React - 表单
React - 组合 vs 继承

React - 状态提升

violet posted @ Jul 18, 2020 08:30:43 AM in 读书笔记 with tags React , 10549 阅读

在 React 应用中,任何可变数据应当只有一个相对应的唯一“数据源”。通常,state 都是首先添加到需要渲染数据的组件中去。然后,如果其他组件也需要这个 state,那么你可以将它提升至这些组件的最近共同父组件中。你应当依靠自上而下的数据流,而不是尝试在不同组件间同步 state。
虽然提升 state 方式比双向绑定方式需要编写更多的“样板”代码,但带来的好处是,排查和隔离 bug 所需的工作量将会变少。由于“存在”于组件中的任何 state,仅有组件自己能够修改它,因此 bug 的排查范围被大大缩减了。此外,你也可以使用自定义逻辑来拒绝或转换用户的输入。
如果某些数据可以由 props 或 state 推导得出,那么它就不应该存在于 state 中。

 

const scaleNames = {
  c: 'Celsius',
  f: 'Fahrenheit'
};

function toCelsius(fahrenheit) {
  return (fahrenheit - 32) * 5 / 9;
}

function toFahrenheit(celsius) {
  return (celsius * 9 / 5) + 32;
}

function tryConvert(temperature, convert) {
  const input = parseFloat(temperature);
  if (Number.isNaN(input)) {
    return '';
  }
  const output = convert(input);
  const rounded = Math.round(output * 1000) / 1000;
  return rounded.toString();
}


function BoilingVerdict(props) {
  if (props.celsius >= 100) {
    return <p>The water would boil.</p>
  }
  return <p>The water would not boil.</p>
}

class TemperatureInput extends React.Component {
  constructor(props) {
    super(props);
    this.handleChange = this.handleChange.bind(this);
    this.state = {temperature: ''};
  }
  
  handleChange(e) {
    this.props.onTemperatureChange(e.target.value);
  }
  
  render() {
    const temperature = this.props.temperature;
    const scale = this.props.scale;
    return (
      <fieldset>
        <legend>Enter temperature in {scaleNames[scale]}:</legend>
        <input value={temperature}
          onChange={this.handleChange} />
      </fieldset>
    );
  }
}


class Calculator extends React.Component {
  constructor(props) {
    super(props);
    this.handleCelsiusChange = this.handleCelsiusChange.bind(this);
    this.handleFahrenheitChange = this.handleFahrenheitChange.bind(this);
    this.state = {temperature: '', scale: 'c'};
  }
  
  handleCelsiusChange(temperature) {
    this.setState({scale: 'c', temperature});
  }
  
  handleFahrenheitChange(temperature) {
    this.setState({scale: 'f', temperature});
  }

  render() {
    const scale = this.state.scale;
    const temperature = this.state.temperature;
    const celsius = scale === 'f' ? tryConvert(temperature, toCelsius) : temperature;
    const fahrenheit = scale === 'c' ? tryConvert(temperature, toFahrenheit) : temperature;
    return (
      <div>
        <TemperatureInput
          scale="c"
          temperature={celsius}
          onTemperatureChange={this.handleCelsiusChange} />
        <TemperatureInput 
          scale="f"
          temperature={fahrenheit}
          onTemperatureChange={this.handleFahrenheitChange} />
        <BoilingVerdict
          celsius={parseFloat(celsius)} />
      </div>
    );
  }
}

ReactDOM.render(
  <Calculator />,
  document.getElementById('root')
)
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