如何在html.div中输出值？

Question

我有一个打印随机值的函数。 当按下按钮

Start

时，该功能被“激活”。

            print("acquisition is on")
            print(random.random())

此时控制台中会打印随机值。但我想知道如何直接在html.Div中输出这个值。

以下是完整代码

from dash import Dash, html, dcc, Input, Output, ctx
import dash_bootstrap_components as dbc
import time
import threading
import random


app = Dash(
    __name__,
    external_stylesheets = [dbc.themes.SPACELAB, dbc.icons.FONT_AWESOME],
    title = 'MT',
    prevent_initial_callbacks = "initial_duplicate"
)



class Nanotec(threading.Thread):

    def __init__(self, *args, **kwargs):
        # When Main is excuted, this does :
        super(Nanotec, self).__init__(*args, **kwargs)
        self.__flag = threading.Event() # The flag used to pause the thread
        self.__flag.set() # Set to True
        self.__running = threading.Event() # Used to stop the thread identification
        self.__running.set() # Set running to True
        

    def run(self):
        while self.__running.isSet():
            self.__flag.wait() # return immediately when it is True, block until the internal flag is True when it is False
            print("acquisition is on")
            print(random.random())
            time.sleep(1)


    def pause(self):
        self.__flag.clear() # Set to False to block the thread
        print("pausing")

    def resume(self):
        self.__flag.set() # Set to True, let the thread stop blocking
        print("resuming")

    def stop(self):
        self.__flag.set() # Resume the thread from the suspended state, if it is already suspended
        self.__running.clear() # Set to False


@app.callback(Output('container', 'children'),
              Input('btn_start_nanotec', 'n_clicks'),
              Input('btn_pause_nanotec', 'n_clicks'),
              Input('btn_resume_nanotec', 'n_clicks')
              )
def display(btn_start_nanotec, btn_pause_nanotec, btn_resume_nanotec):
        button_id = ctx.triggered_id if not None else 'No clicks yet'
        if button_id == "btn_start_nanotec" :
            my_thread_nanotec.start()
        elif button_id == "btn_pause_nanotec" :
            my_thread_nanotec.pause()
        elif button_id == "btn_resume_nanotec" :
            my_thread_nanotec.resume()

my_thread_nanotec = Nanotec()

app.layout = html.Div([
    html.Button('Start', id='btn_start_nanotec'),
    html.Button('Pause', id='btn_pause_nanotec'),
    html.Button('Resume', id='btn_resume_nanotec'),
    html.Div(id='container'),
    html.Br(),

])

if __name__ == "__main__":
   app.run_server(debug = True)

Answer 1

我不太确定你想在这里对多线程类做什么。它应该每秒更新一次

html.Div

吗？单击按钮时文本是否应该更新？

但是由于问题是“如何赋值……”，这里有一个快速解释。我用一个简单的生成器替换了多线程类，以使事情变得更清晰。 您的回调应该返回要放入

html.Div

的值。所以这里的值是从生成器中获取的（当单击按钮时）并返回：

import random
from dash import Dash, html, dcc, Input, Output, ctx


app = Dash(__name__, title="MT", prevent_initial_callbacks="initial_duplicate")

def randoms():
    while True:
        yield random.random()


random_iter = randoms()


@app.callback(
    Output(component_id="container", component_property="children"),
    Input("btn_start_nanotec", "n_clicks"),
    Input("btn_pause_nanotec", "n_clicks"),
    Input("btn_resume_nanotec", "n_clicks"),
)
def display(*_):
    button_id = ctx.triggered_id
    if button_id == "btn_start_nanotec":
        result = next(random_iter)
    elif button_id == "btn_pause_nanotec":
        result = 'Pause?..'
    elif button_id == "btn_resume_nanotec":
        result = next(random_iter)
    return result


app.layout = html.Div(
    [
        html.Button("Start", id="btn_start_nanotec"),
        html.Button("Pause", id="btn_pause_nanotec"),
        html.Button("Resume", id="btn_resume_nanotec"),
        html.Div(id="container"),
        html.Br(),
    ]
)

if __name__ == "__main__":
    app.run_server(debug=True)

您可以将我的超级简单迭代器替换为其他任何东西（

threading.Thread

，

multiprocessing.Pool

，等等），但回调仍然必须从源获取值并返回它。

间隔

如果您需要定期更新输出（每秒一次），请查看Intervals。相同的基本原理是一样的（回调返回值），但它会为您处理定期更新。

使用 Websocket 消息更新输入

Websocket

组件似乎非常适合这个要求：数据由另一个进程/线程发送并（某种程度上）实时更新，甚至支持双向通信（暂停/恢复）。