React 16 中的 Fragment 映射

Question

我正在尝试映射片段的子级，而该片段又是组件的子级。例如：

const Frag = () => (
  <React.Fragment key="test-key">
    <div>test1</div>
    <div>test2</div>
  </React.Fragment>
);

const Outer = ({ children }) => (
  <div>
    {
      React.Children.map(children, (child) => (
        <a>
          {child}
        </a>
      ))
    }
  </div>
);

// Usage
<Outer>
  <Frag />
</Outer>

这将导致单个

a

标签，即使片段内部有多个 div。文档（https://reactjs.org/docs/react-api.html#reactchildrenmap）似乎表明这应该与键控片段一起使用，我认为我正在正确创建一个键控片段（https:// Reactjs.org/docs/fragments.html#keyed-fragments）。任何帮助将不胜感激！

Answer 1

是的，但据我所知 - 您正在迭代

Outer

孩子。 尝试

React.Children.map(children[0].props.children, (child) => (

但是，仔细查看您的链接 - 我发现文档在这里说错了

该函数永远不会传递容器对象

这是一个示例，清楚地表明容器被传递给函数：

<script src="https://unpkg.com/@babel/standalone/babel.js"></script>
<script src="https://unpkg.com/[email protected]/umd/react.development.js"></script>
<script src="https://unpkg.com/[email protected]/umd/react-dom.development.js"></script>
<div id="root" />
<script type="text/babel">
  const Frag = () => (
    <>
      <div>test1</div>
      <div>test2</div>
    </>
  ); 
  
  const Outer = ({ children }) => (
    <div>
      { 
        React.Children.map(children, (child) => console.log(`Child type is ${child.type.name || child.type.toString()}`) || (
        <a>
          {child}
        </a> )) 
      }
    </div>
  ); 
  
  
  ReactDOM.render((
    <div>
      <Outer>
        <>
          <div>test1</div>
          <div>test2</div>
        </>
      </Outer>
      <Outer>
        <Frag />
      </Outer>
    </div>
  ), document.getElementById('root'));
</script>

Answer 2

不要使用

React.Children.map

，而是使用此

flatMapChildren

函数来展平

<>fragments</>

以及数组：

import { Children } from 'react';

// TypeScript version
export function flatMapChildren<R>(children: React.ReactNode, fn: (x: React.ReactNode) => R) {
    let results: R[] = [];
    flatForEachChild(children, child => results.push(fn(child)));
    return results;
}

export function flatForEachChild(children: React.ReactNode, action: (x: React.ReactNode) => void) {
    if (isFragment(children)) {
        flatForEachChild(children.props.children, action);
    } else {
        Children.forEach(children, child => {
            if (isFragment(child))
                flatForEachChild(child.props.children, action);
            else
                action(child);
        });
    }
}

const REACT_FRAGMENT = Symbol.for('react.fragment');

export function isFragment(node: React.ReactNode): node is React.ReactElement<{ children: React.ReactNode }> {
    return (node as any)?.type === REACT_FRAGMENT;
}


// JavaScript version
export function flatForEachChild(children, action) {
    if (isFragment(children)) {
        flatForEachChild(children.props.children, action);
    } else {
        Children.forEach(children, child => {
            if (isFragment(child))
                flatForEachChild(child.props.children, action);
            else
                action(child);
        });
    }
}

export function flatMapChildren(children, fn) {
    let results = [];
    flatForEachChild(children, child => results.push(fn(child)));
    return results;
}

const REACT_FRAGMENT = Symbol.for('react.fragment');

export function isFragment(node) {
    return node != null && node.type === REACT_FRAGMENT;
}