Question

我通过react钩子设置了上下文。初始状态如下：

const initialState = {
    allTasks: [],
    tasksToAuth: [],
    pendingTasks: [],
    completedTasks: [],
    users: [],
    headers: headers,
    categories: categories
};

尝试通过api设置前五个属性时，会导致错误“无法对已卸载的组件执行React状态更新。这是空操作，但表示您的应用程序内存泄漏。要修复，请取消使用useEffect清理功能中的所有订阅和异步任务。“

我调用api的代码位于useEffect挂钩中。

React.useEffect(() => {
    async function getItems() {
        try {
            await actions.setAllTasks();
            await actions.setUsers();
            await actions.setUserPendingTasks();
            await actions.setTasksToAuth();
            await actions.setUserCompletedTasks();
        } catch (e) {
            alert("Error hit ", e);
            console.log(e);
        }
    }

    getItems();
}, [actions]);

我的操作和中间件/减速器如下：

Actions.js

setAllTasks: tasks => dispatch({ type: "admin.set.all.tasks", payload: tasks }),

setTasksToAuth: tasks => dispatch({ type: "admin.set.submitted", payload: tasks }),

setUserPendingTasks: tasks => dispatch({ type: "admin.set.pending", payload: tasks }),

setUserCompletedTasks: tasks => dispatch({ type: "admin.set.completed", payload: tasks }),

setUsers: tasks => dispatch({ type: "admin.set.users", payload: tasks }),

Middleware.js

switch (action.type) {
    case "admin.set.all.tasks":
        axios
            .get("http://localhost:3001/api/admin/tasks")
            .then(res => {
                console.log(res);
                dispatch({ type: action.type, payload: res.data.data });
            })
            .catch(e => console.log(e));
        break;

    case "admin.set.pending":
        axios
            .get("http://localhost:3001/api/admin/tasks/pending")
            .then(res => {
                console.log(res.data.data);
                dispatch({ type: action.type, payload: res.data.data });
            })
            .catch(e => console.log(e));
        break;

    case "admin.set.submitted":
        axios
            .get("http://localhost:3001/api/admin/tasks/submitted")
            .then(res => {
                console.log(res.data.data);
                dispatch({ type: action.type, payload: res.data.data });
            })
            .catch(e => console.log(e));
        break;

    case "admin.set.completed":
        axios
            .get("http://localhost:3001/api/admin/tasks/completed")
            .then(res => {
                console.log(res.data.data);
                dispatch({ type: action.type, payload: res.data.data });
            })
            .catch(e => console.log(e));
        break;

    case "admin.set.users":
        axios
            .get("http://localhost:3001/api/admin/users/")
            .then(res => {
                console.log(res);
                dispatch({ type: action.type, payload: res.data.data });
            })
            .catch(e => console.log(e));
        break;

最后，是reducer.js

case "admin.set.all.tasks":
    console.log("admin.set.all.tasks");
    return { ...state, allTasks: action.payload };

case "admin.set.pending":
    console.log("admin.set.pending");
    return mapPendingTasks(state, action.payload);

case "admin.set.submitted":
    console.log("admin.set.submitted");
    return mapSubmittedTasks(state, action.payload);

case "admin.set.completed":
    console.log("admin.set.completed");
    return mapCompletedTasks(state, action.payload);

case "admin.set.users":
    console.log("admin.set.users");
    return { ...state, users: action.payload };

这里似乎发生了错误-“ TypeError：无法设置未定义或空引用的属性“ uin””

据我所知，首先未正确设置allTasks的状态才能在下面首先创建任务对象？

reducer.js中返回的函数的示例是：

function mapCompletedTasks(state, payload) {
    let tasks = [];
    payload.forEach(element => {
        let task = state.allTasks.filter(e => e.id === element.task_id)[0];
        task.uin = element.uin;
        task.status = element.status;
        task.due_by = element.due_by;
        task.submitted_on = element.submitted_on;
        task.completed_on = element.completed_on;
        tasks.push(task);
    });
    return { ...state, completedTasks: tasks };
}

如何解决此问题？我已经在

之类的React useEffect中看到了有关清理的信息

return () => cleanup();

但是我不确定如何实现。谢谢

编辑：更好的代码格式 EDIT2：添加了另一个错误

Answer 1

如所评论；您可以使用useIsMounted，尽管我不会用yarn / npm安装它，而只是将其添加到lib或其他代码中。

export default function CountersContainer() {
  const [val, setVal] = useState([1]);
  useEffect(() => {
    //cause all items to unmount in half a second
    setTimeout(() => setVal([]), 500);
  });
  return (
    <div>
      {val.map(val => (
        <Item val={val} key={val} />
      ))}
    </div>
  );
}
//item will be unmounted in half a second
const Item = ({ val }) => {
  const isMounted = useIsMounted();
  const set = useState()[1];
  useEffect(() => {
    //trying to do a set state after Item is unmounted
    setTimeout(() => {
      //luckily it'll check if it's mounted
      if (isMounted.current) {
        set(22);
      }
    }, 700);
  }, [isMounted, set]);
  return <div>{val}</div>;
};

const useIsMounted = () => {
  const isMounted = useRef(false);
  useEffect(() => {
    isMounted.current = true;
    return () => (isMounted.current = false);
  }, []);
  return isMounted;
};

通过挂钩API

1 个答案: