qt6-changes.qdoc

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// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
    \page xml-changes-qt6.html
    \title Changes to Qt XML
    \ingroup changes-qt-5-to-6
    \brief Use QXmlStreamReader for reading XML files.
 
    Qt 6 is a result of the conscious effort to make the framework more
    efficient and easy to use.
 
    We try to maintain binary and source compatibility for all the public
    APIs in each release. But some changes were inevitable in an effort to
    make Qt a better framework.
 
    In this topic we summarize those changes in Qt XML, and provide
    guidance to handle them.
 
    \section1 Simple API for XML (SAX) parser
    All \b SAX classes have been removed from Qt XML. Use
    QXmlStreamReader for reading XML files. Here are some simple steps to
    port your current code to QXmlStreamReader:
 
    For example, if you have code like
 
    \code
        QFile *file = new QFile(...);
        QXmlInputSource *source = new QXmlInputSource(file);
 
        Handler *handler = new Handler;
 
        QXmlSimpleReader xmlReader;
        xmlReader.setErrorHandler(handler);
        xmlReader.setContentHandler(handler);
 
        if (xmlReader.parse(source)) {
            ... // do processing
        } else {
            ... // do error handling
        }
    \endcode
 
    you can rewrite it as
 
    \code
        QFile file = ...;
        QXmlStreamReader reader(&file);
 
        while (!reader.atEnd()) {
            reader.readNext();
            ... // do processing
        }
        if (reader.hasError()) {
            ... // do error handling
        }
    \endcode
 
    \section2 QDom and QDomDocument
 
    As \b SAX classes have been removed from Qt XML, QDomDocument
    has been re-implemented using QXmlStreamReader.
    This causes a few behavioral changes:
 
    \list
        \li Attribute values will be normalized. For example,
        \c{<tag attr=" a \n b " />} is equivalent to \c{<tag attr="a b"/>}.
        \li Identical qualified attribute names are no longer allowed. This
        means attributes of an element must have unique names.
        \li Undeclared namespace prefixes are no longer allowed.
    \endlist
 
    If you use QDomDocument and rely on any of these, you must update
    your code and XML documents accordingly.
 
    \section3 Spacing-only text nodes
 
    By default, text nodes containing only spacing characters are stripped
    and won't appear in the QDomDocument. The Qt 5 way of changing this behavior
    was using the QDomDocument::setContent() overload that allowed a \c QXmlReader
    to be supplied. That overload was removed in Qt 6.0, but since Qt 6.5,
    you can pass QDomDocument::ParseOption::PreserveSpacingOnlyNodes as a parse
    option, to specify that spacing-only text nodes must be preserved.
 
    \section2 Qt Core5 compatibility library
 
    If your application or library cannot be ported right now, the \l
    QXmlSimpleReader and related classes still exist in Qt5Compat to keep
    old code-bases working. If you want to use those SAX classes further, you
    need to link against the new Qt5Compat module and add this line to your \l
    qmake \c .pro file:
 
    \code
        QT += core5compat
    \endcode
 
    In case you already ported your application or library to the
    \l {Build with CMake}{cmake} build system, add the following to your
    \c CMakeList.txt:
    \code
        PUBLIC_LIBRARIES
            Qt::Core5Compat
    \endcode
*/