反应表，表结果中的 useState 钩子到默认值，尽管之前已设置

Question

I am using react-table to display fetched data within a table. You also have different buttons within that table to interact with the data such as deleting an entry, or updating its data (toggle button to approve a submitted row).

The data is being fetched in an initial useEffect(() => fetchBars(), []) and then being passed to useTable by passing it through useMemo as suggested in the react-table documentation. Now I can click on the previously mentioned buttons within the table to delete an entry but when I try to access the data ( bars ) that has been set within fetchBars() it returns the default state used by useState() which is an empty array []. What detail am I missing? I want to use the bars state in order to filter deleted rows for example and thus make the table reactive, without having to re-fetch on every update.

When calling console.log(bars) within updateMyData() it displays the fetched data correctly, however calling console.log(bars) within handleApprovedUpdate() yields to the empty array, why so? Do I need to pass the handleApprovedUpdate() into the cell as well as the useTable hook as well?

const EditableCell = ({
    value: initialValue,
    row: { index },
    column: { id },
    row: row,
    updateMyData, // This is a custom function that we supplied to our table instance
  }: CellValues) => {
    const [value, setValue] = useState(initialValue)
  
    const onChange = (e: any) => {
      setValue(e.target.value)
    }
 
    const onBlur = () => {
      updateMyData(index, id, value)
    }
  
    useEffect(() => {
      setValue(initialValue)
    }, [initialValue])
  
    return <EditableInput value={value} onChange={onChange} onBlur={onBlur} />
}

const Dashboard: FC<IProps> = (props) => {
    const [bars, setBars] = useState<Bar[]>([])
    const [loading, setLoading] = useState(false)

    const COLUMNS: any = [
        {
            Header: () => null,
            id: 'approver',
            disableSortBy: true,
            Cell: (props :any) => {
                return (
                    <input
                        id="approved"
                        name="approved"
                        type="checkbox"
                        checked={props.cell.row.original.is_approved}
                        onChange={() => handleApprovedUpdate(props.cell.row.original.id)}
                    />
                )
            }
        }
    ];

    const defaultColumn = React.useMemo(
      () => ({
        Filter: DefaultColumnFilter,
        Cell: EditableCell,
      }), [])

    const updateMyData = (rowIndex: any, columnId: any, value: any) => {
        let barUpdate;
        setBars(old =>
            old.map((row, index) => {
                if (index === rowIndex) {
                    barUpdate = {
                        ...old[rowIndex],
                        [columnId]: value,
                    }
                    return barUpdate;
                }
                return row
            })
        )
        if(barUpdate) updateBar(barUpdate)
    }

    const columns = useMemo(() => COLUMNS, []);
    const data = useMemo(() => bars, [bars]);
    const tableInstance = useTable({
        columns: columns,
        data: data,
        initialState: {

        },
        defaultColumn,
        updateMyData
    }, useFilters, useSortBy, useExpanded );

    const fetchBars = () => {
         axios
            .get("/api/allbars",
                {
                    headers: {
                        Authorization: "Bearer " + localStorage.getItem("token")
                    }
                }, )
            .then(response => {
                setBars(response.data)
            })
            .catch(() => {
            });
    };

    useEffect(() => {
        fetchBars()
    }, []);

    const handleApprovedUpdate = (barId: number): void => {
        const approvedUrl = `/api/bar/approved?id=${barId}`
        setLoading(true)
        axios
            .put(
                approvedUrl, {},
                {
                    headers: {Authorization: "Bearer " + localStorage.getItem("token")}
                }
            )
            .then(() => {
                const updatedBar: Bar | undefined = bars.find(bar => bar.id === barId);
                if(updatedBar == null) {
                    setLoading(false)
                    return;
                }

                updatedBar.is_approved = !updatedBar?.is_approved
                setBars(bars.map(bar => (bar.id === barId ? updatedBar : bar)))
                setLoading(false)
            })
            .catch((error) => {
                setLoading(false)
                renderToast(error.response.request.responseText);
            });
    };

    const renderTable = () => {
        const {
            getTableProps,
            getTableBodyProps,
            headerGroups,
            rows, 
            prepareRow
        } = tableInstance;

        return(
            <table {...getTableProps()}>
                <thead>
                    {headerGroups.map(headerGroup => (
                        <tr {...headerGroup.getHeaderGroupProps()}>
                            {headerGroup.headers.map(column => (
                                <th {...column.getHeaderProps()}>
                                    <span {...column.getSortByToggleProps()}>
                                        {column.render('Header')}
                                    </span>{' '}
                                    <span>
                                        {column.isSorted ? column.isSortedDesc ? ' ▼' : ' ▲' : ''}
                                    </span>
                                    <div>{column.canFilter ? column.render('Filter') : <Spacer/>}</div>
                                </th>
                            ))}
                        </tr>
                    ))}
                </thead>
                <tbody {...getTableBodyProps()}>
                    {rows.map(row => {
                        prepareRow(row)
                        const rowProps = {...row.getRowProps()}
                        delete rowProps.role;
                        return (
                            <React.Fragment {...rowProps}>
                                <tr {...row.getRowProps()}>
                                    {row.cells.map(cell => {
                                        return (
                                            <td {...cell.getCellProps()}>{cell.render('Cell')}</td>
                                        )
                                    })}
                                </tr>
                                {row.isExpanded ? renderRowSubComponent({row}): null}
                            </React.Fragment>
                        )})
                    }
                </tbody>
            </table>
        )
    }
}

export default Dashboard;

Answer 1

You're seeing stale values within handleApprovedUpdate because it's capturing bars the first time the component is rendered, then never being updated since you're using it inside COLUMNS , which is wrapped with a useMemo with an empty dependencies array.

This is difficult to visualize in your example because it's filtered through a few layers of indirection, so here's a contrived example:

function MyComponent() {
  const [bars, setBars] = useState([]);

  const logBars = () => {
    console.log(bars);
  };

  const memoizedLogBars = useMemo(() => logBars, []);

  useEffect(() => {
    setBars([1, 2, 3]);
  }, []);

  return (
    <button onClick={memoizedLogBars}>
      Click me!
    </button>
  );
}

Clicking the button will always log [] , even though bars is immediately updated inside the useEffect to [1, 2, 3] . When you memoize logBars with useMemo and an empty dependencies array, you're telling React "use the value of bars you can currently see, it will never change (I promise)".

You can resolve this by adding bars to the dependency array for useMemo .

const memoizedLogBars = useMemo(() => logBars, [bars]);

Now, clicking the button should correctly log the most recent value of bars .

In your component, you should be able to resolve your issue by changing columns to

const columns = useMemo(() => COLUMNS, [bars]);

You can read more about stale values in hooks here . You may also want to consider adding eslint-plugin-react-hooks to your project setup so you can identify issues like this automatically.