如何在短划线中插入多个下拉列表

Question

我正在尝试使用Plotly Dash，但我被这一块卡住了，我想动态添加用户定义数量的下拉列表。以下是我尝试过的：

# Import required libraries
import dash
import math
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output, State

# App Begins
app = dash.Dash(
__name__, meta_tags=[{"name": "viewport", "content": "width=device-width"}],
)
app.title = "Tool"
server = app.server
# Create global chart template
mapbox_access_token = "pk.eyJ1IjoicGxvdGx5bWFwYm94IiwiYSI6ImNrOWJqb2F4djBnMjEzbG50amg0dnJieG4ifQ.Zme1-Uzoi75IaFbieBDl3A"
layout = dict(
autosize=True,
automargin=True,
margin=dict(l=30, r=30, b=20, t=40),
hovermode="closest",
plot_bgcolor="#F9F9F9",
paper_bgcolor="#F9F9F9",
legend=dict(font=dict(size=10), orientation="h"),
title="Satellite Overview",
mapbox=dict(
accesstoken=mapbox_access_token,
style="light",
center=dict(lon=-78.05, lat=42.54),
zoom=7,
),
)
# Create app layout
app.layout = html.Div(
[
dcc.Store(id="aggregate_data"),
# empty Div to trigger javascript file for graph resizing
html.Div(id="output-clientside"),
html.Div(
[
html.Div(
[
html.Img(
src=app.get_asset_url("dash-logo.png"),
id="plotly-image",
style={
"height": "60px",
"width": "auto",
"margin-bottom": "25px",
},
)
],
className="one-third column",
),
html.Div(
[
html.Div(
[
html.H3(
"Dash Tool",
style={"margin-bottom": "0px"},
),
]
)
],
className="one-half column",
id="title",
),
],
id="header",
className="row flex-display",
style={"margin-bottom": "25px"},
),
html.Div(
[
html.Div(
[
html.P("Quantity 1:", className="control_label"),
dcc.Input(
id="quantity_1",
type="number",
placeholder=33.
),
html.P("Quantity 2:", className="control_label"),
dcc.Input(
id="quantity_2",
type="number",
placeholder=-115.
),
html.P("Number of Drop Downs:", className="control_label"),
dcc.Slider(
id="drop_downs",
min=2,
max=10,
value=2,
step=1.0,
className="dcc_control",
),
html.P("Load Inputs:", className="control_label"),
dcc.Checklist(
id='sources_flag',
options=[
{'label': 'Yes', 'value': 'Y'},
],
value=['Y'],
labelStyle={'display': 'inline-block'}
),
html.Div(id='source_dropdown_container', children=[]),
html.Div(id='source_dropdown_container_output'),
html.Div(id='source_file_container', children=[]),
html.Div(id='source_file_container_output'),
],
className="pretty_container four columns",
id="cross-filter-options",
),
],
className="row flex-display",
),
],
id="mainContainer",
style={"display": "flex", "flex-direction": "column"},
)

# Create callbacks
@app.callback(
[
Output(component_id='source_dropdown_container_output', component_property='children'),
],
[
Input(component_id='drop_downs', component_property='value'),
Input(component_id='sources_flag', component_property='value'),
]
)
def update_source_dropdowns(value, value_1):
"""Controls the number of drop-downs available to choose sources"""
if value_1 == 'Y':
children = []
for i in range(0, value):
new_dropdown = dcc.Dropdown(
id=f'''source_dropdown_{str(i)}''',
options=['GOOG', 'FB', 'TDOC', 'FANG']
)
children.append(new_dropdown)
print(children)
print(type(children))
return children

我一直遇到回调错误。下拉列表构造正确，所以我有点困惑为什么会调用那个错误。

dash.exceptions.InvalidCallbackReturnValue: The callback ..source_dropdown_container_output.children.. is a multi-output.
Expected the output type to be a list or tuple but got:
None. 

感谢任何指导或帮助。我所要做的就是根据用户输入在布局中添加动态数量的下拉列表。

Answer 1

回调中有三个错误

1. 只有一个返回，因此不要将输出定义为列表
2. 条件检查错误，应为if value_1 == ['Y']:
3. doc.Dropdown()选项参数需要定义dict的列表

# Create callbacks
@app.callback(
Output(component_id='source_dropdown_container_output', component_property='children'),
[
Input(component_id='drop_downs', component_property='value'),
Input(component_id='sources_flag', component_property='value'),
]
)
def update_source_dropdowns(value, value_1):
"""Controls the number of drop-downs available to choose sources"""
print("cb", value, value_1)
if value_1 == ['Y']:
children = []
for i in range(0, value):
new_dropdown = dcc.Dropdown(
id=f'''source_dropdown_{str(i)}''',
options=[{"label":v, "value":v } for v in ['GOOG', 'FB', 'TDOC', 'FANG']],
)
children.append(new_dropdown)
print(children)
print(type(children))
return children