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08: Signal trigger

Same setup as Example 07, but the consumer doesn't care about the payload. It just reacts to the edge. Demonstrates SignalTrigger (no-payload consumer) paired with a producer that returns {}.

The script​

from dash import html
from dash_extensions.enrich import Output, Trigger
from weaverlet.base import SignalOutput, SignalTrigger, WeaverletComponent, WeaverletApp, Identifier
from weaverlet.components import SignalComponent


class SignalTriggerComponent(WeaverletComponent):

    trigger_button_id = Identifier()
    label_p_id = Identifier()

    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.signal_component = SignalComponent()

    def get_layout(self):
        return html.Div(
            [
                self.signal_component(),  # child component
                html.Button('Click to trigger signal',
                            id=self.trigger_button_id),
                html.P(id=self.label_p_id)
            ]
        )

    def register_callbacks(self, app):

        @app.callback(
            SignalOutput(self.signal_component),
            Trigger(self.trigger_button_id, 'n_clicks')
        )
        def button_click():
            return {}

        @app.callback(
            Output(self.label_p_id, 'children'),
            SignalTrigger(self.signal_component)
        )
        def label_update():
            return 'Signal triggered!'


signal_trigger_component = SignalTriggerComponent()

wapp = WeaverletApp(root_component=signal_trigger_component)
wapp.app.run(port=8089)

Expected output​

  • The page shows a button and an empty paragraph.
  • Each click updates the paragraph to "Signal triggered!"

Notes​

  • The producer still returns a dict ({}); Dash callbacks must return something. Use empty dict when there's no meaningful payload.
  • SignalTrigger(sig) is the no-payload consumer adapter. The callback signature is def consume(): (no argument).
  • Don't confuse Trigger (from dash_extensions.enrich, turns any Dash prop into a no-payload input) with SignalTrigger (from weaverlet, turns a signal into a no-payload input). They're different adapters for different sources.
  • This pattern is good for "something happened, refresh that view". Modal open, toast show, data reload.

Try it locally​

pip install weaverlet
python signal_trigger_app.py

See also​