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Please review the following information to ensure ** the GNU Free Documentation License version 1.3 requirements ** will be met: https://www.gnu.org/licenses/fdl-1.3.html. ** $QT_END_LICENSE$ ** ****************************************************************************/ /*! \group xml-tools \title XML Classes \brief Classes that support XML. These classes are relevant to XML users. \generatelist{related} */ /*! \page xml-processing.html \title XML Processing \brief An Overview of the XML processing facilities in Qt. Qt provides two general-purpose sets of APIs to read and write well-formed XML: \l{XML Streaming}{stream based} and \l{Working with the DOM Tree}{DOM based}. Qt also provides specific support for some XML dialects. For instance, the Qt SVG module provides the QSvgRenderer and QSvgGenerator classes to read and write a subset of SVG, an XML-based file format. Qt also provides helper functions that may be useful to those working with XML and XHTML: see Qt::escape() and Qt::convertFromPlainText(). \section1 Topics: \list \li \l {Classes for XML Processing} \li \l {An Introduction to Namespaces} \li \l {XML Streaming} \li \l {Working with the DOM Tree} \endlist \section1 Classes for XML Processing These classes are relevant to XML users. \annotatedlist xml-tools */ /*! \page xml-namespaces.html \title An Introduction to Namespaces \target namespaces \nextpage XML Streaming Parts of the Qt XML module documentation assume that you are familiar with XML namespaces. Here we present a brief introduction; skip to \l{#namespacesConventions}{Qt XML documentation conventions} if you already know this material. Namespaces are a concept introduced into XML to allow a more modular design. With their help data processing software can easily resolve naming conflicts in XML documents. Consider the following example: \snippet code/doc_src_qtxml.qdoc 6 Here we find three different uses of the name \e title. If you wish to process this document you will encounter problems because each of the \e titles should be displayed in a different manner -- even though they have the same name. The solution would be to have some means of identifying the first occurrence of \e title as the title of a book, i.e. to use the \e title element of a book namespace to distinguish it from, for example, the chapter title, e.g.: \snippet code/doc_src_qtxml.qdoc 7 \e book in this case is a \e prefix denoting the namespace. Before we can apply a namespace to element or attribute names we must declare it. Namespaces are URIs like \e http://www.example.com/fnord/book/. This does not mean that data must be available at this address; the URI is simply used to provide a unique name. We declare namespaces in the same way as attributes; strictly speaking they \e are attributes. To make for example \e http://www.example.com/fnord/ the document's default XML namespace \e xmlns we write \snippet code/doc_src_qtxml.qdoc 8 To distinguish the \e http://www.example.com/fnord/book/ namespace from the default, we must supply it with a prefix: \snippet code/doc_src_qtxml.qdoc 9 A namespace that is declared like this can be applied to element and attribute names by prepending the appropriate prefix and a ":" delimiter. We have already seen this with the \e book:title element. Element names without a prefix belong to the default namespace. This rule does not apply to attributes: an attribute without a prefix does not belong to any of the declared XML namespaces at all. Attributes always belong to the "traditional" namespace of the element in which they appear. A "traditional" namespace is not an XML namespace, it simply means that all attribute names belonging to one element must be different. Later we will see how to assign an XML namespace to an attribute. Due to the fact that attributes without prefixes are not in any XML namespace there is no collision between the attribute \e title (that belongs to the \e author element) and for example the \e title element within a \e chapter. Let's clarify this with an example: \snippet code/doc_src_qtxml.qdoc 10 Within the \e document element we have two namespaces declared. The default namespace \e http://www.example.com/fnord/ applies to the \e book element, the \e chapter element, the appropriate \e title element and of course to \e document itself. The \e book:author and \e book:title elements belong to the namespace with the URI \e http://www.example.com/fnord/book/. The two \e book:author attributes \e title and \e name have no XML namespace assigned. They are only members of the "traditional" namespace of the element \e book:author, meaning that for example two \e title attributes in \e book:author are forbidden. In the above example we circumvent the last rule by adding a \e title attribute from the \e http://www.example.com/fnord/ namespace to \e book:author: the \e fnord:title comes from the namespace with the prefix \e fnord that is declared in the \e book:author element. Clearly the \e fnord namespace has the same namespace URI as the default namespace. So why didn't we simply use the default namespace we'd already declared? The answer is quite complex: \list \li attributes without a prefix don't belong to any XML namespace at all, not even to the default namespace; \li additionally omitting the prefix would lead to a \e title-title clash; \li writing it as \e xmlns:title would declare a new namespace with the prefix \e title instead of applying the default \e xmlns namespace. \endlist With the Qt XML classes elements and attributes can be accessed in two ways: either by referring to their qualified names consisting of the namespace prefix and the "real" name (or \e local name) or by the combination of local name and namespace URI. More information on XML namespaces can be found at \l http://www.w3.org/TR/REC-xml-names/. \target namespacesConventions \section1 Conventions Used in the Qt XML Documentation The following terms are used to distinguish the parts of names within the context of namespaces: \list \li The \e {qualified name} is the name as it appears in the document. (In the above example \e book:title is a qualified name.) \li A \e {namespace prefix} in a qualified name is the part to the left of the ":". (\e book is the namespace prefix in \e book:title.) \li The \e {local part} of a name (also referred to as the \e {local name}) appears to the right of the ":". (Thus \e title is the local part of \e book:title.) \li The \e {namespace URI} ("Uniform Resource Identifier") is a unique identifier for a namespace. It looks like a URL (e.g. \e http://www.example.com/fnord/ ) but does not require data to be accessible by the given protocol at the named address. \endlist Elements without a ":" (like \e chapter in the example) do not have a namespace prefix. In this case the local part and the qualified name are identical (i.e. \e chapter). \sa {DOM Bookmarks Example} */ /*! \page xml-streaming.html \title XML Streaming \previouspage An Introduction to Namespaces \nextpage Working with the DOM Tree Qt provides two classes for reading and writing XML through a simple streaming API: QXmlStreamReader and QXmlStreamWriter. A stream reader reports an XML document as a stream of tokens. This differs from SAX as SAX applications provide handlers to receive XML events from the parser whereas the QXmlStreamReader drives the loop, pulling tokens from the reader when they are needed. This pulling approach makes it possible to build recursive descent parsers, allowing XML parsing code to be split into different methods or classes. QXmlStreamReader is a well-formed XML 1.0 parser that excludes external parsed entities. Hence, data provided by the stream reader adheres to the W3C's criteria for well-formed XML, as long as no error occurs. Otherwise, functions such as \l{QXmlStreamReader::atEnd()}{atEnd()}, \l{QXmlStreamReader::error()}{error()} and \l{QXmlStreamReader::hasError()} {hasError()} can be used to check and view the errors. An example of QXmlStreamReader implementation would be the \c XbelReader in \l{QXmlStream Bookmarks Example}, which wraps a QXmlStreamReader. The constructor takes \a treeWidget as a parameter and the class has Xbel specific functions: \snippet streambookmarks/xbelreader.h 1 \dots \snippet streambookmarks/xbelreader.h 2 \dots The \c read() function accepts a QIODevice and sets it with \l{QXmlStreamReader::setDevice()}{setDevice()}. The \l{QXmlStreamReader::raiseError()}{raiseError()} function is used to display a custom error message, inidicating that the file's version is incorrect. \snippet streambookmarks/xbelreader.cpp 1 The pendent to QXmlStreamReader is QXmlStreamWriter, which provides an XML writer with a simple streaming API. QXmlStreamWriter operates on a QIODevice and has specialized functions for all XML tokens or events you want to write, such as \l{QXmlStreamWriter::writeDTD()}{writeDTD()}, \l{QXmlStreamWriter::writeCharacters()}{writeCharacters()}, \l{QXmlStreamWriter::writeComment()}{writeComment()} and so on. To write XML document with QXmlStreamWriter, you start a document with the \l{QXmlStreamWriter::writeStartDocument()}{writeStartDocument()} function and end it with \l{QXmlStreamWriter::writeEndDocument()} {writeEndDocument()}, which implicitly closes all remaining open tags. Element tags are opened with \l{QXmlStreamWriter::writeStartDocument()} {writeStartDocument()} and followed by \l{QXmlStreamWriter::writeAttribute()}{writeAttribute()} or \l{QXmlStreamWriter::writeAttributes()}{writeAttributes()}, element content, and then \l{QXmlStreamWriter::writeEndDocument()} {writeEndDocument()}. Also, \l{QXmlStreamWriter::writeEmptyElement()} {writeEmptyElement()} can be used to write empty elements. Element content comprises characters, entity references or nested elements. Content can be written with \l{QXmlStreamWriter::writeCharacters()} {writeCharacters()}, a function that also takes care of escaping all forbidden characters and character sequences, \l{QXmlStreamWriter::writeEntityReference()}{writeEntityReference()}, or subsequent calls to \l{QXmlStreamWriter::writeStartElement()} {writeStartElement()}. The \c XbelWriter class from \l{QXmlStream Bookmarks Example} wraps a QXmlStreamWriter. Its \c writeFile() function illustrates the core functions of QXmlStreamWriter mentioned above: \snippet streambookmarks/xbelwriter.cpp 1 */ /*! \page xml-dom.tml \title Working with the DOM Tree \target dom \previouspage XML Streaming DOM Level 2 is a W3C Recommendation for XML interfaces that maps the constituents of an XML document to a tree structure. The specification of DOM Level 2 can be found at \l{http://www.w3.org/DOM/}. \target domIntro \section1 Introduction to DOM DOM provides an interface to access and change the content and structure of an XML file. It makes a hierarchical view of the document (a tree view). Thus -- in contrast to the streaming API provided by QXmlStreamReader -- an object model of the document is resident in memory after parsing which makes manipulation easy. All DOM nodes in the document tree are subclasses of \l QDomNode. The document itself is represented as a \l QDomDocument object. Here are the available node classes and their potential child classes: \list \li \l QDomDocument: Possible children are \list \li \l QDomElement (at most one) \li \l QDomProcessingInstruction \li \l QDomComment \li \l QDomDocumentType \endlist \li \l QDomDocumentFragment: Possible children are \list \li \l QDomElement \li \l QDomProcessingInstruction \li \l QDomComment \li \l QDomText \li \l QDomCDATASection \li \l QDomEntityReference \endlist \li \l QDomDocumentType: No children \li \l QDomEntityReference: Possible children are \list \li \l QDomElement \li \l QDomProcessingInstruction \li \l QDomComment \li \l QDomText \li \l QDomCDATASection \li \l QDomEntityReference \endlist \li \l QDomElement: Possible children are \list \li \l QDomElement \li \l QDomText \li \l QDomComment \li \l QDomProcessingInstruction \li \l QDomCDATASection \li \l QDomEntityReference \endlist \li \l QDomAttr: Possible children are \list \li \l QDomText \li \l QDomEntityReference \endlist \li \l QDomProcessingInstruction: No children \li \l QDomComment: No children \li \l QDomText: No children \li \l QDomCDATASection: No children \li \l QDomEntity: Possible children are \list \li \l QDomElement \li \l QDomProcessingInstruction \li \l QDomComment \li \l QDomText \li \l QDomCDATASection \li \l QDomEntityReference \endlist \li \l QDomNotation: No children \endlist With \l QDomNodeList and \l QDomNamedNodeMap two collection classes are provided: \l QDomNodeList is a list of nodes, and \l QDomNamedNodeMap is used to handle unordered sets of nodes (often used for attributes). The \l QDomImplementation class allows the user to query features of the DOM implementation. To get started please refer to the \l QDomDocument documentation. You might also want to take a look at the \l{DOM Bookmarks Example}, which illustrates how to read and write an XML bookmark file (XBEL) using DOM. */