Setting the Default Value of a Float Property Dynamically

Question

I am updating the active object's location.x with a FloatProperty with the following code.

How can I change the value of the FloatProperty slider to the active_object's current location.x when the active_object changes?

Thank you!

import bpy
class SomePanel( bpy.types.Panel ):
    bl_label = "Property panel"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"
def draw(self, context):
    layout = self.layout
    scn = context.scene
    layout.prop( scn, 'someValue' )


def whenUpdate( self, context ):
    if context.active_object:
        context.active_object.location.x = self.someValue
    print( 'update', self.someValue )
def register():
    bpy.types.Scene.someValue = bpy.props.FloatProperty( 
        name = "Float", 
        description = "Enter a float", min = -100, max = 100,
        update = whenUpdate ) #Assign the update function here
    bpy.utils.register_class(SomePanel)
def unregister():
    bpy.utils.unregister_class(SomePanel)
    del bpy.types.Scene.someValue
if name == "main":
    register()

Hello ! Just a thought, wouldn't it be easier to define a property with a getter that fetches the active object's x location value ? — Gorgious, Dec 06 '21 at 08:14
Hello @Gorgious, thank you for the reply. It might be easier! Do you mean a PropertyGroup class? If so, can I access the scene's someValue variable and the active_object from there? — Dr. Pontchartrain, Dec 06 '21 at 08:49

Gorgious · Accepted Answer · 2021-12-06T09:01:48.243

1

If I understood the problem correctly, you can use Getter / Setter functions to achieve your goal.

import bpy
def get_value(self):
    return bpy.context.active_object.location.x
def set_value(self, value):
    bpy.context.active_object.location.x = value
if name == "main":
    bpy.types.Scene.someValue = bpy.props.FloatProperty(get=get_value, set=set_value)

Of course you'll have to add safeguards so you don't try to run the functions if there is no active object.

edited Dec 06 '21 at 09:01

answered Dec 06 '21 at 08:59

Gorgious

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This is perfect, thank you!! – Dr. Pontchartrain Dec 06 '21 at 09:00

Dr. Pontchartrain · Answer 2 · 2021-12-06T08:39:16.543

I've found an answer via from Detective bpy on the Blender Community Discord. They provided a link to this post: https://blender.stackexchange.com/a/239606

Which led me to this solution:

import bpy
def msgbus_callback(*arg):
    bpy.context.scene.someValue = bpy.context.selected_objects[0].location.x
def subscribe_to_obj(): 
    bpy.msgbus.subscribe_rna(
        key=(bpy.types.LayerObjects, 'active'),
        owner=bpy,
        args=('something, if you need',),
        notify=msgbus_callback
        )
class VIEW3D_PT_SomePanel( bpy.types.Panel ):
    bl_label = "Property panel"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"
def draw(self, context):
    layout = self.layout
    scn = context.scene
    layout.prop( scn, 'someValue' )


def whenUpdate( self, context ):
    if context.active_object:
        context.active_object.location.x = self.someValue
    print( 'update', self.someValue )
def register():
    bpy.types.Scene.someValue = bpy.props.FloatProperty( 
        name = "Float", 
        description = "Enter a float", min = -100, max = 100,
        update = whenUpdate ) #Assign the update function here
    bpy.utils.register_class(VIEW3D_PT_SomePanel)
    subscribe_to_obj()
def unregister():
    bpy.utils.unregister_class(VIEW3D_PT_SomePanel)
    del bpy.types.Scene.someValue
if name == "main":
    register()

Setting the Default Value of a Float Property Dynamically

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