- Qt 6.6
- Qt SCXML
- C++ Classes
- QScxmlNullDataModel
- Qt 6.6.0 Reference Documentation

# QScxmlNullDataModel Class

The QScxmlNullDataModel class is the null data model for a Qt SCXML stateMachine. More...

Header: | #include <QScxmlNullDataModel>
CMake: | find_package(Qt6 REQUIRED COMPONENTS Scxml) target_link_libraries(mytarget PRIVATE Qt6::Scxml)
qmake: | QT += scxml
Inherits: | QScxmlDataModel

- List of all members, including inherited members

## Public Functions

| QScxmlNullDataModel(QObject *parent = nullptr)
virtual | ~QScxmlNullDataModel()

## Reimplemented Public Functions

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 | evaluateToBool(QScxmlExecutableContent::EvaluatorId id, bool *ok) override
virtual QString | evaluateToString(QScxmlExecutableContent::EvaluatorId id, bool *ok) override
virtual QVariant | evaluateToVariant(QScxmlExecutableContent::EvaluatorId id, bool *ok) override
virtual void | evaluateToVoid(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

## Detailed Description

This class implements the null data model as described in the SCXML Specification - B.1 The Null Data Model. Using the value `"null"` for the datamodel attribute of the `<scxml>` element means that there is no underlying data model, but some executable content, like `In(...)` or `<log>` can still be used.

See also QScxmlStateMachine and QScxmlDataModel.

## Member Function Documentation

### `[explicit]` QScxmlNullDataModel::QScxmlNullDataModel(QObject *parent = nullptr)

Creates a new Qt SCXML null data model, with the parent object parent.

### `[virtual noexcept]` QScxmlNullDataModel::~QScxmlNullDataModel()

Destroys the data model.

### `[override virtual]` void QScxmlNullDataModel::evaluateAssignment(QScxmlExecutableContent::EvaluatorId id, bool *ok)

Reimplements: QScxmlDataModel::evaluateAssignment(QScxmlExecutableContent::EvaluatorId id, bool *ok).

Throws an error and sets ok to `false`, because the null data model cannot evaluate assignments.

### `[override virtual]` void QScxmlNullDataModel::evaluateForeach(QScxmlExecutableContent::EvaluatorId id, bool *ok, QScxmlDataModel::ForeachLoopBody *body)

Reimplements: QScxmlDataModel::evaluateForeach(QScxmlExecutableContent::EvaluatorId id, bool *ok, QScxmlDataModel::ForeachLoopBody *body).

Throws an error and sets ok to `false`, because the null data model cannot evaluate `<foreach>` blocks.

### `[override virtual]` void QScxmlNullDataModel::evaluateInitialization(QScxmlExecutableContent::EvaluatorId id, bool *ok)

Reimplements: QScxmlDataModel::evaluateInitialization(QScxmlExecutableContent::EvaluatorId id, bool *ok).

Throws an error and sets ok to `false`, because the null data model cannot initialize data.

### `[override virtual]` bool QScxmlNullDataModel::evaluateToBool(QScxmlExecutableContent::EvaluatorId id, bool *ok)

Reimplements: QScxmlDataModel::evaluateToBool(QScxmlExecutableContent::EvaluatorId id, bool *ok).

Evaluates the executable content pointed to by id and records in ok whether there was an error. Returns the result of the evaluation as a boolean value. The null data model can evaluate the instruction `In(...)`, so this might result in an actual value, rather than an error.

### `[override virtual]` QString QScxmlNullDataModel::evaluateToString(QScxmlExecutableContent::EvaluatorId id, bool *ok)

Reimplements: QScxmlDataModel::evaluateToString(QScxmlExecutableContent::EvaluatorId id, bool *ok).

Evaluates the executable content pointed to by id and records in ok whether there was an error. Returns the result of the evaluation as a string. The null data model can evaluate the `<log>` element, so this might result in an actual value, rather than an error

### `[override virtual]` QVariant QScxmlNullDataModel::evaluateToVariant(QScxmlExecutableContent::EvaluatorId id, bool *ok)

Reimplements: QScxmlDataModel::evaluateToVariant(QScxmlExecutableContent::EvaluatorId id, bool *ok).

Evaluates the executable content pointed to by id and records in ok whether there was an error. As this is the null data model, any evaluation will in fact result in an error, with ok set to `false`. Returns an empty QVariant.

### `[override virtual]` void QScxmlNullDataModel::evaluateToVoid(QScxmlExecutableContent::EvaluatorId id, bool *ok)

Reimplements: QScxmlDataModel::evaluateToVoid(QScxmlExecutableContent::EvaluatorId id, bool *ok).

Evaluates the executable content pointed to by id and records in ok whether there was an error. As this is the null data model, any evaluation will in fact result in an error, with ok set to `false`.

### `[override virtual]` bool QScxmlNullDataModel::hasScxmlProperty(const QString &name) const

Reimplements: QScxmlDataModel::hasScxmlProperty(const QString &name) const.

Returns `false`, because the null data model does not support properties.

### `[override virtual]` QVariant QScxmlNullDataModel::scxmlProperty(const QString &name) const

Reimplements: QScxmlDataModel::scxmlProperty(const QString &name) const.

Returns an invalid variant, because the null data model does not support properties.

See also setScxmlProperty().

### `[override virtual]` void QScxmlNullDataModel::setScxmlEvent(const QScxmlEvent &event)

Reimplements: QScxmlDataModel::setScxmlEvent(const QScxmlEvent &event).

Does not actually set the event, because the null data model does not handle events.

### `[override virtual]` bool QScxmlNullDataModel::setScxmlProperty(const QString &name, const QVariant &value, const QString &context)

Reimplements: QScxmlDataModel::setScxmlProperty(const QString &name, const QVariant &value, const QString &context).

Returns `false`, because the null data model does not support properties.

See also scxmlProperty().

### `[override virtual invokable]` bool QScxmlNullDataModel::setup(const QVariantMap &initialDataValues)

Reimplements: QScxmlDataModel::setup(const QVariantMap &initialDataValues).