How to avoid re-render after i've added and Item to the list?

Question

I have a functional component that needs to be updated.

export const VendorCategory = ({setShowProgress, user}) => {
    const classes = useStyles()
    const theme = useTheme()
    const listElements = []
    const [dummyCategory, setDummyCategory] = useState({
        "Test1": [
            "Subtest1", "Subtest2", "Subtest3"
        ],
        "Test2": [
            "Subtest1", "Subtest2", "Subtest3"
        ],
        "Test3": [
            "Subtest1", "Subtest2", "Subtest3"
        ]
    })


    useEffect(() => {
        return () => {
            console.log("re-rendered")
        }
    })
    const AddSubCategory = useCallback(() => {
        setShowProgress(true)
        const newAdd = dummyCategory['Test1']
        newAdd.push("SubTest4")
        setDummyCategory({...dummyCategory, "Test1": newAdd})
        setShowProgress(false)
    },[setShowProgress,setDummyCategory,dummyCategory])



    return (
        <div className={classes.root}>

            <h3 className={classes.title}>Vendor Category</h3>

            <Button
                className={classes.button}
                variant='contained'
                color="primary"
            >
                Add Category
            </Button>
            <div className={classes.categoryDiv}>
                {
                    Object.keys(dummyCategory).map((value, index) => {
                        return (
                            <List>
                            <Accordion key={uuid()} mt={2}>
                                <AccordionSummary
                                    expandIcon={<ExpandMoreIcon/>}
                                    aria-controls="panel1a-content"
                                    id="panel1a-header"
                                >
                                    <ListSubheader key={uuid()} className={classes.sublistHeader} component="div"
                                                   id="nested-list-subheader">
                                        {value}
                                    </ListSubheader>
                                </AccordionSummary>


                                <AccordionDetails className={classes.subCategoryList}>
                                    <Button
                                        className={classes.button}
                                        variant='contained'
                                        color="primary"
                                        onClick={AddSubCategory}
                                    >
                                        Add Sub-Category
                                    </Button>
                                    {dummyCategory[value].map((subvalue, index) => {
                                        return (
                                            <ListItem button key={subvalue}>
                                                <ListItemText inset primary={subvalue}/>
                                            </ListItem>
                                        )
                                    })}

                                </AccordionDetails>
                            </Accordion>
                            </List>)
                    })
                }

            </div>
        </div>
    )
}

const mapStateToProps = (state) => ({
    user: state.user
})

const mapDispatchToProps = {}

export default connect(mapStateToProps, mapDispatchToProps)(VendorCategory)

the problem is the accordion is re-rendered every time I add an item to it and then it collapses. how do I stop it from collapsing due to re-render?UseCallback hook also re-renders. how do i use React.Memo to avoid this? Or how do I use useEffect in such a case. Again, I need to add an item without the accordion collapsing. is it possible? Any help will be appreciated.

Answer 1

As per the comments, mapped React elements should be given unique, stable keys that persist throughout the lifespan of the element. When a key changes, as far as React is concerned then a new component has been mounted.

Functions called inline on an element or component like key={uuid()} or onClick={handleClick()} will be called on every render. In this case, calling uuid() inline was generating a new key for every render of the parent component, causing the mapped child components to be remounted.

Answer 2

React.memo avoids the re-render. In your Accordion function, try:

import {memo} from 'react';

const Accordion = (props) => {
    //your code
};

export default memo(Accordion);