`selected=None` does not work in `ui.update_selectize` when `multiple=False`

[ME-researchgroup]

Hi!

I noticed that when I update the inputs for ui.input_selectize using ui.update_selectize the first option will still get selected when providing selected=None.

This issue only occurs when multiple has been set to False in ui.input_selectize. It works as expected when multiple=True.

This works as expected:

# UI
ui.input_selectize(
            "example1",
            "Works as expected",
            choices=[],
            multiple=True,
            selected=None,
        ),

# Server
ui.update_selectize(
                "example1",
                choices=["Option1", "Option2"],
                selected=None,
            )

This will automatically select Option1:

# UI
ui.input_selectize(
            "example2",
            "Unexpected behavior",
            choices=[],
            multiple=False,
            selected=None,
        ),

# Server
ui.update_selectize(
                "example2",
                choices=["Option1", "Option2"],
                selected=None,
            )

[gadenbuie]

Hi @ME-researchgroup and thanks for the report! I can reproduce the issue. I can also give you a quick solution: include "" in the choices of the second example:

ui.update_selectize(
    "example2",
    choices=["", "Option1", "Option2"],
    selected=None,
)

Here's an example app on shinylive.io demonstrating the behavior I observed:

• When multiple=True and selected=None, an empty selection is allowed, even if "" isn't in the choices.
• When multiple=False and selected=None, an empty selection is not allowed unless "" is in the choices.

[ME-researchgroup]

Thank you for your quick response. The solution works for me as well.

[gadenbuie]

No problem! I'm going to re-open this to remind us to take a look at the API to make sure it's consistent or to see if we need to update our docs in some way.

[ME-researchgroup]

@gadenbuie FYI, this no longer seems to work in shiny version 0.10.x

Hi @ME-researchgroup and thanks for the report! I can reproduce the issue. I can also give you a quick solution: include "" in the choices of the second example:

ui.update_selectize(
    "example2",
    choices=["", "Option1", "Option2"],
    selected=None,
)

Here's an example app on shinylive.io demonstrating the behavior I observed:

• When multiple=True and selected=None, an empty selection is allowed, even if "" isn't in the choices.
• When multiple=False and selected=None, an empty selection is not allowed unless "" is in the choices.

[gadenbuie]

It still works, but you're encountering the issue described in #1384. In short, users can press delete to remove the item and then Tab or click away from the input. It's not very clear that that's possible, but you can enable the clear button plugin to improve the user experience.

[ME-researchgroup]

In shiny 0.9, I was able to have an initial 'empty state' for the input_selectize (e.g., for an optional parameter). Am I correct in that this no longer seems possible in shiny 0.10 and a user will have to clear it manually?

[gadenbuie]

For an initial empty state, I think you now need to include the empty selection in the initial choices. This snippet works for me

    ui.input_selectize(
        "example2",
        "Unexpected behavior",
        choices=["", "one", "two"],
        multiple=False,
        selected=None,
    ),

[selting]

Note that the proposed solution works only, if "" is the first option. That is, the following version does not work:

ui.input_selectize(
        "example2",
        "Unexpected behavior",
        choices=["one", "two", ""],  # <--- note the order of choices
        multiple=False,
        selected=None,
    ),