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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
*/