QgsPropertyCollection class

A grouped map of multiple QgsProperty objects, each referenced by a integer key value.

Reference

Properties within a collection are referenced by an integer key. This is done to avoid the cost of string creation and comparisons which would be required by a string key. The intended use case is that a context specific enum is cast to int and used for the key value.

Base classes

class QgsAbstractPropertyCollection: Abstract base class for QgsPropertyCollection like objects.

Constructors, destructors, conversion operators

QgsPropertyCollection(const QString& name = QString()): Constructor for QgsPropertyCollection.
QgsPropertyCollection(const QgsPropertyCollection& other): Copy constructor.

Public functions

void clear() override: Removes all properties from the collection.
auto count() const -> int: Returns the number of properties contained within the collection.
auto hasActiveProperties() const -> bool override: Returns true if the collection has any active properties, or false if all properties within the collection are deactivated.
auto hasDynamicProperties() const -> bool override: Returns true if the collection has any active, non-static properties, or false if either all non-static properties within the collection are deactivated or if the collection only contains static properties.
auto hasProperty(int key) const -> bool override: Returns true if the collection contains a property with the specified key.
auto isActive(int key) const -> bool override: Returns true if the collection contains an active property with the specified key.
auto loadVariant(const QVariant& configuration, const QgsPropertiesDefinition& definitions) -> bool override: Loads this property collection from a QVariantMap, wrapped in a QVariant.
auto prepare(const QgsExpressionContext& context = QgsExpressionContext()) const -> bool override: Prepares the collection against a specified expression context.
auto property(int key) const -> QgsProperty override: Returns a matching property from the collection, if one exists.
auto property(int key) -> QgsProperty& virtual: Returns a reference to a matching property from the collection, if one exists.
auto propertyKeys() const -> QSet<int> override: Returns a list of property keys contained within the collection.
auto referencedFields(const QgsExpressionContext& context = QgsExpressionContext()) const -> QSet<QString> override: Returns the set of any fields referenced by the active properties from the collection.
void setProperty(int key, const QgsProperty& property): Adds a property to the collection and takes ownership of it.
void setProperty(int key, const QVariant& value): Convenience method, creates a QgsStaticProperty and stores it within the collection.
auto toVariant(const QgsPropertiesDefinition& definitions) const -> QVariant override: Saves this property collection to a QVariantMap, wrapped in a QVariant.
auto value(int key, const QgsExpressionContext& context, const QVariant& defaultValue = QVariant()) const -> QVariant override: Returns the calculated value of the property with the specified key from within the collection.

Function documentation

QgsPropertyCollection::QgsPropertyCollection(const QString& name = QString())

Constructor for QgsPropertyCollection.

Parameters
name	collection name

bool QgsPropertyCollection::hasActiveProperties() const override

Returns true if the collection has any active properties, or false if all properties within the collection are deactivated.

bool QgsPropertyCollection::hasDynamicProperties() const override

Returns true if the collection has any active, non-static properties, or false if either all non-static properties within the collection are deactivated or if the collection only contains static properties.

bool QgsPropertyCollection::hasProperty(int key) const override

Returns true if the collection contains a property with the specified key.

Parameters
key	integer key for property. The intended use case is that a context specific enum is cast to int and used for the key value.

bool QgsPropertyCollection::isActive(int key) const override

Returns true if the collection contains an active property with the specified key.

Parameters
key	integer key for property to test. The intended use case is that a context specific enum is cast to int and used for the key value.

bool QgsPropertyCollection::loadVariant(const QVariant& configuration, const QgsPropertiesDefinition& definitions) override

Loads this property collection from a QVariantMap, wrapped in a QVariant.

You can use QgsXmlUtils::readVariant to save it to an XML document.

bool QgsPropertyCollection::prepare(const QgsExpressionContext& context = QgsExpressionContext()) const override

Prepares the collection against a specified expression context.

Calling prepare before evaluating the collection's properties multiple times allows precalculation of expensive setup tasks such as parsing expressions. Returns true if preparation was successful.

QgsProperty QgsPropertyCollection::property(int key) const override

Returns a matching property from the collection, if one exists.

Parameters
key	integer key for property to return. The intended use case is that a context specific enum is cast to int and used for the key value.
Returns	matching property, or null if no matching, active property found.

QgsProperty& QgsPropertyCollection::property(int key) virtual

Returns a reference to a matching property from the collection, if one exists.

Parameters
key	integer key for property to return. The intended use case is that a context specific enum is cast to int and used for the key value.
Returns	matching property, or null if no matching, active property found.

QSet<QString> QgsPropertyCollection::referencedFields(const QgsExpressionContext& context = QgsExpressionContext()) const override

Returns the set of any fields referenced by the active properties from the collection.

Parameters
context	expression context the properties will be evaluated against.

void QgsPropertyCollection::setProperty(int key, const QgsProperty& property)

Adds a property to the collection and takes ownership of it.

Parameters
key	integer key for property. Any existing property with the same key will be removed and replaced by this property. The intended use case is that a context specific enum is cast to int and used for the key value.
property	property to add. Ownership is transferred to the collection. Setting an invalid property will remove the property from the collection.

void QgsPropertyCollection::setProperty(int key, const QVariant& value)

Convenience method, creates a QgsStaticProperty and stores it within the collection.

Parameters
key	integer key for property. Any existing property with the same key will be deleted and replaced by this property. The intended use case is that a context specific enum is cast to int and used for the key value.
value	static value for property

QVariant QgsPropertyCollection::toVariant(const QgsPropertiesDefinition& definitions) const override

Saves this property collection to a QVariantMap, wrapped in a QVariant.

You can use QgsXmlUtils::writeVariant to save it to an XML document.

QVariant QgsPropertyCollection::value(int key, const QgsExpressionContext& context, const QVariant& defaultValue = QVariant()) const override

Returns the calculated value of the property with the specified key from within the collection.

Parameters
key	integer key for property to return. The intended use case is that a context specific enum is cast to int and used for the key value.
context	expression context to evaluate property against
defaultValue	default value to return if no matching, active property found or if the property value cannot be calculated
Returns	calculated property value, or default value if property could not be evaluated