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++ // Copyright (C) 2023 The Qt Company Ltd.
++ // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
++
++ /*!
++ \example mediaplayer
++ \title SCXML Media Player
++ \examplecategory {Data Processing & I/O}
++ \ingroup examples-qtscxml
++ \meta tag {state machine}
++
++ \image mediaplayer.png
++ {Media player with song list on left and Stopped status on right}
++
++ \brief Sends data to and receives it from a C++ data model.
++
++ \e {Media Player} demonstrates how to access
++ data from a C++ data model. The data model enables writing C++ code for
++ \e expr attributes and \c <script> elements. The \e {data part} of the data
++ model is backed by a subclass of QScxmlCppDataModel, for which the Qt SCXML
++ compiler (\c qscxmlc) generates the dispatch methods.
++
++ The UI is created using Qt Quick.
++
++ \include examples-run.qdocinc
++
++ \section1 Using the C++ Data Model
++
++ We specify the data model as a value of the \e datamodel attribute of the
++ \c <scxml> element in the SCXML file:
++
++ \quotefromfile mediaplayer/mediaplayer.scxml
++ \skipto scxml
++ \printuntil datamodel
++
++ The format of the \e datamodel attribute is:
++ \c {cplusplus:<class-name>:<classdef-header>}. Therefore, we need a file
++ called \e thedatamodel.h that contains a subclass of QScxmlCppDataModel:
++
++ \quotefromfile mediaplayer/thedatamodel.h
++ \skipto qscxmlcppdatamodel.h
++ \printuntil Q_SCXML_DATAMODEL
++
++ QScxmlCppDataModel derives from QObject, so we add the \c Q_OBJECT macro in
++ the private section of the definition, right after the opening bracket. We
++ then place the \c Q_SCXML_DATAMODEL macro after \c Q_OBJECT. The macro
++ expands to the declaration of virtual methods, the implementation of which
++ is generated by the Qt SCXML compiler.
++
++ In the SCXML file, we specify C++ statements in the \c <script> element and
++ use the \e expr attribute to access the data model:
++
++ \quotefromfile mediaplayer/mediaplayer.scxml
++ \skipto state
++ \printuntil </state>
++ \printuntil </state>
++
++ The Qt SCXML compiler generates the various \c evaluateTo methods and
++ converts the expressions and scripts into lambdas inside those methods in
++ \e mediaplayer.cpp:
++
++ \code
++ bool TheDataModel::evaluateToBool(QScxmlExecutableContent::EvaluatorId id, bool *ok) {
++ ....
++ return [this]()->bool{ return isValidMedia(); }();
++ ....
++ }
++
++ QVariant TheDataModel::evaluateToVariant(QScxmlExecutableContent::EvaluatorId id, bool *ok) {
++ ....
++ return [this]()->QVariant{ return media; }();
++ ....
++ }
++
++ void TheDataModel::evaluateToVoid(QScxmlExecutableContent::EvaluatorId id, bool *ok) {
++ ....
++ [this]()->void{ media = eventData().value(QStringLiteral("media")).toString(); }();
++ ....
++ }
++ \endcode
++ */