Reactjs 为select设置默认值

这是我的SearchForm.js类，

period

是一个选择列表

import React from 'react';
import ReactDOM from 'react-dom';
import axios from 'axios';

class SearchForm extends React.Component {

        constructor(props) {
            super(props)

            this.state = {
                position: '',
                area: '',
                period: '',
                experience: {
                    type: Array,
                    default: () => []
                }
            }
            this.handlePeriodChange = this.handlePeriodChange.bind(this);
        }


        handlePeriodChange(e) {
            this.setState({
                [e.target.name]: e.target.value
            });
        }      

        render() {
            return ( <
                form className = 'form search-form'
                onSubmit = {
                    this.handleSubmit
                } >
                <
                div className = "form-row" >

                    <
                    div className = "form-group col-md-2" >
                    <
                    label htmlFor = "period" > Period *< /label> <
                    select className = "form-control"
                    name = "period"
                    id = "period"
                    onChange = {
                        this.handlePeriodChange
                    }
                    value = {
                        this.state.period
                    } >
                    <
                    option value = "1" > 1 < /option> <
                    option value = "3" > 3 < /option> <
                    option value = "7" > 7 < /option> <
                    option value = "30" > 30 < /option> < /
                    select > <
                    /div> < /
                    div >


                    <
                    div className = "form-row" >
                    <
                    div className = "form-group col-md-12 pt-3" >
                    <
                    input id = 'form-button'
                    className = 'btn btn-primary'
                    type = 'submit'
                    placeholder = 'Send' / >
                    <
                    /div> < /
                    div > <
                    /form>
                )
            }
        }

        export {
            SearchForm
        }

从“React”导入React；
从“react dom”导入react dom；
从“axios”导入axios；
类SearchForm扩展了React.Component{
建造师（道具）{
超级（道具）
此.state={
位置：“”，
区域：“”，
期间：“”，
经验：{
类型：数组，
默认值：（）=>[]
}
}
this.handlePeriodChange=this.handlePeriodChange.bind（this）；
}
手周期变化（e）{
这是我的国家({
[e.target.name]：e.target.value
});
}      
render（）{
报税表（<
表单类名称='表单搜索表单'
onSubmit={
这是我的手稿
} >
<
div className=“表格行”>
<
div className=“表格组col-md-2”>
<
标签htmlFor=“period”>period*<
选择className=“表单控件”
name=“期间”
id=“期间”
onChange={
这是一个周期性的变化
}
值={
这段时间
} >
<
选项值=“1”>1<
选项值=“3”>3<
选项值=“7”>7<
选项值=“30”>30/
选择><
/div>
<
div className=“表格行”>
<
div className=“表格组col-md-12 pt-3”>
<
输入id='表单按钮'
className='btn btn primary'
类型='submit'
占位符='发送'/>
<
/div><
/表格>
)
}
}
出口{
搜索表单
}

---

如何设置时段

选择的默认值？
在状态中为选择选项提供默认值

 this.state = {
            position: '',
            area: '',
            period: '1',
            experience: {
                type: Array,
                default: () => []
            }
        }
       ...
 <select 
      className = "form-control"
      name = "period"
      id = "period"
      onChange = {this.handlePeriodChange}
      value = {this.state.period
      }
 >
      <option value = "1" > 1 < /option> 
      <option value = "3" > 3 < /option> 
      <option value = "7" > 7 < /option> 
      <option value = "30" > 30 < /option>
 < /select >

在状态中为选择选项提供默认值

 this.state = {
            position: '',
            area: '',
            period: '1',
            experience: {
                type: Array,
                default: () => []
            }
        }
       ...
 <select 
      className = "form-control"
      name = "period"
      id = "period"
      onChange = {this.handlePeriodChange}
      value = {this.state.period
      }
 >
      <option value = "1" > 1 < /option> 
      <option value = "3" > 3 < /option> 
      <option value = "7" > 7 < /option> 
      <option value = "30" > 30 < /option>
 < /select >

this.state.period未加载默认值？在this.state.period中指定一个值并选中此项，然后请格式化您的代码this.state.period是否未加载默认值？在this.state.period中指定一个值，并选中此项，然后请格式化代码