Subgroup: Property
Class: QgsProperty¶
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class
qgis.core.
QgsProperty
¶ Bases:
sip.wrapper
A store for object properties.
QgsProperty objects are used for storing properties for objects, which can then be transformed to a QVariant value by evaluating them against a supplied
QgsExpressionContext
. Multiple QgsProperty objects can be grouped using a QgsPropertyCollection for easier bulk storage, retrieval and evaluation.QgsProperty objects are implicitly shared and can be inexpensively copied.
New in version 3.0: Methods
asExpression
Returns an expression string representing the state of the property, or an empty convertToTransformer
Attempts to convert an existing expression based property to a base expression with corresponding transformer. expressionString
Returns the expression used for the property value. field
Returns the current field name the property references. fromExpression
Returns a new ExpressionBasedProperty created from the specified expression. fromField
Returns a new FieldBasedProperty created from the specified field name. fromValue
Returns a new StaticProperty created from the specified value. isActive
Returns whether the property is currently active. loadVariant
Loads this property from a QVariantMap, wrapped in a QVariant. prepare
Prepares the property against a specified expression context. propertyType
Returns the property type. referencedFields
Returns the set of any fields referenced by the property for a specified expression context. setActive
Sets whether the property is currently active. setExpressionString
Sets the expression to use for the property value. setField
Sets the field name the property references. setStaticValue
Sets the static value for the property. setTransformer
Sets an optional transformer to use for manipulating the calculated values for the property. staticValue
Returns the current static value for the property. toVariant
Saves this property to a QVariantMap, wrapped in a QVariant. transformer
Returns the existing transformer used for manipulating the calculated values for the property, if set. value
Calculates the current value of the property, including any transforms which are set for the property valueAsBool
Calculates the current value of the property and interprets it as an boolean. valueAsColor
Calculates the current value of the property and interprets it as a color. valueAsDouble
Calculates the current value of the property and interprets it as a double. valueAsInt
Calculates the current value of the property and interprets it as an integer. valueAsString
Calculates the current value of the property and interprets it as a string. Attributes
ExpressionBasedProperty
FieldBasedProperty
InvalidProperty
StaticProperty
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ExpressionBasedProperty
= 3¶
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FieldBasedProperty
= 2¶
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InvalidProperty
= 0¶
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StaticProperty
= 1¶
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class
Type
¶ Bases:
int
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asExpression
(self) → str¶ Returns an expression string representing the state of the property, or an empty string if the property could not be converted to an expression
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convertToTransformer
(self) → bool¶ Attempts to convert an existing expression based property to a base expression with corresponding transformer. Returns true if conversion was successful. Note that calling this method requires multiple parsing of expressions, so it should only be called in non-performance critical code.
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expressionString
(self) → str¶ Returns the expression used for the property value. If the property is not a ExpressionBasedProperty this will return an empty string.
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field
(self) → str¶ Returns the current field name the property references. If the property is not a FieldBasedProperty this will return an empty string.
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fromExpression
(expression: str, isActive: bool = True) → QgsProperty¶ Returns a new ExpressionBasedProperty created from the specified expression.
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fromField
(fieldName: str, isActive: bool = True) → QgsProperty¶ Returns a new FieldBasedProperty created from the specified field name.
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fromValue
(value: Any, isActive: bool = True) → QgsProperty¶ Returns a new StaticProperty created from the specified value.
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isActive
(self) → bool¶ Returns whether the property is currently active.
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loadVariant
(self, property: Any) → bool¶ Loads this property from a QVariantMap, wrapped in a QVariant. You can use QgsXmlUtils.readVariant to load it from an XML document.
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prepare
(self, context: QgsExpressionContext = QgsExpressionContext()) → bool¶ Prepares the property against a specified expression context. Calling prepare before evaluating the property multiple times allows precalculation of expensive setup tasks such as parsing expressions. Returns true if preparation was successful.
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propertyType
(self) → QgsProperty.Type¶ Returns the property type.
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referencedFields
(self, context: QgsExpressionContext = QgsExpressionContext()) → Set[str]¶ Returns the set of any fields referenced by the property for a specified expression context.
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setActive
(self, active: bool)¶ Sets whether the property is currently active.
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setExpressionString
(self, expression: str)¶ Sets the expression to use for the property value. Calling this will transform the property into an ExpressionBasedProperty.
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setField
(self, field: str)¶ Sets the field name the property references. Calling this will transform the property into an FieldBasedProperty.
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setStaticValue
(self, value: Any)¶ Sets the static value for the property. Calling this will transform the property into an StaticProperty.
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setTransformer
(self, transformer: QgsPropertyTransformer)¶ Sets an optional transformer to use for manipulating the calculated values for the property.
Parameters: transformer – transformer to install. Ownership is transferred to the property, and any existing transformer will be deleted. Set to null to remove an existing transformer.
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staticValue
(self) → Any¶ Returns the current static value for the property. If the property is not a StaticProperty this will return an invalid variant.
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toVariant
(self) → Any¶ Saves this property to a QVariantMap, wrapped in a QVariant. You can use QgsXmlUtils.writeVariant to save it to an XML document.
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transformer
(self) → QgsPropertyTransformer¶ Returns the existing transformer used for manipulating the calculated values for the property, if set.
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value
(self, context: QgsExpressionContext, defaultValue: Any = None) → Tuple[Any, bool]¶ Calculates the current value of the property, including any transforms which are set for the property
Parameters: context – QgsExpressionContext to evaluate the property for. The variables and functions contained in the expression context can be used to alter the calculated value for the property, so that a property is able to respond to the current environment, layers and features within QGIS. :param defaultValue: default value to return if the property is not active or cannot be calculated :param ok: if specified, will be set to true if conversion was successful
Returns: calculated value for property See also
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valueAsBool
(self, context: QgsExpressionContext, defaultValue: bool = False) → Tuple[bool, bool]¶ Calculates the current value of the property and interprets it as an boolean.
Parameters: - context – QgsExpressionContext to evaluate the property for.
- defaultValue – default boolean to return if the property cannot be calculated as an boolean
- ok – if specified, will be set to true if conversion was successful
Returns: value parsed to boolean
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valueAsColor
(self, context: QgsExpressionContext, defaultColor: Union[QColor, Qt.GlobalColor, QGradient] = QColor()) → Tuple[QColor, bool]¶ Calculates the current value of the property and interprets it as a color.
Parameters: - context – QgsExpressionContext to evaluate the property for.
- defaultColor – default color to return if the property cannot be calculated as a color
- ok – if specified, will be set to true if conversion was successful
Returns: value parsed to color
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valueAsDouble
(self, context: QgsExpressionContext, defaultValue: float = 0) → Tuple[float, bool]¶ Calculates the current value of the property and interprets it as a double.
Parameters: - context – QgsExpressionContext to evaluate the property for.
- defaultValue – default double to return if the property cannot be calculated as a double
- ok – if specified, will be set to true if conversion was successful
Returns: value parsed to double
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valueAsInt
(self, context: QgsExpressionContext, defaultValue: int = 0) → Tuple[int, bool]¶ Calculates the current value of the property and interprets it as an integer.
Parameters: - context – QgsExpressionContext to evaluate the property for.
- defaultValue – default integer to return if the property cannot be calculated as an integer
- ok – if specified, will be set to true if conversion was successful
Returns: value parsed to integer
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valueAsString
(self, context: QgsExpressionContext, defaultString: str = '') → Tuple[str, bool]¶ Calculates the current value of the property and interprets it as a string.
Parameters: - context – QgsExpressionContext to evaluate the property for.
- defaultString – default string to return if the property cannot be calculated as a string
- ok – if specified, will be set to true if conversion was successful
Returns: value parsed to string
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