无法在React中读取未定义的属性"map"

Question

我有一个从容器组件调用的以下组件.容器组件传递事务prop.

我知道prop中的data属性正在传递,并且有数据,可以从console.log调用访问.但是,当我尝试映射数据并创建列表时,我收到一个错误:Cannot read property 'map' of undefined

以下是数据的样子:

[
{"transid":3426,"acct":"acct1","category":"Auto"},
 {"transid":3427,"acct":"acct2","category":"Subscriptions"}
]

我究竟做错了什么？

import React from 'react';


export default function TransactionManagerView (props) {

  console.log(props.data);

  return (
    <ul>
      {
        props.data.map(function(el,index) {
           return <li key={index}>{el.category}</li>
        })
      }
    </ul>
  )

}

Answer 1

提供对undefined的检查prop.data,然后渲染组件,因为props最初可能不提供数据,但在第二个渲染中可用.那应该可以解决你的问题

class App extends React.Component {
  render() {
    var data = [
{"transid":3426,"acct":"acct1","category":"Auto"},
 {"transid":3427,"acct":"acct2","category":"Subscriptions"}
]
    return (
        <div ><TransactionManagerView data={data}/></div>
    )
  }

}



const TransactionManagerView = function(props) {

  console.log(props.data);

  return (
    <ul>
      {
        props.data && props.data.map(function(el,index) {
           return <li key={index}>{el.category}</li>
        })
      }
    </ul>
  )

}

ReactDOM.render(<App/>, document.getElementById('app'));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/0.14.8/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/0.14.8/react-dom.min.js"></script>
<div id="app"></div>