为什么即使使用useCallback后状态也始终为0

Question

I expect it should be a time counter. useCallback will refresh after the time change, so time will be 1 in the second time, but still is 0

I tried to use useCallback but didn't work

import React, { useState, useEffect, useCallback } from 'react';
import { render } from 'react-dom';
import './style.css';

import {interval} from 'rxjs'
import { take } from 'rxjs/operators';

const inter$ = interval(1000);

function App(){
  const [time, setTime] = useState(0);
  const callback = useCallback(()=> {
      setTime(time+1);
      console.log('hella');
    }, [time])

  useEffect(()=>{
    console.log('hello')
    inter$.subscribe(callback)

  }, [])

  return <div>{time}</div>
}


render(<App />, document.getElementById('root'));

always show 1

this is the code

Answer 1

Inside useEffect the callback doesn't change since it's not a dependency. Thus, the time inside the subscription callback is always 0.

Working solution with Rx.js :
setTime call is based on prevState inside callback function.

import React, { useState, useEffect } from "react";
import { render } from "react-dom";
import "./style.css";

import { interval } from "rxjs";
import { take } from "rxjs/operators";

const inter$ = interval(1000);

function App() {
  const [time, setTime] = useState(0);

  useEffect(() => {
    console.log("hello");
    inter$.subscribe(() => {
      setTime(prevTime => prevTime + 1);
      console.log("hella");
    });
  }, []);

  return <div>{time}</div>;
}

render(<App />, document.getElementById("root"));

Answer 2

change setTime(time+1); to setTime(time=>time+1); Heres the full code :

import React, { useState, useEffect, useCallback } from 'react';
import { render } from 'react-dom';
import './style.css';

import {interval} from 'rxjs'
import { take } from 'rxjs/operators';

const inter$ = interval(1000);

function App(){
  const [time, setTime] = useState(0);
  const callback = useCallback(()=> {
      setTime(time=>time+1);
      console.log('hella');
    }, [time])

  useEffect(()=>{
    console.log('hello')
    inter$.subscribe(callback)

  }, [])

  return <div>{time}</div>
}



render(<App />, document.getElementById('root'));

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