useState is not managing state in react native

Question

I'm fetching data from Api, and then updating my state, but state is just holding last element of array, I'm using spread operator.

const Index=()=>{
    const [data, setData] = useState([]); //append new messages in this data
    const [keys, setKeys] = useState([]); //users ids will be stored in this state
    const fetchNewData = async allKeys => {
         for(let i=0;i<allKeys.length;i++){
             let newUserData=//fetching data from somewhere
             setData([...data,newUserData]) //now this fucntion is not setting state properly 
         }
    }
    //this useEffect is dependent on **teacher** state
    useEffect(() => {
       let tempKeys = Context.teacher.map(item => item.id);
       fetchNewData(tempKeys);
       setKeys(tempKeys);
    }, [Context.teacher])
    //this useEffect is dependent on **data** state
    useEffect(() => {
       console.log('data has been set: ', data); //just single user is logged everytime
    }, [data]);
    return **jsx**
}
export default Index;

What do you mean by `not setting properly` and try to print the `newUseData` if it's working? — Rohit Aggarwal, Jun 20 '22 at 13:19
@RohitAggarwal yes, I printed newUserData which is totally fine, the issue arises when I set "data" state using "setData()", it is not copying previous data, it is just setting newUserData while previous data is losing... — Faizan Muhammad, Jun 20 '22 at 14:08

score 0 · Answer 1 · answered Jun 20 '22 at 14:51

0

updating array(state) like this works for me:

setState(oldValue=>[...oldValue,newValue])

answered Jun 20 '22 at 14:51

Faizan Muhammad

73
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useState is not managing state in react native

1 Answers1