[Callback] Programmatically add callback

Dash Python
1

Hi,
I’ve built a Dash application, with lots of Dropdowns everywhere, some of them with multiple values.
I’ve been asked to add a ‘Select all’ button on all multi-select dropdowns.
To stay DRY, I’ve build a wrapper for dropdowns, and I would need to update it to add the ‘Select all’ button and the corresponding callback there, something like below:

def create_dropdown(*args, **kwargs):
    dropdown = dcc.Dropdown(*args, **kwargs)
    if kwargs.get('multi', False):
        @app.callback(...)
        def update_value(n_clicks):
             return kwargs.get(options, [])

        return html.Div([dropdown, html.Button('Select all', id=...)])
    return dropdown

Unfortunately, this way, the callback is not applied, though the button is rendered.
Has anyone any clue how I can achieve the intended behavior ?
Thanks

2

This sounds like a good opportunity for the brand new pattern matching callbacks: Pattern-Matching Callbacks | Dash for Python Documentation | Plotly

3

you’ll have to make sure that all of these callbacks are registered before run_server is called. callbacks can’t be registered dynamically. if you are adding these components dynamically, then pattern matching callbacks is the way to go.

4

I don’t seem to be able to figure out how to use a different list of options (+ default value and everything else) for each different drop down, using a pattern-matching callback.

Also, pattern-matching callbacks are applied once to all items (the function takes the list of all Inputs matching the pattern as arguments), while my Dropdowns are totally independent from one another.

5

The solution I use is indeed pattern-matching callbacks, using the MATCH keyword (I was focused on the ALL keyword).

An other one would be (in my case) to write a function creating both the callback and the layout, and to make sure to call this function only once, when creating the layout. That’s a bit more complex and quite ugly.