javascript - 如何在 React 中使用 hooks 强制组件重新渲染？

Question

考虑下面的钩子(Hook)示例

   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>
        );
     }

基本上，我们使用 this.forceUpdate() 方法强制组件在 React 类组件中立即重新渲染，如下例所示

    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>
        }
 }

但是我的疑问是如何强制上述功能组件立即使用钩子(Hook)重新渲染？

Answer 1

这可以通过 useState 或 useReducer 实现，因为 useState uses useReducer internally :

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

forceUpdate 不适合在正常情况下使用，仅在测试或其他 Unresolved 情况下使用。这种情况可以通过更传统的方式来解决。

setCount 是错误使用 forceUpdate 的示例，出于性能原因，setState 是异步的，不应仅仅因为它而强制同步状态更新未正确执行。如果状态依赖于先前设置的状态，则应使用 updater function 来完成,

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 guaranteedto be up-to-date. The output of the updater is shallowly merged withstate.

setCount 可能不是一个说明性示例，因为其目的尚不清楚，但更新程序函数就是这种情况:

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

这被 1:1 转换为钩子(Hook)，但用作回调的函数应该更好地被记住:

   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 }));
   }, []);