Property/en

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Introduction

A property is a piece of information like a number or a text string that is attached to a FreeCAD document or an object in a document. Public properties can be viewed and modified in the Property View.

Properties play a very important role in FreeCAD. As objects in FreeCAD are "parametric", this means that their behavior is defined by their properties, and how these properties are used as input for their class methods. See also FeaturePython Custom Properties and PropertyLink: InList and OutList

All property types

Custom scripted objects can use any of the property types defined in the base system:

Name Unit (if any) Remark
Acceleration m/s^2
AmountOfSubstance mol
Angle °
Area m^2
Bool
BoolList
Color
ColorList
CurrentDensity A/m^2
Density kg/m^3
Direction
DissipationRate m^2/s^3
Distance m
DynamicViscosity Pa*s
ElectricalCapacitance F
ElectricalConductance S
ElectricalConductivity S/m
ElectricalInductance H
ElectricalResistance Ohm
ElectricCharge C
ElectricCurrent A
ElectricPotential V
Enumeration
ExpressionEngine
File
FileIncluded
Float
FloatConstraint
FloatList
Font
Force N
Frequency Hz
HeatFlux W/m^2
Integer
IntegerConstraint
IntegerList
IntegerSet
InverseArea 1/m^2
InverseLength 1/m
InverseVolume 1/m^3
KinematicViscosity m^2/s
Length m
Link
LinkChild
LinkGlobal
LinkHidden
LinkList
LinkListChild
LinkListGlobal
LinkListHidden
LinkSub
LinkSubChild
LinkSubGlobal
LinkSubHidden
LinkSubList
LinkSubListChild
LinkSubListGlobal
LinkSubListHidden
LuminousIntensity cd
MagneticFieldStrength A/m
MagneticFlux Wb or V*s
MagneticFluxDensity T
Magnetization A/m
Map
Mass kg
Material
MaterialList
Matrix
PartShape a Part property, is accessed as
Part::PropertyPartShape
Path
Percent
PersistentObject
Placement
PlacementLink
PlacementList
Position
Power W
Precision
Pressure Pa
PythonObject
Quantity
QuantityConstraint
Rotation
ShearModulus Pa
SpecificEnergy m^2/s^2 or J/kg
SpecificHeat J/kg/K
Speed m/s
Stiffness m/s^2
Stress Pa
String
StringList
Temperature K
ThermalConductivity W/m/K
ThermalExpansionCoefficient 1/K
ThermalTransferCoefficient W/m^2/K
Time s
UltimateTensileStrength Pa
UUID
VacuumPermittivity s^4*A^2 / (m^3*kg)
Vector
VectorDistance
VectorList
Velocity m/s
Volume l or m^3
VolumeFlowRate l/s or m^3/s
VolumetricThermalExpansionCoefficient 1/K
Work J
XLink
XLinkList
XLinkSub
XLinkSubList
YieldStrength Pa
YoungsModulus Pa


Internally, the property name is prefixed with App::Property: 

App::PropertyBool
App::PropertyFloat
App::PropertyFloatList
...

Remember that these are property types. A single object may have many properties of the same type, but with different names.

For example: 

obj.addProperty("App::PropertyFloat", "Length")
obj.addProperty("App::PropertyFloat", "Width")
obj.addProperty("App::PropertyFloat", "Height")

This indicates an object with three properties of type "Float", named "Length", "Width", and "Height", respectively.

Scripting

See also: FreeCAD scripting basics

A scripted object is created first, and then properties are assigned. 

obj = App.ActiveDocument.addObject("Part::Feature", "CustomObject")

obj.addProperty("App::PropertyFloat", "Velocity", "Parameter", "Body speed")
obj.addProperty("App::PropertyBool", "VelocityEnabled", "Parameter", "Enable body speed")

In general, Data properties are assigned by using the object's addProperty() method. On the other hand, View properties are normally provided automatically by the parent object from which the scripted object is derived.

For example:

Nevertheless, View properties can also be assigned using the view provider object's addProperty() method. 

obj.ViewObject.addProperty("App::PropertyBool", "SuperVisibility", "Base", "Make the object glow")

Source code

In the source code, properties are located in various src/App/Property* files.

They are imported and initialized in src/App/Application.cpp. 

#include "Property.h"
#include "PropertyContainer.h"
#include "PropertyUnits.h"
#include "PropertyFile.h"
#include "PropertyLinks.h"
#include "PropertyPythonObject.h"
#include "PropertyExpressionEngine.h"


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