在功能反应组件中无限重新渲染

Question

I am trying to set the state of a variable "workspace", but when I console log the data I get an infinite loop. I am calling the axios "get" function inside of useEffect(), and console logging outside of this loop, so I don't know what is triggering all the re-renders. I have not found an answer to my specific problem in this question . Here's my code:

function WorkspaceDynamic({ match }) {
  const [proposals, setProposals] = useState([{}]);
  useEffect(() => {
    getItems();
  });

  const getItems = async () => {
    const proposalsList = await axios.get(
      "http://localhost:5000/api/proposals"
    );
    setProposals(proposalsList.data);
  };

  const [workspace, setWorkspace] = useState({});
  function findWorkspace() {
    proposals.map((workspace) => {
      if (workspace._id === match.params.id) {
        setWorkspace(workspace);
      }
    });
  }

Does anyone see what might be causing the re-render? Thanks!

Answer 1

The effect hook runs every render cycle, and one without a dependency array will execute its callback every render cycle. If the effect callback updates state, ie proposals , then another render cycle is enqueued, thus creating render looping.

If you want to only run effect once when the component mounts then use an empty dependency array.

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

If you want it to only run at certain time, like if the match param updates, then include a dependency in the array.

useEffect(() => {
  getItems();
}, [match]);

Answer 2

your use of useEffect is not correct. if your dependency array is empty it gets called every time any state data changes.as a result your useEffect is called which causes setProposals then it again causes useEffect to run and so on

try this

useEffect(() => {
    getItems();
  } , []);   // an empty array means it will be called once only

Answer 3

I think it's the following: useEffect should have a second param [] to make sure it's executed only once. that is:

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

otherwise setProposal will modify the state which will trigger a re-render, which will call useEffect , which will make the async call, which will setProposal , ...