Element callback update

[morningstarsabrina]

Hello,

Is it possible to add set_callback method to elements such as button so we can change or add the callback later ?

thanks

[morningstarsabrina]

can somebody help me to achieve this ?

[rodja]

Why would you like to do this? You can register a callback function to the button and then inside the function decide what to do. Why change the callback itself? Otherwise each element has a list ._event_listeners which you could manipulate...

[morningstarsabrina]

I want to do this because I want to use separated files design. defining element in one file and add callback in other files when I have logic functions.
could you show me an example about ._event_listeners

thanks

[rodja]

I see. You don't want to change the callback. You just want to add a callback. That can be achieved with the generic .on event registration. Here is a super small example:

b = ui.button('Click')
ui.button('Add callback', on_click=lambda: b.on('click', lambda: ui.notify('Clicked!')))

[morningstarsabrina]

yes I want to add call back.
I hope in future there will be a cleaner method to add callbacks, but currently this is more than enough.
I come from Qt framework when you can simply use methods such as 'connect' to add call back and 'disconnect' to stop listening. you can even add more than 1 callback.
thank you very much for your help !

[rodja]

With .on you can already add multiple callbacks to one element. But yes, removing/updating is not so easy right now. We will may implement something in the future. Thanks for sharing your requirement with us.

[morningstarsabrina]

thank you for accepting suggestions in a positive way !

[morningstarsabrina]

@rodja

so I'm trying the example you gave me

b = ui.button('Click')
ui.button('Add callback', on_click=lambda: b.on('click', lambda: ui.notify('Clicked!')))

I noticed now it create another button with text 'Add callback' that I have to click on it first to make b button work.
I'm doing something wrong ?
What I'm trying to do is to add a call back the 'b' button without creating another button

[rodja]

The second button was only meant for demonstration. Use it like this:

In your design file:

b = ui.button('Click')

In your business logic:

def some_on_click_handler():
    print('clicked')

b.on('click', some_on_click_handler)

[morningstarsabrina]

ok thanks.
by the way for me print() work only if I put print('clicked', flush = True) is this normal ? is there a better way without putting flush ?

[rodja]

Yes, flushing is required when using print. Most of the time we work with the Python logging module.

[morningstarsabrina]

thanks for the tip