Plotly-Dash：隐藏和取消隐藏下拉菜单

Question

I would like to launch my Dash with my dropdown hide and after selecting something on another dropdown unhide my first dropdown. Idk if you have any idea, maybe it's a mistake on my little script.

This is a little example:

import dash
from dash.dependencies import Input, Output
import dash_core_components as dcc
import dash_html_components as html

app = dash.Dash('example')

app.layout = html.Div([
    dcc.Dropdown(
        id = 'dropdown-to-show_or_hide-element',
        options=[
            {'label': 'Show element', 'value': 'on'},
            {'label': 'Hide element', 'value': 'off'}
        ],
        value = 'off'
    ),

    # Create Div to place a conditionally visible element inside
    html.Div([
        # Create element to hide/show, in this case an 'Input Component'
        dcc.Input(
        id = 'element-to-hide',
        placeholder = 'something',
        value = 'Can you see me?',
        )
    ], style= {'display': 'none'} # <-- This is the line that will be changed by the dropdown callback
    )
    ])

@app.callback(
   Output(component_id='element-to-hide', component_property='style'),
   [Input(component_id='dropdown-to-show_or_hide-element', component_property='value')])

def show_hide_element(visibility_state):
    if visibility_state == 'on':
        return {'display': 'block'}
    if visibility_state == 'off':
        return {'display': 'none'}

if __name__ == '__main__':
    app.server.run(debug=False, threaded=True)

Answer 1

By slightly changing your code (I changed the parameter that your function takes and using that same parameter in the if statement, this code seems to work). I also change the original style to block , which allows the element to be there, but only shown when on the show dropdown.

import dash
from dash.dependencies import Input, Output
import dash_core_components as dcc
import dash_html_components as html

app = dash.Dash('example')

app.layout = html.Div([
    dcc.Dropdown(
        id = 'dropdown-to-show_or_hide-element',
        options=[
            {'label': 'Show element', 'value': 'on'},
            {'label': 'Hide element', 'value': 'off'}
        ],
        value = 'off'
    ),

    # Create Div to place a conditionally visible element inside
    html.Div([
        # Create element to hide/show, in this case an 'Input Component'
        dcc.Input(
        id = 'element-to-hide',
        placeholder = 'something',
        value = 'Can you see me?',
        )
    ], style= {'display': 'block'} # <-- This is the line that will be changed by the dropdown callback
    )
    ])

@app.callback(
   Output(component_id='element-to-hide', component_property='style'),
   [Input(component_id='dropdown-to-show_or_hide-element', component_property='value')])

def show_hide_element(value):
    if value == 'on':
        return {'display': 'block'}
    if value == 'off':
        return {'display': 'none'}

if __name__ == '__main__':
    app.server.run(debug=False)