Update Float Property Based on Selected Object

Question

I'm writing an add-on and have a float property which drives the thickness attribute of a solidify modifier for the selected object. Currently, the float property displays the last value assigned by the user using that property. Instead, when the user selects an object, I'd like the float property to display the value for that object's solidify modifier.

I've written this function but from what I've read, this won't work anywhere within the draw or poll functions for the panel.

def SyncThickness():
    myprops = bpy.data.scenes["Scene"].my_properties
    if len(bpy.context.selected_objects) >=1:
        myprops.thickness_float = bpy.context.selected_objects[0].modifiers["Solidify"].thickness
    else:
        myprops.thickness_float = 0

Is there anyway to call this function whenever a different object is selected? Or is a different approach required?

Thanks

Chris

Answer 1

Use Application Handlers (bpy.app.handlers)

import bpy
from bpy.app.handlers import persistent

@persistent
def update_function(dummy):
    print("run...")
    # when select a object or depsgraph data changed, it will run

bpy.app.handlers.depsgraph_update_post.append(update_function)

API link: https://docs.blender.org/api/current/bpy.app.handlers.html?highlight=load_post#bpy.app.handlers.load_post

Answer 2

You could just utilize the modifier property directly:

import bpy


class VIEW3D_PT_test(bpy.types.Panel):
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'
    bl_category = "Test Panel"
    bl_idname = "VIEW3D_PT_test_panel_1"
    bl_label = "Test Panel 1"


    def draw(self, context):
        layout = self.layout
        box = layout.box()
        col = box.column(align=True)
        col.label(text="Sub Panel label")
        
        obj =context.object
        if obj and obj.modifiers:
            sol_mods = [m for m in obj.modifiers if m.type =='SOLIDIFY']
        if not sol_mods:
            return
        for m in sol_mods:
            col.label(text=f"{m.name}")
            col.prop(m, "thickness")


classes = [VIEW3D_PT_test,
        ]

def register():
    for cls in classes:
        bpy.utils.register_class(cls)


def unregister():
    for cls in classes:
        bpy.utils.unregister_class(cls)

if __name__ == "__main__":
    register()