Object 可能是“空”：TypeScript，React useRef & Formik innerRef

Question

In my React/TypeScript app that uses Formik, I am getting the error

Object is possibly 'null'.  TS2531

    125 |             <Modal.Footer>
  > 126 |                 <Button variant="primary" type="submit" form="nicknameForm" disabled={!(formRef.current.isValid && formRef.current.dirty)}>Apply</Button>
        |                                                                                            ^
    127 |             </Modal.Footer>
    128 |         </Modal>
    129 |     )

Tried changing formRef.current.isValid to formRef..current.isValid and formRef.current.dirty to formRef..current.dirty but the error persists.

Why is this so, and how can we fix this error? Thank you!

import React, { useState, useEffect, useRef } from 'react';
import { Button, Modal, Form } from 'react-bootstrap';
import { Formik } from 'formik';

interface IModal {
    show: boolean;
    handleClose: () => void;
}

export function NicknameModal({show, handleClose}: IModal) {

    const formRef = useRef(null);

    return (
        <Modal show={show} onHide={handleClose}>
            <Modal.Header closeButton>
                <Modal.Title>My Title</Modal.Title>
            </Modal.Header>
            <Modal.Body>
                <Formik
                    initialValues={{
                        nickname: '',
                    }}
                    innerRef={formRef}
                    onSubmit={(
                        values,
                        { setSubmitting }
                    ) => {
                        setSubmitting(true);
                        handleClose();
                        setSubmitting(false);
                    }}
                >
                    {({values, errors, touched, handleChange, handleBlur, handleSubmit, isSubmitting, setFieldValue }) => (
                        <Form id="nicknameForm" onSubmit={handleSubmit}>
                            <Form.Group controlId="formNickname">
                                <Form.Label>Nickname</Form.Label>
                                <Form.Control type="text" name="nickname" onChange={handleChange} onBlur={handleBlur} value={values.nickname} />
                            </Form.Group>
                        </Form>  
                    )}
                </Formik>
            </Modal.Body>
            <Modal.Footer>
                <Button variant="primary" type="submit" 
                 disabled={!(formRef.current.isValid && formRef.current.dirty)}
                 form="nicknameForm">Apply</Button>
            </Modal.Footer>
        </Modal>
    )
}

---

UPDATE:

If const formRef = useRef(null); is changed to const formRef = useRef(); , we now encounter a different error:

Type 'MutableRefObject<undefined>' is not assignable to type '((instance: FormikProps<{ nickname: string; }> | null) => void) & MutableRefObject<undefined>'.
  Type 'MutableRefObject<undefined>' is not assignable to type '(instance: FormikProps<{ nickname: string; }> | null) => void'.
    Type 'MutableRefObject<undefined>' provides no match for the signature '(instance: FormikProps<{ nickname: string; }> | null): void'.  TS2322

    71 |                         nickName: '',
    72 |                     }}
  > 73 |                     innerRef={formRef}
       |                     ^
    74 |                     onSubmit={(
    75 |                         values: Values,
    76 |                         { setSubmitting }: FormikHelpers<Values>

Answer 1

You need to set type for useRef, where FormValues is your form values

type FormValues = {};
useRef<FormikProps<FormValues>>(null);

https://github.com/formium/formik/issues/2600#issuecomment-693479057

Answer 2

Try with:

import { FormikProps } from "formik";

const formRef = useRef<FormikProps<any>>(null);