The QScxmlCppDataModel class is a C++ data model for a Qt SCXML state machine. More...
| Header: | #include <QScxmlCppDataModel> |
| qmake: | QT += scxml |
| Since: | Qt 5.7 |
| Inherits: | QScxmlDataModel |
| QScxmlCppDataModel(QObject *parent = nullptr) | |
| bool | inState(const QString &stateName) const |
| const QScxmlEvent & | scxmlEvent() const |
| virtual void | evaluateAssignment(QScxmlExecutableContent::EvaluatorId id, bool *ok) override |
| virtual void | evaluateForeach(QScxmlExecutableContent::EvaluatorId id, bool *ok, QScxmlDataModel::ForeachLoopBody *body) override |
| virtual void | evaluateInitialization(QScxmlExecutableContent::EvaluatorId id, bool *ok) override |
| virtual bool | hasScxmlProperty(const QString &name) const override |
| virtual QVariant | scxmlProperty(const QString &name) const override |
| virtual void | setScxmlEvent(const QScxmlEvent &event) override |
| virtual bool | setScxmlProperty(const QString &name, const QVariant &value, const QString &context) override |
| virtual bool | setup(const QVariantMap &initialDataValues) override |
The QScxmlCppDataModel class is a C++ data model for a Qt SCXML state machine.
The C++ data model for SCXML lets you write C++ code for expr attributes and <script> elements. The data part of the data model is backed by a subclass of QScxmlCppDataModel, for which the Qt SCXML compiler (qscxmlc) will generate the dispatch methods. It cannot be used when loading an SCXML file at runtime.
Usage is through the datamodel attribute of the <scxml> element:
<scxml datamodel="cplusplus:TheDataModel:thedatamodel.h" ....>
The format of the datamodel attribute is: cplusplus:<class-name>:<classdef-header>. So, for the example above, there should be a file thedatamodel.h containing a subclass of QScxmlCppDataModel, containing at least the following:
#include "qscxmlcppdatamodel.h" class TheDataModel: public QScxmlCppDataModel { Q_OBJECT Q_SCXML_DATAMODEL };
The Q_SCXML_DATAMODEL has to appear in the private section of the class definition, for example right after the opening bracket, or after a Q_OBJECT macro. This macro expands to the declaration of some virtual methods whose implementation is generated by the Qt SCXML compiler.
The Qt SCXML compiler will generate the various evaluateTo methods, and convert expressions and scripts into lambdas inside those methods. For example:
<scxml datamodel="cplusplus:TheDataModel:thedatamodel.h" xmlns="http://www.w3.org/2005/07/scxml" version="1.0" name="MediaPlayerStateMachine"> <state id="stopped"> <transition event="tap" cond="isValidMedia()" target="playing"/> </state> <state id="playing"> <onentry> <script> media = eventData().value(QStringLiteral("media")).toString(); </script> <send event="playbackStarted"> <param name="media" expr="media"/> </send> </onentry> </state> </scxml>
This will result in:
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(); }(); // .... }
So, you are not limited to call functions. In a <script> element you can put zero or more C++ statements, and in cond or expr attributes you can use any C++ expression that can be converted
to the respective bool or QVariant. And, as the this pointer is also captured, you can call or access the data model (the media attribute in the example above). For the full
example, see Qt SCXML: Media Player QML Example (C++ Data Model).
See also QScxmlStateMachine and QScxmlDataModel.
Creates a new C++ data model with the parent object parent.
[override virtual] void QScxmlCppDataModel::evaluateAssignment(QScxmlExecutableContent::EvaluatorId id, bool *ok)Reimplemented from QScxmlDataModel::evaluateAssignment().
This method does not perform any action, ignores id, and sets ok to false. Override it in your specific data model in order to implement <assign>.
[override virtual] void QScxmlCppDataModel::evaluateForeach(QScxmlExecutableContent::EvaluatorId id, bool *ok, QScxmlDataModel::ForeachLoopBody
*body)Reimplemented from QScxmlDataModel::evaluateForeach().
This method does not perform any action, ignores id and body, and sets ok to false. Override it in your specific data model in order to implement <foreach>.
[override virtual] void QScxmlCppDataModel::evaluateInitialization(QScxmlExecutableContent::EvaluatorId id, bool *ok)Reimplemented from QScxmlDataModel::evaluateInitialization().
This method does not perform any action, ignores id, and sets ok to false. Override it in your specific data model in order to implement <data>.
[override virtual] bool QScxmlCppDataModel::hasScxmlProperty(const
QString &name) constReimplemented from QScxmlDataModel::hasScxmlProperty().
This method always returns false and ignores name. Override it to implement the lookup of data model properties via the location attribute of various elements.
Returns true if the state machine is in the state specified by stateName, false otherwise.
Holds the current event that is being processed by the state machine.
See also SCXML Specification - 5.10 System Variables for the description of the _event variable.
Returns the event currently being processed.
See also setScxmlEvent().
[override virtual] QVariant QScxmlCppDataModel::scxmlProperty(const QString &name) constReimplemented from QScxmlDataModel::scxmlProperty().
This method always returns an empty QVariant and ignores name. Override it to implement the lookup of data model properties via the location attribute of various
elements.
See also setScxmlProperty().
[override virtual] void QScxmlCppDataModel::setScxmlEvent(const QScxmlEvent &event)Reimplemented from QScxmlDataModel::setScxmlEvent().
Sets the event that will be processed next.
See also QScxmlCppDataModel::scxmlEvent.
[override virtual] bool QScxmlCppDataModel::setScxmlProperty(const
QString &name, const QVariant &value, const QString &context)Reimplemented from QScxmlDataModel::setScxmlProperty().
This method always returns false and ignores name, value, and context. Override it to implement the lookup of data model properties via the location attribute of various
elements.
See also scxmlProperty().
[override virtual] bool QScxmlCppDataModel::setup(const QVariantMap &initialDataValues)Reimplemented from QScxmlDataModel::setup().
Called during state machine initialization to set up a state machine using the initial values for data model variables specified by their keys, initialDataValues. These are the values specified by
<param> tags in an <invoke> element.
Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.
See also QScxmlStateMachine::init.
