Something went wrong when running the Event example

[v479038280]

Every time I run the Event example I got this error in the terminal .The application is running smoothly except for this.

NiceGUI ready to go on http://localhost:8080, http://169.254.254.33:8080, http://172.31.0.1:8080, and http://192.168.1.14:8080
Request is not set
Traceback (most recent call last):
  File "D:\Program Files\Python3114\Lib\site-packages\nicegui\background_tasks.py", line 93, in _handle_exceptions
    task.result()
  File "D:\Program Files\Python3114\Lib\site-packages\nicegui\app\app.py", line 100, in await_func
    await func
  File "D:\Program Files\Python3114\Lib\site-packages\nicegui\event.py", line 89, in register_disconnect
    await client.connected()
  File "D:\Program Files\Python3114\Lib\site-packages\nicegui\client.py", line 204, in connected
    purpose = (self.request.headers.get('Sec-Purpose') or self.request.headers.get('Purpose') or '').lower()      
               ^^^^^^^^^^^^
  File "D:\Program Files\Python3114\Lib\site-packages\nicegui\client.py", line 111, in request
    raise RuntimeError('Request is not set')
RuntimeError: Request is not set

Here is the example code

from nicegui import Event, ui

click = Event()
click.subscribe(lambda: ui.notify('clicked'))

ui.button('Click me', on_click=click.emit)

ui.run()

Additionally, this section of code actually has the same function as the one below. I wonder what greater purpose this implementation method serves.

from nicegui import  ui

ui.button('Click me', on_click=lambda: ui.notify('clicked'))

ui.run()

[python-and-novella]

what do you want?
It looks like signal of Qt, Do you know it?

[python-and-novella]

You can do as auto-index page before nicegui 3.0.0 by using Event:

from nicegui import ui,Event

signal_obj = Event()
shared_value = ''
def update_shared_value(x):
    global shared_value
    shared_value=x

def index():
    # 订阅信号，更新全局变量，以便于新打开的页面自动使用该值作为初始值
    signal_obj.subscribe(update_shared_value)
    input = ui.input(value=shared_value)
    # 订阅信号
    signal_obj.subscribe(lambda x:input.set_value(x))
    # 发射信号
    input.on_value_change(lambda :signal_obj.emit(input.value))

ui.run(root=index,port=80)

[v479038280]

那个Request is not set，你们没有报吗，我知道Qt，但不知道跟报这个存在什么有什么关系，我没使用Qt

[evnchn]

没报错啊，报了不会看不到……

Translate: he's saying that this is not related to Qt since he want to focus on how there is RuntimeError: Request is not set. I'm saying that we don't see this error, and we wouldn't have missed it when releasing 3.0.3 and #5221

[evnchn]

@v479038280 我知道了，你这个问题在 #5221 第2点修复了。因为你不在@ui.page里面配置UI，所以NiceGUI会以一个「脚本模式」启动，那本来Event的设计没考虑周到，现在有core.is_script_mode_preflight侦测并处理

Translate: I got it. The error is fixed in #5221 point 2, where since UI is no configured inside @ui.page so NiceGUI will run in "script mode". Event didn't fully consider this before. Now we got core.is_script_mode_preflight to cover this case.

[falkoschindler]

Thanks for bringing this up, @v479038280!

I agree that this demo is a bit too minimal. And we missed to try the code in isolation: Apparently it doesn't work in script mode (without page functions).

A better example might be something like this:

data_updated = Event()

@ui.page('/')
def page():
    data_updated.subscribe(lambda: ui.notify('Data has been updated'))

@ui.page('/data')
def data_page():
    ui.button('Update data', on_click=data_updated.emit)

There is a global event data_updated which the index page subscribes to. When the event is emitted, e.g. by clicking the button on another page, a notification is shown.

[python-and-novella]

I think it is a better example of bringing "auto-index" back:

from nicegui import Event, ui

click = Event()

def index():
    click.subscribe(lambda: ui.notify('clicked'))
    ui.button('Click me', on_click=click.emit)

ui.run(root=index)

[python-and-novella]

Without Event, the notify is only showen in current page, not all pages.

[python-and-novella]

BTW, the Event instance only works as expected when it was created in global scope and it was subscribed in page's scope or root function's scope.

[falkoschindler]

I just created PR #5221 to improve the demos.

[evnchn]

And it has been merged. See it in 3.1 I think. If there are any more unclear stuff please be sure to voice out and maybe even PR if you see necessary.

[falkoschindler]

@evnchn We even decided to sneak in another patch release 3.0.3: https://github.com/zauberzeug/nicegui/milestone/149

[v479038280]

from nicegui import Event, ui

click = Event()
click.execute(lambda: ui.notify('clicked'))

ui.button('Click me', on_click=click.emit)

ui.run()

If execute is a more accurate name?
I always think of subscribing to a server which publishes messages.
button.subscribe(some event)

[python-and-novella]

@v479038280 The Event of NiceGUI looks like signal of Qt. You create a Event instance in global scope ( but not in script mode), subscrib it in page scope. The subscribing is similar to Qt's slot. The calling or emittig of NiceGUI is similar to Qt signal's emitting.
So, I ask do you know Qt.
For Qt, you can binding one more slot to a signal, it is the same to NiceGUI. So, subscribe is a accurate name.