React –向数组映射添加唯一键 [英] React – Add unique key to array map

问题描述

我想向此函数提供的返回元素添加唯一键.

I would like to add a unique key to the returned elements this function provides.

function RowList() {
  const rows = [<Row0 />, <Row1 />, <Row2 />, <Row3 />];
  return (
    <>
      {rows.map(row => (
        <tr key={?}>{row}</tr>
      ))}
    </>
  );
}

我尝试过:

function Rows() {
  const rows = [<Row0 />, <Row1 />, <Row2 />, <Row3 />];
  return (
    <>
      {rows.map(row => (
        <tr key={row}>{row}</tr>
      ))}
    </>
  );
}

但是返回[object Object]作为密钥.

我也将不能执行类似

let x = 0
function Rows() {
  const rows = [<Row0 />, <Row1 />, <Row2 />, <Row3 />];
  return (
    <>
      {rows.map(row => (
        <tr key={x = x + 1}>{row}</tr>
      ))}
    </>
  );
}

因为我将需要在以后删除并添加回阵列.

As I will need to be able to remove and add back to the array later.

推荐答案

您知道，您不能只是这样做:

As you know, you can't just do this:

// DON'T DO THIS
{rows.map((row, index) => (
  <tr key={index}>{row}</tr>
))}

如文档所述，这是最后的选择"并且实际上仅对静态列表有用.您说过您的列表不会是静态的.

As the documentation says, that's a "last resort" and really only useful for static lists. You've said your list won't be static.

具有这样已经创建的元素数组而不是元素的 data 数组是非常不寻常的.如果可以避免，我会给数据条目以持久的ID值，您可以将其用作键，例如(name显然是实际数据的替代物):

It's fairly unusual to have an array of already-created elements like that rather than an array of the data for the elements. If you can avoid it, I would, and give the data entries enduring ID values that you can use as keys, e.g. (name is obviously a stand-in for actual data):

class RowInfo {
  static id = 0;
  constructor(name) {
    this.name = name;
    this.id = RowInfo.id++;
  }
}

function RowList() {
  const rows = [new RowInfo("one"), new RowInfo("two"), new RowInfo("three"), new RowInfo("four")];
  return (
    <>
      {rows.map(({id, name}) => (
        <tr key={id}><Row name={name}/></tr>
      ))}
    </>
  );
}

当然，它们都应该是同一类型的组件，但这可能不是正确的.

That assumes that they should all be the same type of component, of course, which may not be true.

如果您不能这样做并且必须预先创建实际的元素，则可能会创建包装对象:

If you can't do that and must pre-create the actual elements, I'd probably create wrapper objects:

class RowInfo {
   static id = 0;
   constructor(element) {
     this.element = element;
     this.id = RowInfo.id++;
   }
}
function RowList() {
  const rows = [new RowInfo(<Row0 />), new RowInfo(<Row1 />), new RowInfo(<Row2 />), new RowInfo(<Row3 />)];
  return (
    <>
      {rows.map(({id, element}) => (
        <tr key={id}>{element}</tr>
      ))}
    </>
  );
}

或者如果它们没有您需要指定的任何道具，您可以让React跟踪它们，因为这是其工作的一部分:

Or if they don't have any props you need to specify, you can let React keep track of them, as that's part of its job:

class RowInfo {
   static id = 0;
   constructor(Comp) {
     this.Comp = Comp;
     this.id = RowInfo.id++;
   }
}
function RowList() {
  const rows = [new RowInfo(Row0), new RowInfo(Row1), new RowInfo(Row2), new RowInfo(Row3)];
  return (
    <>
      {rows.map(({id, Comp}) => (
        <tr key={id}><Comp/></tr>
      ))}
    </>
  );
}

这是一个生动的例子:

const Row0 = () => <div>Row 0</div>;
const Row1 = () => <div>Row 1</div>;
const Row2 = () => <div>Row 2</div>;
const Row3 = () => <div>Row 3</div>;

const {Fragment} = React;

class RowInfo {
   static id = 0;
   constructor(Comp) {
     this.Comp = Comp;
     this.id = RowInfo.id++;
   }
}
// Have to use <Fragment></Fragment> in the below instead of <></> because
// Stack Snippet's version of Babel is out of date and
// doesn't understand <></>.
function RowList() {
  const rows = [new RowInfo(Row0), new RowInfo(Row1), new RowInfo(Row2), new RowInfo(Row3)];
  return (
    <Fragment>
      {rows.map(({id, Comp}) => (
        <tr key={id}><Comp/></tr>
      ))}
    </Fragment>
  );
}

ReactDOM.render(<RowList/>, document.getElementById("root"));

<div id="root"></div>

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.6/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.6/umd/react-dom.production.min.js"></script>

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