javascript - 如何在此React组件中分解对象的状态数组以使用单个字段数据

提取后，组件状态下的数组中有96个对象。它们是唯一的对象，除了年份，在某些情况下还包括月份。不能静态设置年份，因为它会在某个时候明显改变。月份将从Integer转换为String。我尝试将其映射，但出现错误消息cannot read property map of undefined。但是，如果我console.log数据，它将得到具有96个对象的数组。当我尝试对其进行分解时，出现错误Invalid attempt to destructure non-iterable instance。我的主要目标是采用年份并将其作为模板文字传递给headerName，以便将其作为以下所有数据的分组列加载。并采用月份整数并将其转换为该月份的字符串，该组件的代码如下。

import React, { Component } from "react";
import { AgGridReact } from "ag-grid-react";

class ColumnGroups extends Component {
  constructor(props) {
    super(props);

    this.state = {
      columnDefs: [
        {
          headerName: "Year",
          field: "year",
          children: [
            {
              headerName: "Month",
              field: "month",
              width: 150,
              children: [
                  {
                  headerName: "Sold",
                  field: "sales",
                  width: 150
              },
              {
                  headerName: "Return",
                  field: "returns",
                  width: 150
              },
              {
                  headerName: "RMA%",
                  field: "rma",
                  width: 150
              }
                  ]
              }

              ],
              defaultColDef: {
                  editable: false,
                  sortable: true,
                  resizable: true,
                  filter: true
                },
                rowSelection: "multiple",
                rowGroupPanelShow: "always",
                pivotPanelShow: "always",
                paginationPageSize: 10,
                paginationNumberFormatter: function(params) {
                  return "[" + params.value.toLocaleString() + "]";
                },
                rowData: []


          }

      ],
  }

  }
  onGridReady = params => {
    this.gridApi = params.api;
    this.gridColumnApi = params.columnApi;

    const httpRequest = new XMLHttpRequest();
    const updateData = data => {
      this.setState({ rowData: data });
      params.api.paginationGoToPage(4);
    };

    httpRequest.open(
      "GET",
      "http://localhost:5000/api/salessummary"
    );
    httpRequest.send();
    httpRequest.onreadystatechange = () => {
      if (httpRequest.readyState === 4 && httpRequest.status === 200) {
        updateData(JSON.parse(httpRequest.responseText));
      }
    };
  };

  onPageSizeChanged(newPageSize) {
    var value = document.getElementById("page-size").value;
    this.gridApi.paginationSetPageSize(Number(value));
  }

render() {
  {console.log(this.state.rowData)}
    return (
        <div>
            <div>
                <div
    className="ag-theme-balham"
    style={{
    height: '500px',
    width: '100%' }}
  >
      <div className="test-header">
        Page Size:
        <select onChange={this.onPageSizeChanged.bind(this)} id="page-size">
          <option value="10" selected="">
            10
          </option>
          <option value="100">100</option>
          <option value="500">500</option>
          <option value="1000">1000</option>
        </select>
      </div>
    <AgGridReact
      columnDefs={this.state.columnDefs}
      rowData={this.state.rowData}
      autoGroupColumnDef={this.state.autoGroupColumnDef}
      defaultColDef={this.state.defaultColDef}
      suppressRowClickSelection={true}
      groupSelectsChildren={true}
      debug={true}
      rowSelection={this.state.rowSelection}
      rowGroupPanelShow={this.state.rowGroupPanelShow}
      pivotPanelShow={this.state.pivotPanelShow}
      enableRangeSelection={true}
      pagination={true}
      paginationPageSize={this.state.paginationPageSize}
      paginationNumberFormatter={this.state.paginationNumberFormatter}
      onGridReady={this.onGridReady}
      >

    </AgGridReact>
  </div>
            </div>
        </div>

    )
}
}
export default ColumnGroups;

这是回来的部分无法读取未定义的属性“ map”

   <div>
           {
    this.state.rowData.map(data => <div>{data.year}</div> )
  }
</div>

数据如下

{
"year": 2019,
"month": 4,
"productStyle": "zzzzz",
"sales": 1,
"returns": 0,
"rma": 0
},

每年是完全一样的。映射返回了96年中我不需要的95年。它将改变，我希望这对于现场年份而言是动态的。而且我需要访问月份，以便可以将四月份的integer更改为string 3。

最佳答案

没有内置的JS方法可将Month数字格式化为可自行构建的字符串：

numToMonth(n){
    switch(n){
        case 1:
           return 'Jan'
        //... all months
        default:
           return 'Dec'
        }
}

您需要先验证，然后再进行映射。要更彻底地检查它是否存在及其数组：

render(){
    if(this.state.rowData && Array.isArray(this.state.rowData)){
        var items = this.state.rowData
    }
    return(
        <div>
            {items && items.map(item => <div>{item.Year}</div> )}
        </div>
    )
  }
}

如果您需要根据当年使用的一项，请查找：

render(){
    if(this.state.rowData && Array.isArray(this.state.rowData)){
        var item = this.state.rowData.find(data => data.year === new Date().getFullYear )
    }

    return(
        <div>
            {item && `${item.year} - ${this.numToMonth(item.month)}` }
        </div>
    )
}

如果您需要基于当前年份过滤器的许多项目：

render(){
    if(this.state.rowData && Array.isArray(this.state.rowData)){
        var items = this.state.rowData.filter(data => data.year === new Date().getFullYear )
    }

    return(
        <div>
            {item && items.map(items=> <div>{item.year} - {this.numToMonth(item.month)} </div>})
        </div>
    )
}

如果所有年份都相同，并且您需要和一串月份数字作为字符串：

render(){
    if(this.state.rowData && Array.isArray(this.state.rowData)){
        var items = this.state.rowData
    }
    return(
        <div>
            {items && items[0].year}
            {items && items.map(item => <div>{this.numToMonth(item.month)}</div> )}
        </div>
    )
  }
}

最后一个示例的可运行代码段：

class SomeComponent extends React.Component {
  state={
    rowData:[
      {year:1988,month:1},
      {year:1988,month:3},
      {year:1988,month:2},
      {year:1988,month:1},
    ]
  }
  numToMonth(n){
    switch(n){
        case 1:
           return 'Jan'
        case 2:
           return 'Feb'
        case 3:
           return 'March'
        //... all months
        default:
           return 'Dec'
        }
  }
  render(){
    if(this.state.rowData && Array.isArray(this.state.rowData)){
        var items = this.state.rowData
    }
    return(
        <div>
            {items && items[0].year}
            {items && items.map(item => <div>{this.numToMonth(item.month)}</div> )}
      </div>
    )
  }
}

ReactDOM.render(
  <SomeComponent />,
  document.getElementById("react")
);

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.4/umd/react.production.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.4/umd/react-dom.production.min.js"></script>

<div id="react"></div>