Assigning value to PointerProperty? [resolved]

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1

Edit for brevity and clarity. The short short version is that I can use a PointerProperty and set it via a UI panel, but actually trying to set the value in a python operator suddenly makes the UI panel reading the value throw errors.

I’ve searched around and found a couple of references to this, but I’ll be damned if I can make heads or tails of them, and most are many years outdated anyway, so I figure I should ask here.

In a personal addon I am working on, I’m using a PointerProperty to specify a target for an operation, instead of just a text field with the name. Among other things, this lets me use the eyedropper function to select an object.

Setting values / selecting objects in the UI works fine, both with the dropdown list, and the eyedropper. But when an operator changes the value (in this example, I have a button that sets the variable to point to the active object), suddenly row.prop() stops working.

Specifically, the code that displays the field produces the error:
rna_uiItemR: property not found: TestProps.propertyDisplayTarget

This despite the fact that other calls like
rna_uiItemR: property not found: TestProps.propertyDisplayTarget
work just fine.

Here is my code, stripped down to the bare minimum:

import bpy

class TestProps(bpy.types.PropertyGroup):
    propertyDisplayTarget: bpy.props.PointerProperty(name = "Object", type = bpy.types.Object)
    propertyDisplayUseActiveObject: bpy.props.BoolProperty(name = "Use Active")

class TEST_OT_setPropertyDisplayTargetToActive(bpy.types.Operator):
    """Set property display target object to active"""
    bl_idname = "object.setpropertydisplaytargettoactive"
    bl_label = "Set to active"
    bl_context = "object"
    
    @classmethod
    def poll(cls, context):
        if bpy.context.active_object:
            return True
        else:
            return False

    def execute(self, context):
        TestProps.propertyDisplayTarget = bpy.context.active_object.id_data
        print("#"*7, "set ", TestProps.propertyDisplayTarget)
        return {'FINISHED'}

class TEST_PT_propertiesPanel(bpy.types.Panel):
    """Shows properties of specified object"""
    bl_label = "Object/Bone Properties"
    bl_idname = "SCENE_PT_properties"
    bl_space_type = 'VIEW_3D'
    bl_category = 'Testing'
    bl_region_type = "UI"

    @classmethod
    def poll(cls, context):
        return True

    def draw(self, context):
        layout = self.layout
        scene = bpy.context.scene
        row = layout.row()
        row.label(text = "Test panel")
        row = layout.row()
        if scene.TestProps:
            row = layout.row()
            row.label(text = "Target name is " + scene.TestProps.propertyDisplayTarget.name)
        row = layout.row()        
        row.prop(scene.TestProps, "propertyDisplayTarget")
        row = layout.row()
        row.operator('object.setpropertydisplaytargettoactive')

classes = (TestProps,
            TEST_OT_setPropertyDisplayTargetToActive,
            TEST_PT_propertiesPanel,
            TestProps
            )

def register():
    from bpy.utils import register_class
    for cls in classes:
        register_class(cls)
        bpy.types.Scene.TestProps = bpy.props.PointerProperty(type=TestProps)

def unregister():
    from bpy.utils import unregister_class
    for cls in reversed(classes):
        unregister_class(cls)
        del bpy.types.Scene.TestProps
        
if __name__ == "__main__":
    register()

It works fine until I use the “set to active” button. Then it stops working and spams my console with the error stated above.

Also, I can still access the PointerProperty from the console just fine, it is ONLY the prop field in the UI panel that breaks.

Can anyone explain this to me? Thanks!

2

Hi,
I’m still learning python Blender but I can see somes mistakes in the code :

  • classes contains 2 TestProps
  • in register and unregister function, you don’t need to include bpy.types.Scene.TestProps in the for loop, you just have to call it once
  • in the panel, scene.TestProps.propertyDisplayTarget contains no object at the beginning so the if statement should be

if scene.TestProps.DisplayTarget:

  • in the poll function of the TEST_OT_setPropertyDisplayTargetToActive class, just need this line

return context.active_object != None

  • in the execute function of the TEST_OT_setProperty … class use context.scene.TestProps. The error you mention is here.

So here your code modified:

> import bpy
> 
> class TestProps(bpy.types.PropertyGroup):
>     propertyDisplayTarget: bpy.props.PointerProperty(name = "Object", type = bpy.types.Object)
>     propertyDisplayUseActiveObject: bpy.props.BoolProperty(name = "Use Active")
> 
> class TEST_OT_setPropertyDisplayTargetToActive(bpy.types.Operator):
>     """Set property display target object to active"""
>     bl_idname = "object.setpropertydisplaytargettoactive"
>     bl_label = "Set to active"
>     bl_context = "object"
>     
>     @classmethod
>     def poll(cls, context):
>         return bpy.context.active_object != None
>       
>     def execute(self, context):
>         TestProps = context.scene.TestProps
>         TestProps.propertyDisplayTarget.select_set(state = True)
>         bpy.context.view_layer.objects.active = TestProps.propertyDisplayTarget
>         print("#"*7, "set ", TestProps.propertyDisplayTarget)
>         return {'FINISHED'}
> 
> class TEST_PT_propertiesPanel(bpy.types.Panel):
>     """Shows properties of specified object"""
>     bl_label = "Object/Bone Properties"
>     bl_idname = "SCENE_PT_properties"
>     bl_space_type = 'VIEW_3D'
>     bl_category = 'Testing'
>     bl_region_type = "UI"
> 
>     def draw(self, context):
>         layout = self.layout
>         scene = bpy.context.scene
>         obj = context.active_object
>         row = layout.row()
>         row.label(text = "Test panel")
>         row = layout.row()
>         row = layout.row()
>         if scene.TestProps.propertyDisplayTarget:
>             row.label(text = "Target name is " + scene.TestProps.propertyDisplayTarget.name)
>         else:
>             row.label(text = "Target name is ")
>         row = layout.row()        
>         row.prop(scene.TestProps, "propertyDisplayTarget")
>         row = layout.row()
>         row.operator('object.setpropertydisplaytargettoactive')
> 
> classes = (TestProps,
>             TEST_OT_setPropertyDisplayTargetToActive,
>             TEST_PT_propertiesPanel
>             )
> 
> def register():
>     from bpy.utils import register_class
>     for cls in classes:
>         register_class(cls)
>     bpy.types.Scene.TestProps = bpy.props.PointerProperty(type=TestProps)
> 
> def unregister():
>     from bpy.utils import unregister_class
>     for cls in reversed(classes):
>         unregister_class(cls)
>     del bpy.types.Scene.TestProps
>         
> if __name__ == "__main__":
>     register()
3

Thank you for pointing out those errors. That makes sense, and is a bit embarrassing. I appreciate it! However, the fixed code doesn’t actually do what I am trying to do. Fortunately, fixing the other errors fixes the issue! So I was focusing on the one line that threw the error instead of the rest of the code. Derp.

Again, thanks for your help! :smiley:

So, if anyone else is searching around about the same thing and finds this thread, I’ll leave some extra information.

I think I may have incorrectly explained what I am trying to accomplish, due to bad phrasing. The idea is not to read object propertyDisplayTarget points to, and make the referenced object active.

The thing I am trying to do is to read bpy.context.active_object, and change the value of propertyDisplayTarget to whatever object is active when the operator is executed.

Deleting two lines from and adding one to the fixed code accomplishes what I meant to do.

import bpy

class TestProps(bpy.types.PropertyGroup):
    propertyDisplayTarget: bpy.props.PointerProperty(name = "Object", type = bpy.types.Object)
    propertyDisplayUseActiveObject: bpy.props.BoolProperty(name = "Use Active")

class TEST_OT_setPropertyDisplayTargetToActive(bpy.types.Operator):
    """Set property display target object to active"""
    bl_idname = "object.setpropertydisplaytargettoactive"
    bl_label = "Set to active"
    bl_context = "object"
    
    @classmethod
    def poll(cls, context):
        return bpy.context.active_object != None
      
    def execute(self, context):
        TestProps = context.scene.TestProps
        TestProps.propertyDisplayTarget = bpy.context.active_object
        print("#"*7, "set to", TestProps.propertyDisplayTarget) #for testing purposes
        return {'FINISHED'}

class TEST_PT_propertiesPanel(bpy.types.Panel):
    """Shows properties of specified object"""
    bl_label = "Object/Bone Properties"
    bl_idname = "SCENE_PT_properties"
    bl_space_type = 'VIEW_3D'
    bl_category = 'Testing'
    bl_region_type = "UI"

    def draw(self, context):
        layout = self.layout
        scene = bpy.context.scene
        obj = context.active_object
        row = layout.row()
        row.label(text = "Test panel")
        row = layout.row()
        if scene.TestProps.propertyDisplayTarget:
            row.label(text = "Target name is " + scene.TestProps.propertyDisplayTarget.name)
        else:
            row.label(text = "Target name is ")
        row = layout.row()        
        row.prop(scene.TestProps, "propertyDisplayTarget")
        row = layout.row()
        row.operator('object.setpropertydisplaytargettoactive')

classes = (TestProps,
            TEST_OT_setPropertyDisplayTargetToActive,
            TEST_PT_propertiesPanel
            )

def register():
    from bpy.utils import register_class
    for cls in classes:
        register_class(cls)
    bpy.types.Scene.TestProps = bpy.props.PointerProperty(type=TestProps)

def unregister():
    from bpy.utils import unregister_class
    for cls in reversed(classes):
        unregister_class(cls)
    del bpy.types.Scene.TestProps
        
if __name__ == "__main__":
    register()