Doubleclick in Table and Tree with data==None triggers IndexError

[areslagae]

Describe the bug

doubleclick in table with data==None triggers IndexError

example below results in error below

this might be by design, but since None is an acceptable value for data per the documentation, and it makes perfect sense to have an empty table in an application (mine is empty until the user triggers a db query), this behavior is unexpected to me

not a disaster - why would a user click there anyway If there is no data - but also not great since it crashes the application

Traceback (most recent call last):
  File ".../.venv/lib/python3.14/site-packages/rubicon/objc/api.py", line 412, in __call__
    result = self.py_method(py_self, *args)
  File ".../.venv/lib/python3.14/site-packages/toga_cocoa/widgets/table.py", line 127, in onDoubleClick_
    clicked = self.interface.data[self.clickedRow]
  File ".../.venv/lib/python3.14/site-packages/toga/sources/list_source.py", line 135, in __getitem__
    return self._data[index]
IndexError: list index out of range

Steps to reproduce

import toga

class MyApp(toga.App):
    def startup(self):
        self.main_window = toga.MainWindow()
        self.main_window.content = toga.Table(
            headings=["Name", "Age"],
            # data=[
            #     ("Arthur Dent", 42),
            #     ("Ford Prefect", 37),
            #     ("Tricia McMillan", 38),
            # ],
            data=None,
            multiple_select=False,
        )        
        self.main_window.show()

if __name__ == '__main__':
    app = MyApp("Realistic App", "org.beeware.realistic")
    app.main_loop()

Expected behavior

no exception

Screenshots

No response

Environment

macOS 24.6.0
Python 3.14.0 (main, Oct 7 2025, 09:34:52) [Clang 17.0.0 (clang-1700.0.13.3)] on darwin
Toga: toga-0.5.2

Logs

Additional context

No response

[freakboy3742]

Thanks for the report. From a quick inspection, there's actually 2 bugs here, both with the same cause.

When you double click on a macOS table on a non-data row, macOS returns "-1" as the index.

When there's no data, you get an exception, as you've shown in your stack trace. But when there is data, the last selected row is returned.

So - the fix here would seem to be qualifying that the index is >= 0 before trying to look up data.

[freakboy3742]

Also - it would be worth checking if Tree and DetailedList have the same issue - they share some similarities, so it seems possible they might.

[areslagae]

Tree also has an issue, albeit a different one (AttributeError: 'NoneType' object has no attribute 'attrs'), but probably same issue

import toga

class MyApp(toga.App):
    def startup(self):
        self.main_window = toga.MainWindow()
        self.main_window.content = toga.Tree(
            headings=["Name", "Age"],
            data={
                # "Earth": {
                # ("Arthur Dent", 42): None,
                # },
                # "Betelgeuse Five": {
                # ("Ford Prefect", 37): None,
                # ("Zaphod Beeblebrox", 47): None,
                # },
            }
        )
        self.main_window.show()

if __name__ == '__main__':
    app = MyApp("Realistic App", "org.beeware.realistic")
    app.main_loop()

Exception ignored while calling ctypes callback function <rubicon.objc.api.objc_method object at 0x102bbe690>:
Traceback (most recent call last):
  File ".../.venv/lib/python3.14/site-packages/rubicon/objc/api.py", line 412, in __call__
    result = self.py_method(py_self, *args)
  File ".../.venv/lib/python3.14/site-packages/toga_cocoa/widgets/tree.py", line 169, in onDoubleClick_
    node = self.itemAtRow(self.clickedRow).attrs["node"]
AttributeError: 'NoneType' object has no attribute 'attrs'

[areslagae]

toga.DetailedList seems fine at first sight

import toga

class MyApp(toga.App):
    def startup(self):
        self.main_window = toga.MainWindow()
        self.main_window.content = toga.DetailedList(
            data=[
            ]
        )
        self.main_window.show()

if __name__ == '__main__':
    app = MyApp("Realistic App", "org.beeware.realistic")
    app.main_loop()

[freakboy3742]

Thanks for that detail.

As an aside - if you use triple backticks around code samples, Github will present them in a way that looks like code - I've edited your last two comments to use this syntax; if you click the edit button (from the three dots menu top right on the comment) you can see the syntax change that I made.

[MhussainD4772]

Hi can I take this issue up ?
Could you please assign this to me

[freakboy3742]

@MhussainD4772 As noted elsewhere - we don't assign issues. However, I'd also suggest that you only try to work on one ticket at a time. It doesn't matter which one... but especially on your first ticket, it's helpful to go slow so you can get familiar with our processes and procedures for contribution.

[MhussainD4772]

@freakboy3742 Yes sir! Just wasn't sure, how to start so was kinda jumping around, I'll start with this ticket. And progress slowly. Thanks

[freakboy3742]

It turns out this problem exists for both trees and tables. Also, it can occur when the table does have data, if you click on the table/tree header, or in an empty row (i.e., below the last row of data if there's less data than the table has space to show).