Class: QgsAbstractPropertyCollection

Abstract base class for QgsPropertyCollection like objects.

Note

This is an abstract class, with methods which must be implemented by a subclass.

The following methods must be implemented: clear(), hasActiveProperties(), hasDynamicProperties(), hasProperty(), isActive(), loadVariant(), prepare(), property(), propertyKeys(), referencedFields(), toVariant(), value()

Class Hierarchy

Subclasses

QgsPropertyCollection	A grouped map of multiple QgsProperty objects, each referenced by an integer key value.
QgsPropertyCollectionStack	An ordered stack of QgsPropertyCollection containers, where collections added later to the stack will take priority over earlier collections.

Abstract Methods

clear	Removes all properties from the collection.
hasActiveProperties	Returns True if the collection has any active properties, or False if all properties within the collection are deactivated.
hasDynamicProperties	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.
hasProperty	Returns True if the collection contains a property with the specified key.
isActive	Returns True if the collection contains an active property with the specified key.
loadVariant	Loads this property collection from a QVariantMap, wrapped in a QVariant.
prepare	Prepares the collection against a specified expression context.
property	Returns a matching property from the collection, if one exists.
propertyKeys	Returns a list of property keys contained within the collection.
referencedFields	Returns the set of any fields referenced by the active properties from the collection.
toVariant	Saves this property collection to a QVariantMap, wrapped in a QVariant.
value	Returns the calculated value of the property with the specified key from within the collection.

Methods

name	Returns the descriptive name of the property collection.
setName	Sets the descriptive name for the property collection.
valueAsBool	Calculates the current value of the property with the specified key and interprets it as an boolean.
valueAsColor	Calculates the current value of the property with the specified key and interprets it as a color.
valueAsDateTime	Calculates the current value of the property with the specified key and interprets it as a datetime.
valueAsDouble	Calculates the current value of the property with the specified key and interprets it as a double.
valueAsInt	Calculates the current value of the property with the specified key and interprets it as an integer.
valueAsString	Calculates the current value of the property with the specified key and interprets it as a string.

Virtual Methods

In PyQGIS, only methods marked as virtual can be safely overridden in a Python subclass of QgsAbstractPropertyCollection. See the FAQ for more details.

readXml	Reads property collection state from an XML element.
writeXml	Writes the current state of the property collection into an XML element

class qgis.core.QgsAbstractPropertyCollection

Bases: object

__init__(name: str | None = '')

Constructor for QgsAbstractPropertyCollection. The name parameter should be set to a descriptive name for the collection.

Parameters:

name (Optional[str] = '')

__init__(a0: QgsAbstractPropertyCollection)

Parameters:

a0 (QgsAbstractPropertyCollection)

abstract clear(self)

Removes all properties from the collection.

abstract hasActiveProperties(self) → bool

Returns True if the collection has any active properties, or False if all properties within the collection are deactivated.

See also

hasDynamicProperties()

Return type:

bool

abstract hasDynamicProperties(self) → bool

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.

See also

hasActiveProperties()

Return type:

bool

abstract hasProperty(self, key: int) → bool

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

Parameters:

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

See also

property()

Return type:

bool

abstract isActive(self, key: int) → bool

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

Parameters:

key (int) – 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.

Return type:

bool

abstract loadVariant(self, configuration: Any, definitions: Dict[int, QgsPropertyDefinition]) → bool

Loads this property collection from a QVariantMap, wrapped in a QVariant. You can use QgsXmlUtils.readVariant to save it to an XML document.

See also

toVariant()

Parameters:

• configuration (Any)

• definitions (Dict[int, QgsPropertyDefinition])

Return type:

bool

name(self) → str

Returns the descriptive name of the property collection.

See also

setName()

Return type:

str

abstract prepare(self, context: QgsExpressionContext = QgsExpressionContext()) → bool

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.

Parameters:

context (QgsExpressionContext = QgsExpressionContext())

Return type:

bool

abstract property(self, key: int) → QgsProperty

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

Parameters:

key (int) – 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.

Return type:

QgsProperty

Returns:

matching property, or null if no matching, active property found.

See also

hasProperty()

abstract propertyKeys(self) → Any

Returns a list of property keys contained within the collection.

Return type:

Any

virtual readXml(self, collectionElem: QDomElement, definitions: Dict[int, QgsPropertyDefinition]) → bool

Reads property collection state from an XML element.

Parameters:

• collectionElem (QDomElement) – source DOM element for property collection’s state

• definitions (Dict[int, QgsPropertyDefinition]) – property definitions

See also

writeXml()

Return type:

bool

abstract referencedFields(self, context: QgsExpressionContext = QgsExpressionContext(), ignoreContext: bool = False) → Set[str]

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

Parameters:

• context (QgsExpressionContext = QgsExpressionContext()) – expression context the properties will be evaluated against.

• ignoreContext (bool = False) – This parameter has been added in QGIS 3.14. When set to True, even fields not set in context’s fields() will be reported - this is useful e.g. with vector tiles where the actual available field names may not be known beforehand.

Return type:

Set[str]

setName(self, name: str | None)

Sets the descriptive name for the property collection.

See also

name()

Parameters:

name (Optional[str])

abstract toVariant(self, definitions: Dict[int, QgsPropertyDefinition]) → Any

Saves this property collection to a QVariantMap, wrapped in a QVariant. You can use QgsXmlUtils.writeVariant to save it to an XML document.

See also

loadVariant()

Parameters:

definitions (Dict[int, QgsPropertyDefinition])

Return type:

Any

abstract value(self, key: int, context: QgsExpressionContext, defaultValue: Any = None) → Any

Returns the calculated value of the property with the specified key from within the collection. If you need the validity of the value (like ok provided from the valueAs* variants) refer to the property() and QgsProperty.value()

Parameters:

• key (int) – 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 (QgsExpressionContext) – expression context to evaluate property against

• defaultValue (Any = None) – default value to return if no matching, active property found or if the property value cannot be calculated

Return type:

Any

Returns:

calculated property value, or default value if property could not be evaluated

See also

valueAsString()

See also

valueAsColor()

See also

valueAsDouble()

See also

valueAsInt()

See also

valueAsBool()

valueAsBool(self, key: int, context: QgsExpressionContext, defaultValue: bool = False)

Calculates the current value of the property with the specified key and interprets it as an boolean.

Parameters:

• key (int) – 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 (QgsExpressionContext) – QgsExpressionContext to evaluate the property for.

• defaultValue (bool = False) -> (bool) – default boolean to return if the property cannot be calculated as a boolean

Returns:

• value parsed to bool

• ok: True if conversion was successful

See also

value()

See also

valueAsDateTime()

See also

valueAsString()

See also

valueAsColor()

See also

valueAsDouble()

See also

valueAsInt()

valueAsColor(self, key: int, context: QgsExpressionContext, defaultColor: QColor | Qt.GlobalColor = QColor())

Calculates the current value of the property with the specified key and interprets it as a color.

Parameters:

• key (int) – 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 (QgsExpressionContext) – QgsExpressionContext to evaluate the property for.

• defaultColor (Union[QColor, Qt.GlobalColor] = QColor()) -> (QColor) – default color to return if the property cannot be calculated as a color

Returns:

• value parsed to color

• ok: True if conversion was successful

See also

value()

See also

valueAsDateTime()

See also

valueAsString()

See also

valueAsDouble()

See also

valueAsInt()

See also

valueAsBool()

valueAsDateTime(self, key: int, context: QgsExpressionContext, defaultDateTime: QDateTime | datetime.datetime = QDateTime())

Calculates the current value of the property with the specified key and interprets it as a datetime.

Parameters:

• key (int) – 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 (QgsExpressionContext) – QgsExpressionContext to evaluate the property for.

• defaultDateTime (Union[QDateTime, datetime.datetime] = QDateTime()) -> (QDateTime) – default datetime to return if the property cannot be calculated as a datetime

Returns:

• value parsed to datetime

• ok: True if conversion was successful

See also

value()

See also

valueAsString()

See also

valueAsColor()

See also

valueAsDouble()

See also

valueAsInt()

See also

valueAsBool()

Added in version 3.14.

valueAsDouble(self, key: int, context: QgsExpressionContext, defaultValue: float = 0)

Calculates the current value of the property with the specified key and interprets it as a double.

Parameters:

• key (int) – 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 (QgsExpressionContext) – QgsExpressionContext to evaluate the property for.

• defaultValue (float = 0) -> (float) – default double to return if the property cannot be calculated as a double

Returns:

• value parsed to double

• ok: True if conversion was successful

See also

value()

See also

valueAsDateTime()

See also

valueAsString()

See also

valueAsColor()

See also

valueAsInt()

See also

valueAsBool()

valueAsInt(self, key: int, context: QgsExpressionContext, defaultValue: int = 0)

Calculates the current value of the property with the specified key and interprets it as an integer.

Parameters:

• key (int) – 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 (QgsExpressionContext) – QgsExpressionContext to evaluate the property for.

• defaultValue (int = 0) -> (int) – default integer to return if the property cannot be calculated as a integer

Returns:

• value parsed to integer

• ok: True if conversion was successful

See also

value()

See also

valueAsDateTime()

See also

valueAsString()

See also

valueAsColor()

See also

valueAsDouble()

See also

valueAsBool()

valueAsString(self, key: int, context: QgsExpressionContext, defaultString: str | None = '')

Calculates the current value of the property with the specified key and interprets it as a string.

Parameters:

• key (int) – 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 (QgsExpressionContext) – QgsExpressionContext to evaluate the property for.

• defaultString (Optional[str] = '') -> (str) – default string to return if the property cannot be calculated as a string

Returns:

• value parsed to string

• ok: True if conversion was successful

See also

value()

See also

valueAsDateTime()

See also

valueAsColor()

See also

valueAsDouble()

See also

valueAsInt()

See also

valueAsBool()

virtual writeXml(self, collectionElem: QDomElement, definitions: Dict[int, QgsPropertyDefinition]) → bool

Writes the current state of the property collection into an XML element

Parameters:

• collectionElem (QDomElement) – destination element for the property collection’s state

• definitions (Dict[int, QgsPropertyDefinition]) – property definitions

See also

readXml()

Return type:

bool