Update components via session_state

[coolkau]

Problem

IT seems that the overall code style is to provide a default value to the widget or component. Then, after the first run, the value can be updated via the relevant key in the session_state.

Ie. I update st.session_state["widget_key"] via a callback. Then the widget will show the updated value

This works with widgets. However, it is not clear how to achieve this with components. Components dont change the value, they will be out of sync with the session state.

I looked around none of the community components will upate; none of them is able to interact with other widgets via callbacks/ session_State. One widget solved this by having an explicit value parameter to update; this works but might not be the "streamlitty" way of doing things.

Solution

Provide a way to pull the new stession_state into the react state upon re-rendering. If this exists, provide documentation or tutorials for this, as I did not manage to get this to work and it seems nobody else did (At least I did not find any example for this).

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[willhuang1997]

Hi @coolkau ,

Is this the same as this issue? It does seem to be but can you confirm for me?

#3977

[coolkau]

Nope its not,
the other one is adressing the issue that custom components dont have a callback. (also a big wish but there is a simple hack in that issue :) )

Mine is pretty much a bug. Meaning if you use callbacks to update the session-state key, the custom component with that key does not update. At that point the app is essentially broken.

def callback():
     st.session_state["key"] = False

component(detault_value=True, key="key)

If the callback triggers, the component value does not update to False. This is true for all components I downloaded; I tried to play a bit to see if I can set the react_state to some prop, but did not see anything which looked like something useful.

You basically need to decide if you

• either want to add the ability to pass a new session_state into the react component (or create enbablement how to do this),
• or remove the key property from components -- and thus removing the ability to interact via callbacks / the session state.

(Unless I am missing something strikingly obvious, which might be the case as well)

[carolinedlu]

Hey @coolkau, is this essentially the same as #5634?

[coolkau]

Nope, also that one is different. Let me know if I should elaborate.

[willhuang1997]

@coolkau , so if I understand correctly, it seems you want to have custom components be able to update their session state value just like widgets and this currently doesn't work? Let me know if I understand it properly or where I am going wrong.

[coolkau]

No, let me try this again:
There are two states, the "backend one", the one from streamlit, the sessoin_state. And the frontend one, which is in the iFrame, in the React Component. Those should be in sync.

Normally you would have a 2 way connection beween the the central store (e.g. redux) and the widget.
In the case of streamlit you push a change in component state back to streamlit, which then triggers a rerun of the entire script.

In theory you dont need to push a change of the steamlit change to the componented state. You should get a new component after every change/rerun. However it seems that not the entire component is wiped when rerunning. This means the session state changes, but the component still has the state of the earlier run. I tried to find a way how to get updates from the steamlit state but did not find a way

[nicedouble]

+1 for this issue.Hope streamlit can publish v2 custom component api,so that can change custom component value by session state.