javascript - 转发引用 : forwardedRef is always null

Question

我有一个 ant design Table 组件，我希望将 ref 附加到该组件。

我希望能够在 HOC withCustomPagination 的生命周期 componentDidUpdate 方法中使用 tableRef。

在 React Docs Forwarding Refs 之后，我无法清楚地理解。我可以编写以下代码:

App.js

import WrappedTable from '/path/to/file';

class App extends React.Component {
  render() {
    const tableRef = React.createRef();
    return (
      <WrappedTable ref={tableRef} />
    )
  }
}

Table.js

import withCustomPagination from '/path/to/file';

class Table extends React.Component {
  constructor(props) {
    super(props); 
  }

  render() {
    <TableContainer ref={this.props.forwardedRef} />
  }
}

const WrappedTable = withCustomPagination(Table);
export default WrappedTable;

withCustomPagination.js

import CustomPagination from 'path/to/file';

const withCustomPagination = tableRef => Component => {
  class WithCustomPagination extends React.Component {
    constructor(props) {
      super(props);
      this.state = {
        rows: 1,
        dataLength: props.dataLength,
      }
    }

    componentDidUpdate() {
      tableRef.current.state ..... //logic using ref, Error for this line
      this.state.rows ..... //some logic
    }

    render() {
      const { forwardedRef } = this.props;
      return (
        <Component {...this.state} ref={forwardedRef} />
        <CustomPagination />
      )
    }
  }
  return React.forwardRef((props, ref) => {
    return <WithCustomPagination {...props} forwardedRef={ref} />;
  });
}

export default withCustomPagination;

调试后发现forwardedRef一直为null。

Answer 1

您的问题发生在您的 HOC 中:

                              here
const withCustomPagination = tableRef => Component => {

您需要删除该参数。访问 ref prop 的方法很简单，就是在你的 componentDidUpdate 方法中，比如 forwardedRef prop 例如:

import CustomPagination from 'path/to/file';

const withCustomPagination = Component => {
  class WithCustomPagination extends React.Component {
    constructor(props) {
      super(props);
      this.state = {
        rows: 1,
        dataLength: props.dataLength,
      }
    }

    componentDidUpdate() {
      //You got the ref here
      console.log(forwardedRef.current)
    }

    render() {
      const { forwardedRef } = this.props;
      return (
        <Component {...this.state} ref={forwardedRef} />
        <CustomPagination />
      )
    }
  }
  return React.forwardRef((props, ref) => {
    return <WithCustomPagination {...props} forwardedRef={ref} />;
  });
}

export default withCustomPagination;

还需要考虑的是:

您不应该在渲染方法中创建 ref，因为每次设置状态时都会引发此方法。我建议您在构造函数中执行此操作:

import WrappedTable from '/path/to/file';

class App extends React.Component {
  constructor(){
    super();
    this.reference = React.createRef();
  }
  render() {
    return (
      <WrappedTable ref={this.reference} />
    )
  }
}

同样在你的 HOC 中只渲染一个 child 或使用 React.Fragment。此外不要忘记发送其余属性:

const withCustomPagination = Component => {
  class WithCustomPagination extends React.Component {
    constructor(props) {
      super(props);
      this.state = {
        rows: 1,
        dataLength: props.dataLength,
      }
    }

    componentDidUpdate() {
      //You got the ref here
      console.log(forwardedRef.current)
    }

    render() {
      // Do not forget to send the rest of properties here like:
      const { forwardedRef, ...rest } = this.props;
      return (
        <React.Fragment>
          <Component {...this.state} ref={forwardedRef} {...rest} />
          <CustomPagination />
        </React.Fragment>
      )
    }
  }
  return React.forwardRef((props, ref) => {
    return <WithCustomPagination {...props} forwardedRef={ref} />;
  });
}

export default withCustomPagination;

编辑:

添加 ref 属性的引用

import withCustomPagination from '/path/to/file';

class Table extends React.Component {
  constructor(props) {
    super(props); 
    this.reference = React.createRef();
  }

  render() {
    <TableContainer ref={this.reference} />
  }
}

const WrappedTable = withCustomPagination(Table);
export default WrappedTable;