问useEffect中的useState不更新状态

EN

import React, { useState, useEffect } from "react";
import { Route, Redirect } from "react-router-dom";
import { checkLoggedIn } from "utils/Api";

export const Auth = (props) => {
  const [currentUser, setCurrentUser] = useState(null);
  const [isLoading, setIsLoading] = useState(false);
  console.log(currentUser);

  useEffect(() => {
    const f = async () => {
      setIsLoading(true);
      console.log(isLoading);
      const res = await checkLoggedIn();
      if (!!res) { // ==> true
        setCurrentUser(res);
        console.log(currentUser); // ==> null!
      }
      setIsLoading(false);
    };
    f();
  });

  if (isLoading) {
    return <div>loading</div>;
  }

  console.log(currentUser); // ==> null!
  return !!currentUser ? (
    <Route children={props.children} />
  ) : (
    <Redirect to={"/login"} />
  );
};