[BUG] Adding new Pattern Matching components don't trigger their related callback

[chgiesse]

Describe your context

dash                 3.0.0rc3, 3.0.0rc2, 3.0.0rc1, 2.8.12

• not front end related

Describe the bug
Pattern matching callback that should be triggered as soon as a related component is present in the layout just fire the first time the page is loaded. New components that get add by the callback itself should trigger the callback again but those trigger don't happen.

MRE

# app.py
from dash import Dash, html, page_container, dcc, callback, MATCH, Input, Output
from pages.components import LacyContainer
import time

app = Dash(__name__, use_pages=True)

col_style = {
    "display": "flex",
    "flexDirection": "column",
    "gap": "2rem",
}

row_style = {
    "display": "flex", 
    "flexDirection": "row", 
    "gap": "4rem", 
    "margin": "2rem"
}

app.layout = html.Div(
    style=row_style,
    children=[
        html.Div(
            style=col_style,
            children=[
                dcc.Link("Page - 1", href="/page-1"),
                dcc.Link("Page - 2", href="/page-2"),
            ]
        ),
        html.Div(page_container),
    ],
)

@callback(
    Output(LacyContainer.ids.container(MATCH), "children"),
    Input(LacyContainer.ids.container(MATCH), "id")
)

def load_lacy(lacy_id):
    time.sleep(1.3)
    lacy_index = lacy_id.get('index')
    children = (
        html.Div(
            children=[
                html.Div(lacy_index),
                LacyContainer(dcc.Loading(display="show"), index=3),     
            ],
            style=col_style
        )
        if lacy_index < 4 else
        html.Div(
            lacy_index
        )
    )

    return children

if __name__ == "__main__":
    app.run(debug=True, port=3000)

# pages/page1.py
from dash import dcc, register_page
from .components import LacyContainer

register_page(__name__, path="/page-1")


def layout(**kwargs):
    return LacyContainer(dcc.Loading(display="show"), index=1)

# pages/page2.py
from dash import dcc, register_page
from .components import LacyContainer

register_page(__name__, path="/page-2")


def layout(**kwargs):
    return LacyContainer(dcc.Loading(display="show"), index=2)

# components.py
from dash import html


class LacyContainer(html.Div):
    class ids:
        container = lambda idx: {"index": idx, "type": "lacy-container"}

    def __init__(self, children, index, **kwargs):
        super().__init__(children, id=self.ids.container(index), **kwargs)

Expected behavior
The expected behaviour would be:

1. Page is loaded and contains multiple "lacy components" with a dict ID
2. lacy component trigger the callback
3. callback itself returns new "lacy components" which trigger the callback again up to the point, no more lacy component is present in the layout

Screenshots

The dots underitems should trigger the callback and should be replaced, but this never happens.

Thanks in advance and many thanks for your great work!

[T4rk1n]

dash 3.0.0rc3, 3.0.0rc2, 3.0.0rc1, 2.8.12

I think I've seen this bug reported before, can you confirm the bug is present in dash 2.x?

[chgiesse]

You are insane, thanks for this rapid response! Yes can confirm, at least for 2.18.2. If it helps, I can also check prev. versions! Best regards,
Christian

[T4rk1n]

You are insane, thanks for this rapid response! Yes can confirm, at least for 2.18.2. If it helps, I can also check prev. versions! Best regards, Christian

Thanks, just wanted to confirm it is not a regression in 3.0.0 RC.

[chgiesse]

Do you have an initial thought on why and where this behaviour appears? Would like to support here but I just started to go through the dash renderer since your big 3.0 changes.