QString &name, const QString &publicId, const QString &systemId) override
virtual bool | fatalError(const QXmlParseException &exception) override
virtual bool | ignorableWhitespace(const QString &ch) override
virtual bool | internalEntityDecl(const QString &name, const QString &value) override
virtual bool | notationDecl(const QString &name, const QString &publicId, const QString &systemId) override
virtual bool | processingInstruction(const QString &target, const QString &data) override
virtual bool | resolveEntity(const QString &publicId, const QString &systemId, QXmlInputSource *&ret) override
virtual void | setDocumentLocator(QXmlLocator *locator) override
virtual bool | skippedEntity(const QString &name) override
virtual bool | startCDATA() override
virtual bool | startDTD(const QString &name, const QString &publicId, const QString &systemId) override
virtual bool | startDocument() override
virtual bool | startElement(const QString &namespaceURI, const QString &localName, const QString &qName, const QXmlAttributes &atts) override
virtual bool | startEntity(const QString &name) override
virtual bool | startPrefixMapping(const QString &prefix, const QString &uri) override
virtual bool | unparsedEntityDecl(const QString &name, const QString &publicId, const QString &systemId, const QString &notationName) override
virtual bool | warning(const QXmlParseException &exception) override

## Detailed Description

This class gathers together the features of the specialized handler classes, making it a convenient starting point when implementing custom handlers for subclasses of QXmlReader, particularly QXmlSimpleReader. The virtual functions from each of the base classes are reimplemented in this class, providing sensible default behavior for many common cases. By subclassing this class, and overriding these functions, you can concentrate on implementing the parts of the handler relevant to your application.

The XML reader must be told which handler to use for different kinds of events during parsing. This means that, although QXmlDefaultHandler provides default implementations of functions inherited from all its base classes, we can still use specialized handlers for particular kinds of events.

For example, QXmlDefaultHandler subclasses both QXmlContentHandler and QXmlErrorHandler, so by subclassing it we can use the same handler for both of the following reader functions:

         xmlReader.setContentHandler(handler);
         xmlReader.setErrorHandler(handler);

Since the reader will inform the handler of parsing errors, it is necessary to reimplement QXmlErrorHandler::fatalError() if, for example, we want to stop parsing when such an error occurs:

     bool Handler::fatalError (const QXmlParseException & exception)
     {
         qWarning() << "Fatal error on line" << exception.lineNumber()
                    << ", column" << exception.columnNumber() << ':'
                    << exception.message();

         return false;
     }

The above function returns `false`, which tells the reader to stop parsing. To continue to use the same reader, it is necessary to create a new handler instance, and set up the reader to use it in the manner described above.

It is useful to examine some of the functions inherited by QXmlDefaultHandler, and consider why they might be reimplemented in a custom handler. Custom handlers will typically reimplement QXmlContentHandler::startDocument() to prepare the handler for new content. Document elements and the text within them can be processed by reimplementing QXmlContentHandler::startElement(), QXmlContentHandler::endElement(), and QXmlContentHandler::characters(). You may want to reimplement QXmlContentHandler::endDocument() to perform some finalization or validation on the content once the document has been read completely.

See also QXmlDTDHandler, QXmlDeclHandler, QXmlContentHandler, QXmlEntityResolver, QXmlErrorHandler, and QXmlLexicalHandler.

## Member Function Documentation

### QXmlDefaultHandler::QXmlDefaultHandler()

Constructs a handler for use with subclasses of QXmlReader.

### `[virtual noexcept]` QXmlDefaultHandler::~QXmlDefaultHandler()

Destroys the handler.

### `[override virtual]` bool QXmlDefaultHandler::attributeDecl(const QString &eName, const QString &aName, const QString &type, const QString &valueDefault, const QString &value)

Reimplements: QXmlDeclHandler::attributeDecl(const QString &eName, const QString &aName, const QString &type, const QString &valueDefault, const QString &value).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::characters(const QString &ch)

Reimplements: QXmlContentHandler::characters(const QString &ch).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::comment(const QString &ch)

Reimplements: QXmlLexicalHandler::comment(const QString &ch).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::endCDATA()

Reimplements: QXmlLexicalHandler::endCDATA().

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::endDTD()

Reimplements: QXmlLexicalHandler::endDTD().

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::endDocument()

Reimplements: QXmlContentHandler::endDocument().

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::endElement(const QString &namespaceURI, const QString &localName, const QString &qName)

Reimplements: QXmlContentHandler::endElement(const QString &namespaceURI, const QString &localName, const QString &qName).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::endEntity(const QString &name)

Reimplements: QXmlLexicalHandler::endEntity(const QString &name).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::endPrefixMapping(const QString &prefix)

Reimplements: QXmlContentHandler::endPrefixMapping(const QString &prefix).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::error(const QXmlParseException &exception)

Reimplements: QXmlErrorHandler::error(const QXmlParseException &exception).

This reimplementation does nothing.

### `[override virtual]` QString QXmlDefaultHandler::errorString() const

Reimplements: QXmlContentHandler::errorString() const.

Returns the default error string.

### `[override virtual]` bool QXmlDefaultHandler::externalEntityDecl(const QString &name, const QString &publicId, const QString &systemId)

Reimplements: QXmlDeclHandler::externalEntityDecl(const QString &name, const QString &publicId, const QString &systemId).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::fatalError(const QXmlParseException &exception)

Reimplements: QXmlErrorHandler::fatalError(const QXmlParseException &exception).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::ignorableWhitespace(const QString &ch)

Reimplements: QXmlContentHandler::ignorableWhitespace(const QString &ch).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::internalEntityDecl(const QString &name, const QString &value)

Reimplements: QXmlDeclHandler::internalEntityDecl(const QString &name, const QString &value).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::notationDecl(const QString &name, const QString &publicId, const QString &systemId)

Reimplements: QXmlDTDHandler::notationDecl(const QString &name, const QString &publicId, const QString &systemId).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::processingInstruction(const QString &target, const QString &data)

Reimplements: QXmlContentHandler::processingInstruction(const QString &target, const QString &data).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::resolveEntity(const QString &publicId, const QString &systemId, QXmlInputSource *&ret)

Reimplements: QXmlEntityResolver::resolveEntity(const QString &publicId, const QString &systemId, QXmlInputSource *&ret).

Sets ret to `nullptr`, so that the reader uses the system identifier provided in the XML document.

### `[override virtual]` void QXmlDefaultHandler::setDocumentLocator(QXmlLocator *locator)

Reimplements: QXmlContentHandler::setDocumentLocator(QXmlLocator *locator).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::skippedEntity(const QString &name)

Reimplements: QXmlContentHandler::skippedEntity(const QString &name).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::startCDATA()

Reimplements: QXmlLexicalHandler::startCDATA().

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::startDTD(const QString &name, const QString &publicId, const QString &systemId)

Reimplements: QXmlLexicalHandler::startDTD(const QString &name, const QString &publicId, const QString &systemId).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::startDocument()

Reimplements: QXmlContentHandler::startDocument().

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::startElement(const QString &namespaceURI, const QString &localName, const QString &qName, const QXmlAttributes &atts)

Reimplements: QXmlContentHandler::startElement(const QString &namespaceURI, const QString &localName, const QString &qName, const QXmlAttributes &atts).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::startEntity(const QString &name)

Reimplements: QXmlLexicalHandler::startEntity(const QString &name).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::startPrefixMapping(const QString &prefix, const QString &uri)

Reimplements: QXmlContentHandler::startPrefixMapping(const QString &prefix, const QString &uri).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::unparsedEntityDecl(const QString &name, const QString &publicId, const QString &systemId, const QString &notationName)

Reimplements: QXmlDTDHandler::unparsedEntityDecl(const QString &name, const QString &publicId, const QString &systemId, const QString &notationName).

This reimplementation does nothing.

### `[override virtual]` bool QXmlDefaultHandler::warning(const QXmlParseException &exception)

Reimplements: QXmlErrorHandler::warning(const QXmlParseException &exception).

This reimplementation does nothing.