如何强制组件使用 React 中的钩子重新渲染？

Question

Considering below hooks example

   import { useState } from 'react';

   function Example() {
       const [count, setCount] = useState(0);

       return (
           <div>
               <p>You clicked {count} times</p>
               <button onClick={() => setCount(count + 1)}>
                  Click me
               </button>
          </div>
        );
     }

Basically we use this.forceUpdate() method to force the component to re-render immediately in React class components like below example

    class Test extends Component{
        constructor(props){
             super(props);
             this.state = {
                 count:0,
                 count2: 100
             }
             this.setCount = this.setCount.bind(this);//how can I do this with hooks in functional component 
        }
        setCount(){
              let count = this.state.count;
                   count = count+1;
              let count2 = this.state.count2;
                   count2 = count2+1;
              this.setState({count});
              this.forceUpdate();
              //before below setState the component will re-render immediately when this.forceUpdate() is called
              this.setState({count2: count
        }

        render(){
              return (<div>
                   <span>Count: {this.state.count}></span>. 
                   <button onClick={this.setCount}></button>
                 </div>
        }
 }

But my query is How can I force above functional component to re-render immediately with hooks?

Answer 1

This is possible with useState or useReducer , since useState uses useReducer internally :

const [, updateState] = React.useState();
const forceUpdate = React.useCallback(() => updateState({}), []);

forceUpdate isn't intended to be used under normal circumstances, only in testing or other outstanding cases. This situation may be addressed in a more conventional way.

setCount is an example of improperly used forceUpdate , setState is asynchronous for performance reasons and shouldn't be forced to be synchronous just because state updates weren't performed correctly. If a state relies on previously set state, this should be done with updater function ,

If you need to set the state based on the previous state, read about the updater argument below.

<...>

Both state and props received by the updater function are guaranteed to be up-to-date. The output of the updater is shallowly merged with state.

setCount may not be an illustrative example because its purpose is unclear but this is the case for updater function:

setCount(){
  this.setState(({count}) => ({ count: count + 1 }));
  this.setState(({count2}) => ({ count2: count + 1 }));
  this.setState(({count}) => ({ count2: count + 1 }));
}

This is translated 1:1 to hooks, with the exception that functions that are used as callbacks should better be memoized:

   const [state, setState] = useState({ count: 0, count2: 100 });

   const setCount = useCallback(() => {
     setState(({count}) => ({ count: count + 1 }));
     setState(({count2}) => ({ count2: count + 1 }));
     setState(({count}) => ({ count2: count + 1 }));
   }, []);

Answer 2

Generally, you can use any state handling approach you want to trigger an update.

With TypeScript

codesandbox example

useState

const forceUpdate: () => void = React.useState()[1].bind(null, {})  // see NOTE below

useReducer

const forceUpdate = React.useReducer(() => ({}), {})[1] as () => void

as custom hook

Just wrap whatever approach you prefer like this

function useForceUpdate(): () => void {
  return React.useReducer(() => ({}), {})[1] as () => void // <- paste here
}

---

How this works?

" To trigger an update " means to tell React engine that some value has changed and that it should rerender your component.

[, setState] from useState() requires a parameter. We get rid of it by binding a fresh object {} .
() => ({}) in useReducer is a dummy reducer that returns a fresh object each time an action is dispatched.
{} (fresh object) is required so that it triggers an update by changing a reference in the state.

PS: useState just wraps useReducer internally. source

NOTE: Using .bind with useState causes a change in function reference between renders. It is possible to wrap it inside useCallback as already explained here , but then it wouldn't be a sexy one-liner™ . The Reducer version already keeps reference equality between renders. This is important if you want to pass the forceUpdate function in props.

plain JS

const forceUpdate = React.useState()[1].bind(null, {})  // see NOTE above
const forceUpdate = React.useReducer(() => ({}))[1]

Answer 3

React Hooks FAQ official solution for forceUpdate :

const [_, forceUpdate] = useReducer((x) => x + 1, 0);
// usage
<button onClick={forceUpdate}>Force update</button>

Working example

 const App = () => { const [_, forceUpdate] = useReducer((x) => x + 1, 0); return ( <div> <button onClick={forceUpdate}>Force update</button> <p>Forced update {_} times</p> </div> ); }; ReactDOM.render(<App />, document.getElementById("root"));

 <script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.10.1/umd/react.production.min.js" integrity="sha256-vMEjoeSlzpWvres5mDlxmSKxx6jAmDNY4zCt712YCI0=" crossorigin="anonymous"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.10.1/umd/react-dom.production.min.js" integrity="sha256-QQt6MpTdAD0DiPLhqhzVyPs1flIdstR4/R7x4GqCvZ4=" crossorigin="anonymous"></script> <script>var useReducer = React.useReducer</script> <div id="root"></div>

Answer 4

As the others have mentioned, useState works - here is how mobx-react-lite implements updates - you could do something similar.

Define a new hook, useForceUpdate -

import { useState, useCallback } from 'react'

export function useForceUpdate() {
  const [, setTick] = useState(0);
  const update = useCallback(() => {
    setTick(tick => tick + 1);
  }, [])
  return update;
}

and use it in a component -

const forceUpdate = useForceUpdate();
if (...) {
  forceUpdate(); // force re-render
}

See https://github.com/mobxjs/mobx-react-lite/blob/master/src/utils.ts and https://github.com/mobxjs/mobx-react-lite/blob/master/src/useObserver.ts

Answer 5

Alternative to @MinhKha's answer:

It can be much cleaner with useReducer :

const [, forceUpdate] = useReducer(x => x + 1, 0);

Usage: forceUpdate() - cleaner without params

Answer 6

You can simply define the useState like that:

const [, forceUpdate] = React.useState(0);

And usage: forceUpdate(n => !n)

Hope this help !

Answer 7

You should preferably only have your component depend on state and props and it will work as expected, but if you really need a function to force the component to re-render, you could use the useState hook and call the function when needed.

Example

 const { useState, useEffect } = React; function Foo() { const [, forceUpdate] = useState(); useEffect(() => { setTimeout(forceUpdate, 2000); }, []); return <div>{Date.now()}</div>; } ReactDOM.render(<Foo />, document.getElementById("root"));

 <script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.production.min.js"></script> <script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.production.min.js"></script> <div id="root"></div>

Answer 8

Simple code

const forceUpdate = React.useReducer(bool => !bool)[1];

Use:

forceUpdate();

Answer 9

Potential option is to force update only on specific component using key . Updating the key trigger a rendering of the component (which failed to update before)

For example:

const [tableKey, setTableKey] = useState(1);
...

useEffect(() => {
    ...
    setTableKey(tableKey + 1);
}, [tableData]);

...
<DataTable
    key={tableKey}
    data={tableData}/>

Answer 10

You can (ab)use normal hooks to force a rerender by taking advantage of the fact that React doesn't print booleans in JSX code

// create a hook
const [forceRerender, setForceRerender] = React.useState(true);

// ...put this line where you want to force a rerender
setForceRerender(!forceRerender);

// ...make sure that {forceRerender} is "visible" in your js code
// ({forceRerender} will not actually be visible since booleans are
// not printed, but updating its value will nonetheless force a
// rerender)
return (
  <div>{forceRerender}</div>
)

Answer 11

My variation of forceUpdate is not via a counter but rather via an object:

// Emulates `forceUpdate()`
const [unusedState, setUnusedState] = useState()
const forceUpdate = useCallback(() => setUnusedState({}), [])

Because {} !== {} every time.

Answer 12

Solution in one single line:

const [,forceRender] = useReducer((s) => s+1, 0)

You can learn about useReducer here. https://reactjs.org/docs/hooks-reference.html#usereducer

Answer 13

One line solution:

const useForceUpdate = () => useState()[1];

useState returns a pair of values: the current state and a function that updates it - state and setter , here we are using only the setter in order to force re-render.

Answer 14

react-tidy has a custom hook just for doing that called useRefresh :

import React from 'react'
import {useRefresh} from 'react-tidy'

function App() {
  const refresh = useRefresh()
  return (
    <p>
      The time is {new Date()} <button onClick={refresh}>Refresh</button>
    </p>
  )
}

Learn more about this hook

Disclaimer I am the writer of this library.

Answer 15

This will render depending components 3 times (arrays with equal elements aren't equal):

const [msg, setMsg] = useState([""])

setMsg(["test"])
setMsg(["test"])
setMsg(["test"])

Answer 16

For regular React Class based components, refer to React Docs for the forceUpdate api at this URL. The docs mention that:

Normally you should try to avoid all uses of forceUpdate() and only read from this.props and this.state in render()

However, it is also mentioned in the docs that:

If your render() method depends on some other data, you can tell React that the component needs re-rendering by calling forceUpdate().

So, although use cases for using forceUpdate might be rare, and I have not used it ever, however I have seen it used by other developers in some legacy corporate projects that I have worked on.

So, for the equivalent functionality for Functional Components, refer to the React Docs for HOOKS at this URL. Per the above URL, one can use the "useReducer" hook to provide a forceUpdate functionality for Functional Components.

A working code sample that does not use state or props is provided below, which is also available on CodeSandbox at this URL

import React, { useReducer, useRef } from "react";
import ReactDOM from "react-dom";

import "./styles.css";

function App() {
  // Use the useRef hook to store a mutable value inside a functional component for the counter
  let countref = useRef(0);

  const [, forceUpdate] = useReducer(x => x + 1, 0);

  function handleClick() {
    countref.current++;
    console.log("Count = ", countref.current);
    forceUpdate(); // If you comment this out, the date and count in the screen will not be updated
  }

  return (
    <div className="App">
      <h1> {new Date().toLocaleString()} </h1>
      <h2>You clicked {countref.current} times</h2>
      <button
        onClick={() => {
          handleClick();
        }}
      >
        ClickToUpdateDateAndCount
      </button>
    </div>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

NOTE: An alternate approach using the useState hook (instead of useReducer) is also available at this URL.

Answer 17

There are many ways to force re-render in Hook.

For me simple way with useState() and tip of reference object values.

const [, forceRender] = useState({});

// Anywhre
forceRender({});

Codesandbox Example

Answer 18

const useForceRender = () => {
  const [, forceRender] = useReducer(x => (x + 1) % 2, 0)
  return forceRender
}

Usage

function Component () {
  const forceRender = useForceRender() 
  useEffect(() => {
    // ...
    forceRender()
  }, [])

Answer 19

A bit late to the party but I notice that most (all) of the answers have missed the part where you can pass a callback to forceUpdate lifecycle method.

As per the react source code , this callback has the same behavior as the one in the setState method - it is executed after the update.

Hence, the most correct implementation would be like this:

 /** * Increments the state which causes a rerender and executes a callback * @param {function} callback - callback to execute after state update * @returns {function} */ export const useForceUpdate = (callback) => { const [state, updater] = useReducer((x) => x + 1, 0); useEffect(() => { callback && callback(); }, [state]); return useCallback(() => { updater(); }, []); };

Answer 20

I was working with an array and spotted this issue. However, instead of explicit forceUpdate I found another approach - to deconstruct an array and set a new value for it using this code:

    setRoutes(arr => [...arr, newRoute]); // add new elements to the array
    setRouteErrors(routeErrs => [...routeErrs]); // the array elements were changed

I found it very interesting that setting even a copy of an array will not trigger the hook. I assume React does the shallow comparison