状态提升

多个组件需要反映相同state的变化数据时，将共享状态提升到共同的父组件中去。

function BoilingVerdict(props) {
  if (props.celsius >= 100) {
    return <p> 水开了 </p>;
  }
  return <p> 水没开 </p>;
}
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 toCelsius(fahrenheit) {
  return ((fahrenheit - 32) * 5) / 9;
}

function toFahrenheit(celsius) {
  return (celsius * 9) / 5 + 32;
}
const scaleNames = {
  c: "摄氏度",
  f: "华氏度",
};
class TemperatureInput extends React.Component {
  constructor(props) {
    super(props);
    this.handleChange = this.handleChange.bind(this);
  }
  handleChange(e) {
    this.props.onTemperatureChange(e.target.value);
  }
  render() {
    const temperature = this.props.temperature;
    const scale = this.props.scale;
    return (
      <fieldset>
        <legend>输入{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"));

相当于VUE中的注册事件$emit。子组件调用父组件中的方法。

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