[BUG] A callback gets triggered without a corresponding event

[sergiykhan]

Software

dash                      2.8.1
dash-bootstrap-components 1.3.1
dash-core-components      2.0.0
dash-html-components      2.0.0
dash-table                5.0.0

Describe the bug

The value of the dropdown menu gets reset by a callback function that is only supposed to be triggered by an independent button in the interface. As you can see from the video recording below, typing in the drop-down menu triggers the button pressed event. There is no apparent connection between the two.

The Callback Graph is also recorded in the video below, showing the callback is called while no button is pressed.

Expected behavior

The callback on_button (see code below) should only be triggered when the button is actually pressed.

Console output

Button pressed 0 None
Button pressed 0 None
Button pressed 0 None
Button pressed 0 None
Button pressed 0 None

Video

screen-capture.mp4

Sample code

from dash import Dash, dcc, html, dcc, Input, Output, ctx
from dash.exceptions import PreventUpdate

options = [
    {"label": "aa1", "value": "aa1"},
    {"label": "aa2", "value": "aa2"},
    {"label": "aa3", "value": "aa3"},
    {"label": "best value", "value": "bb1"},
    {"label": "better value", "value": "bb2"},
    {"label": "bye", "value": "bb3"},
]

app = Dash(__name__)
app.layout = html.Div([
    html.Div([
        "Single dynamic Dropdown",
        dcc.Dropdown(id="my-dynamic-dropdown")
    ], style={'width': 200, 'marginLeft': 20, 'marginTop': 20}),
    html.Button(
        'Reset',
        id='button',
        n_clicks=0,
    ),
])


@app.callback(
    Output("my-dynamic-dropdown", "options"),
    Input("my-dynamic-dropdown", "search_value")
)
def update_options(search_value):
    if not search_value:
        raise PreventUpdate
    return [o for o in options if search_value in o["label"]]


@app.callback(
    Output('my-dynamic-dropdown', 'value'),
    Input('button', 'n_clicks'),
)
def on_button(n_clicks):
    print('Button pressed', n_clicks, ctx.triggered_id)
    return None


if __name__ == "__main__":
    app.run_server(debug=True, port=5000)

[sergiykhan]

I think it's likely a duplicate of issue #2428

[T4rk1n]

I think it's likely a duplicate of issue #2428

Yes duplicate of #2428, fixed in 2.9

[sergiykhan]

I have just tested it in Dash 2.9.2, and the bug is still present. It appeared in Dash 2.7.1. Downgrading to 2.7.0 resolves the issue.

[sergiykhan]

@T4rk1n should I create a new issue or you can re-open this one (or #2428)?

[T4rk1n]

@sergiykhan No, seems like I fixed the inputs but Output behave strangely when callbacks share the same dropdown/checklist as Output.

#2487 is still open and contains some more info, so maybe add a link to this example.