KivyMD crashes if anchor is set to top when MDNavagationRail has neither MenuButton nor FabButton.

[mnishig]

Description of the Bug

My app has some MDNavigationRailItem only and set anchor is top, KivyMD is crashed with message “attributeError: ‘NoneType’ object has no attribute 'y'”.

Reproduce Code

These are almost same of document's example expect add "anchor: 'top"

from kivy.app import App
from kivy.lang import Builder
from kivy.properties import StringProperty

from kivymd.app import MDApp
from kivymd.uix.navigationrail import MDNavigationRailItem

KV = '''
<CommonNavigationRailItem>
    MDNavigationRailItemIcon:
        icon: root.icon

    MDNavigationRailItemLabel:
        text: root.text

MDBoxLayout:
    MDNavigationRail:
        type: "selected"
        anchor: 'top'

        # MDNavigationRailMenuButton:
        #     icon: "menu"

        # MDNavigationRailFabButton:
        #     icon: "home"

        CommonNavigationRailItem:
            icon: "format-list-bulleted"
            text: "file list"

        CommonNavigationRailItem:
            icon: 'eraser'
            text: 'eraser'

    MDScreen:
        md_bg_color: self.theme_cls.secondaryContainerColor
'''

class CommonNavigationRailItem(MDNavigationRailItem):
    text = StringProperty()
    icon = StringProperty()

class MDRailApp(MDApp):
    def build(self):
        return Builder.load_string(KV)

MDRailApp().run()

log

[INFO   ] [Base        ] Leaving application in progress...
 Traceback (most recent call last):
   File "/media/mnishi/opt/ws-sf/ui/md-nrail.py", line 51, in <module>
     MDRailApp().run()
   File "/media/mnishi/opt/ws-sf/ui/.venv/lib/python3.12/site-packages/kivy/app.py", line 956, in run
     runTouchApp()
   File "/media/mnishi/opt/ws-sf/ui/.venv/lib/python3.12/site-packages/kivy/base.py", line 574, in runTouchApp
     EventLoop.mainloop()
   File "/media/mnishi/opt/ws-sf/ui/.venv/lib/python3.12/site-packages/kivy/base.py", line 339, in mainloop
     self.idle()
   File "/media/mnishi/opt/ws-sf/ui/.venv/lib/python3.12/site-packages/kivy/base.py", line 379, in idle
     Clock.tick()
   File "/media/mnishi/opt/ws-sf/ui/.venv/lib/python3.12/site-packages/kivy/clock.py", line 733, in tick
     self.post_idle(ts, self.idle())
   File "/media/mnishi/opt/ws-sf/ui/.venv/lib/python3.12/site-packages/kivy/clock.py", line 776, in post_idle
     self._process_events()
   File "kivy/_clock.pyx", line 620, in kivy._clock.CyClockBase._process_events
   File "kivy/_clock.pyx", line 653, in kivy._clock.CyClockBase._process_events
   File "kivy/_clock.pyx", line 649, in kivy._clock.CyClockBase._process_events
   File "kivy/_clock.pyx", line 218, in kivy._clock.ClockEvent.tick
   File "/media/mnishi/opt/ws-sf/ui/.venv/lib/python3.12/site-packages/kivymd/uix/navigationrail/navigationrail.py", line 770, in set_top_pos
     anchor_button.y
 AttributeError: 'NoneType' object has no attribute 'y'

cause

MDNavigationRail.py decide anchor y value by _check_anchor() method.
if both MenuButton and FacButton are nothing, anchor_button set None in _check_anchor().

work around

I’ｍ not sure the correct anchor y criteria, so I patch based on height of MDNavigationRail.

    def _check_anchor(self, *args):
        def set_top_pos(*args):
            anchor_y = 0
            if (
                self.fab_button
                and not self.menu_button
                or self.fab_button
                and self.menu_button
            ):
                anchor_button = self.fab_button
                anchor_y = self.fab_button.y
            elif self.menu_button and not self.fab_button:
                anchor_y = self.menu_button.y

            # both MenuButton and FabButton dose not exist  CASE
            else:
                anchor_y = self.height

            self.ids.box_items.y = (
                anchor_y
                - (len(self.ids.box_items.children) * dp(56))
                - dp(56)
            )

        if self.anchor == "center":
            self.ids.box_items.pos_hint = {"center_y": 0.5}
        elif self.anchor == "top":
            Clock.schedule_once(set_top_pos)
        elif self.anchor == "bottom":
            self.ids.box_items.y = dp(56)

        if self.anchor == "center":
            self.ids.box_items.pos_hint = {"center_y": 0.5}
        elif self.anchor == "top":
            Clock.schedule_once(set_top_pos)
        elif self.anchor == "bottom":
            self.ids.box_items.y = dp(56)

$ diff kivymd/kivymd/uix/navigationrail/navigationrail.py ./navigationrail.py

747c747
<             anchor_button = None
---
>             anchor_y = 0
754a755
>                 anchor_y = self.fab_button.y
756c757,759
<                 anchor_button = self.menu_button
---
>                 anchor_y = self.menu_button.y
>             else:
>                 anchor_y = self.height
759c762
<                 anchor_button.y
---

Versions

• OS: Linux Mint 22 (wilma) , cat /etc/upstream-release/lsb-release >> Ubuntu 24.04
• Python: 3.12.3
• Kivy: v2.3.0
• KivyMD: 2.0.1.dev0, git-5ff9d0d