Can't Update state after fetch request-CodePudding

I'm trying to make an app where I fetch data from a Graphql API, and update state after fetching, but after the successful request I'm getting the data but I can't update state with that data. when I console log the response data it's showing the array with required data but when I update state and console log the state it's showing empty array.

I need to update the state to use it in the component, when i'm doing this it's throwing error that currList is undefined.

here are pictures of code and console.

export default function App() {
  const [search, setSeach] = useState("");
  const [currList, setCurrList] = useState([]);

  const fetchShips = async () => {
    const response = await request(gql`
      {
        ships {
          name
          home_port
          image
        }
      }
    `);
    console.log("request response", response.data);
    setCurrList(response.data);
    console.log("currlist:", currList);
  };

  useEffect(() => {
    fetchShips();
  }, [currList]);

  const Searchitems = (event) => {
    setSeach(event.target.value);
    setCurrList(
      currList.filter((item) => {
        return item.name.includes(search) || item.home_port.includes(search);
      })
    );
  };

  return (
    <div className="App">
      <div className="container">
        <header></header>
        <div className="body">
          <input
            type="text"
            id="search"
            value={search}
            onChange={Searchitems}
            className="input"
            placeholder="Search Ships"
          />
          <p>Total Count: {currList.length}</p>
          <div className="ships">
            {currList.map((item, index) => {
              return (
                <Ship
                  key={index}
                  name={item.name}
                  port={item.port}
                  img={item.image}
                />
              );
            })}
          </div>
        </div>
      </div>
    </div>
  );
}

CodePudding user response：

the State is Updated just not when the code is running that's why it logs that the state is an empty array, try to console.log it once again and you will see that there is something in the List.

CodePudding user response：

That's normal, everything is happening asynchronously. React will trigger a re-render once your currList is updated and you will get its new value. If you want to listen to this change, you have to use useEffect with currList as a dependency.

useEffect(() => {
    console.log("List is updated", currList);
}, [currList]);

CodePudding user response：

The function fetchShips has closure over the currList state variable that blongs to specific render call, so when you log it after calling setCurrList it shows you the previous state not the updated state, you can log it in the useEffect to see the changes.

CodePudding user response：

I had the same problem once. I couldn't find efficient solution but my solution saved me anyway.

I used useRef instead of useState. Try this:

  const currList = useRef([]);

useEffect=(()=>{
const fetchShips = async () => {
    const response = await request(gql`
      {
        ships {
          name
          home_port
          image
        }
      }
    `);
    console.log("request response", response.data);
     // setCurrList(response.data);
if(response)
    currlist.current = response.data

    console.log("currlist:", currList);
  };
fetchShips()
// Also as far as I know ,you should use useEffect like this
},[])
//... codes

return(
//... codes
 currList.current.map(...

)
//... codes

Before using useRef, try to define your fetchShips function inside useEffect so maybe you don't need my solution.

Why is not efficient my solution for your case? When you want to update your currList data, useRef does not trigger re-render. Even if your data updated, you cannot see it on your screen. So setCurrList(currList.current) can save you but as I said earlier it may not efficient way.