I am trying to read outside of the form the state saved in Redux and I got the same warning :

Related issue: #828

Is there a workaround or am I stuck with it?

@erikras Please any help on this? While the changes you published to #751 seem to work, I don't think it covers setting state inside the onChange function in a FormSpy.

Thanks.

The issue still persists with react-final-form@6.5.1 and final-form@4.20.1 with react version 16.13.1. Here's what I've found after digging through the (compiled) library source:

1. useField() is invoked internally by the react-final-form library from within the Field component.
2. It registers the field from within the lazy initializer function of a useState() hook. This parametrizes the internal register() function with a true second argument which is the silent flag. All is fine at this point.
3. However, despite the silent setting, final-form goes into a validation loop. I see in the stack trace that it invokes runValidation() which in turn leads to notifyFieldListeners() and then to notifySubscribers() on each field. This actually brings the code path back to react-final-form, into the useEffect() call inside of which the field is registered again but this time without the silent flag.
4. The actual culprit is:

   React.useEffect(function () {
     return register(function (state) {
       if (firstRender.current) {
         firstRender.current = false;
       } else {
         setState(state);
       }
     }, false);
   }

I think the following happens: from the aspect of one particular field, registration indeed happens properly (first with the silent and then without the silent flag) but other fields could have completed this cycle already. So, when a field gets initialized it runs into the validation loop, causing the setState() call to take place inside other fields, thereby violating the rule.

I have no suggestion at this point as to how it could be solved though.

Does someone already have a solution or workaround for that problem?

In my case this error was caused by a mutator, which was called on every FormSpy render.

I've solved this problem by wrapping the mutator call inside a useLayoutEffect and now everything works like before.

Does anyone have an example solution to this?

Hi all, I have been battling this issue while migrating from Redux-Form to React-Final-Form. Redux-Form has isDirty() in its API so I could easily get the state of a Form and use it in another (external) component. The only similar thing I can find for Final Form is FormSpy ( if not please let me know! ). In the end I had to give up and push the "dirty" flag into redux (in effect, rolling my own isDirty() for final-form) : which is when I bumped into the issue you are talking about here.

So far the only way I can get rid of the Warning is by wrapping the redux dispatch call in a cheeky setTimeout(,0). Hacky, stochastic, but it is working at least. Defo not a solution long term but thought I'd share :)

   // passed to FormSpy's onChange
   onChange = ({dirty}) => {
    // dodgy workaround to avoid Warning :P
    setTimeout(()=>this.props.dispatch( formActions.changed({dirty}) ) ,0)
  }

I am experiencing the same issue in our project.
I can help with investigation and report error details if needed.

@ThaNarie I hope you get rid of the error when you write it like this. this is how i solved it
<FormSpy
subscription={{ values: true,modified: true, }}
onChange={change => {
// fired during rendering, calling a useState setter fails
if(Object.keys(state.modified).length > 0){
setValues(change.values);}
}}
/>

In my case this error was caused by a mutator, which was called on every FormSpy render.

I've solved this problem by wrapping the mutator call inside a useLayoutEffect and now everything works like before.

Could you please give an example?

Seems like one of the solutions can be creating your own Spy component in such a case, e.g. simple implementation could look like this:

import { VFC, useEffect } from 'react'
import { useFormState } from 'react-final-form'

type Props = {
  onChange: (props: any) => void
}

const component: VFC<Props> = ({ onChange }) => {
  const state = useFormState()

  useEffect(() => {
    onChange(state)
  })

  return null
}

export default component

Little react hook: don't have a real onChange handler until after the first render is called.

function useAfterFirstRender(func) {
  const [retFunc, setFunct] = useState(() => ()=>{});
  useLayoutEffect(() => {
    setFunct(() => func);
  }, []);
  return retFunc;
}

Hi guys,
Is there any fix for this issue on the horizon? We are experiencing the same error; Although, our stack involves slightly more moving parts so it is difficult to diagnose correctly where the issue arises:
react-final-form: ˆ6.5.7
react-final-form-arrays: ˆ3.1.3
@dnd-kit/sortable: 7.0.0
Also various ui component libraries.

As far as I understood, the issue is caused by final-form setting state while rerendering?
Are there any news from the lib maintainer?

Please see #985 (comment)

Please see #985 (comment)

That is a different issue

wrapping the callback in requestAnimationFrame solved the problem for me

<FormSpy
    subscription={{ values: true }}
    onChange={(state) => {
        requestAnimationFrame(() => {
             // your callback body
        });
    }}
/>

For me, creating a new component that only fires the event if the page has rendered did the job:

import { useEffect, useRef } from "react";
import { FormSpy } from "react-final-form";

export const FormSpyWhenReady = ({
  subscription,
  onChange,
}: {
  subscription: { values: boolean };
  onChange: () => void;
}) => {
  const readyRef = useRef(false);
  useEffect(() => {
    readyRef.current = true;
  }, []);

  return (
    <FormSpy
      subscription={subscription}
      onChange={() => {
        if (readyRef.current) {
          onChange();
        }
      }}
    />
  );
};