Here is my code:

from vanilla import Window
from mojo.UI import SpaceCenter

class StupidSpaceCenter(SpaceCenter):

    def layersChanged(self, sender):
        print('layer has changed')
        # I will put a lot of code here

class StupidSpaceCenterWindow(object):
 
    def __init__(self, font):
        self.font = font
        self.w = Window((800, 600), 'Sandwich Space Center', minSize=(600, 400), autosaveName='com.rb.StupidSpaceCenterWindow')
        self.w.spaceCenter = StupidSpaceCenter((0, 0, -0, -0), self.font, glyphNames='ABC')
        self.w.open()

StupidSpaceCenterWindow(CurrentFont().naked())

and this is an error that I get whenever I change some spacing.

Traceback (most recent call last):
 File "lib/doodleDelegate.pyc", line 96, in sendEvent_
 File "lib/UI/spaceCenter/multiLineScrollScrollView.pyc", line 1750, in mouseDragged_
 File "lib/fontObjects/doodleGlyph.pyc", line 157, in _set_rightMargin
 File "/Applications/RoboFont.app/Contents/Resources/lib/python3.7/defcon/objects/base.py", line 169, in releaseHeldNotifications
 dispatcher.releaseHeldNotifications(observable=self, notification=notification)
 File "/Applications/RoboFont.app/Contents/Resources/lib/python3.7/defcon/tools/notifications.py", line 260, in releaseHeldNotifications
 self.postNotification(notification, observableRef(), data)
 File "/Applications/RoboFont.app/Contents/Resources/lib/python3.7/defcon/tools/notifications.py", line 201, in postNotification
 callback(notificationObj)
 File "lib/UI/spaceCenter/__init__.pyc", line 1005, in _glyphWidthChanged
 File "lib/UI/spaceCenter/multiLineScrollScrollView.pyc", line 2457, in _updatesBlocked
 File "lib/UI/spaceCenter/multiLineScrollScrollView.pyc", line 718, in isFirstResponder
AttributeError: 'NoneType' object has no attribute 'isMainWindow'

How can I fix it? What am I doing wrong?
Maybe it is a bug (because this example from the documentation throws the same error)?

Thanks, guys in advance for ur help
Cheers

What version of RF are you using?
Does this happen after a fresh restart?
Does this happen in safe mode? (start up with shift down, no extension, start up script will be installed)

When I open it with the safe mode (by the way, I never knew about it, great feature, thanks for telling me about it), there is nothing in the output.

small question:
layersChanged is run on the edit of the glyph (like glyph.addObserver(self, 'glyphHasChanged', 'Glyph.Changed')) or whenever I'm changing the active layer?

My version of the RF is the last beta

the issue occurs when I try to print out the sender in the layerChanged.

before I put sender in the print statement, inside of the layerChanged, nothing happened when I've edited the glyph. Nothing also printed (even if the debug print statement was inside this callback).

What is it you would like to achieve?

Since the traceback is gone in safe mode, I assume an other extension, script is interfering.

Or a reference of an closed space center has still active observers on the defcon Glyph.WidthChanged notification.

In order to do that I'm trying to create a system of observers. Now I changed approach and I'm using Glyph.WidthChanged

euhm use alt + drag metrics :) to apply the change to all layers... both in glyph view as in a space center

HAHAHA, thanks!!!

Of course, I had no idea about that.

Damn, I love it, I already made a sophisticated observer system, which checks which space center is being used, activates Glyph.LeftMarginDidChange etc, etc…

At least now I'm also able to use normal step-by-step spacing for all of the layers :D, not only dragging