AttributeError: 'NoneType' object has no attribute 'title'

[jlij]

Although the selected value can be obtained, it always reports an error?
Must getattr be used?
widget. selection. title can be used directly？

[freakboy3742]

You’ve provided absolutely no context for this question, so it’s impossible to answer. You haven’t told us which widget you’re using, or how you’re using it. Without details, we can’t determine if you’ve found a legitimate bug, or it’s an error of usage.

[mhsmith]

Please post the full stack trace, and the relevant sections of your code

[jlij]

import toga
from toga.constants import COLUMN
from toga.style import Pack

bee_translations = [
    {"icon": None, "title": "Yoruba", "subtitle": "Bee"},
    {"icon": None, "title": "Chinese", "subtitle": "蜜蜂"},
]


class ExampleDetailedListApp(toga.App):
    # Detailed list callback functions
    def on_select_handler(self, widget):
        row = widget.selection
        print(row.title)

    def startup(self):
        self.main_window = toga.MainWindow()
        self.dl = toga.DetailedList(
            data=bee_translations,
            on_select=self.on_select_handler,
            style=Pack(flex=1),
        )

        # Outermost box
        outer_box = toga.Box(
            children=[self.dl],
            style=Pack(
                flex=1,
                direction=COLUMN,
                padding=10,
            ),
        )

        # Add the content on the main window
        self.main_window.content = outer_box

        # Show the main window
        self.main_window.show()


def main():
    return ExampleDetailedListApp("Detailed List", "org.beeware.widgets.detailedlist")


if __name__ == "__main__":
    app = main()
    app.main_loop()

---

WARNING: Can't find icon resources\detailedlist; falling back to default icon
Yoruba
Error in handler: 'NoneType' object has no attribute 'title'
Traceback (most recent call last):
  File "C:\Users\Administrator\Desktop\number\venv\Lib\site-packages\toga\handlers.py", line 80, in _handler
    result = handler(interface, *args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Administrator\Desktop\number\test.py", line 15, in on_select_handler
    print(row.title)
          ^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'title'
Chinese

[jlij]

[mhsmith]

As the documentation says, widget.selection returns None if no row is currently selected, so your code will have to handle that.

On some platforms, it's possible that there will be an intermediate None state every time the selection switches from one row to another.