登录页面可以获取页面localStorage的默认值，登录获取输入框的值发送给后台，重置清空输入框的值

1.0 父子通信版本

父组件

import React, { Component } from 'react'
import Field from './components/Field'
import Button from './components/Button'
export default class App extends Component {
    state = {
        username: 'default value' || localStorage.getItem('username'),
        password: ''
    }
    render() {
        return (
            <div>
                <h2>登录页面</h2>
                <Field label="用户名" type="text" onChangeEvent={(value) => { this.setState({ username: value }) }} value={this.state.username} ></Field>
                <Field label="密码" type="password" onChangeEvent={(value) => { this.setState({ password: value }) }} value={this.state.password}></Field>
                <div style={{ display: 'flex', 'marginLeft': '110px' }}>
                    <Button type="button" value="登录" event={() => { console.log(this.state.username, this.state.password, '发送后端验证'); }} />
                    <Button type="button" value="重置" event={() => {
                        this.setState({ username: '', password: '' })
                    }} />
                </div>
            </div>
        )
    }
}

子组件: 输入框

import React, { Component } from 'react'
export default class Field extends Component {
  render() {
    return (
        <div style={{display: 'flex',margin: '10px'}}>
            <label style={{width:'100px',display: 'block'}}>{this.props.label}: </label>
            <input style={{ width: '200px', height: '25px', padding: '0px 5px' }} type={this.props.type} onChange={(event) => {
                this.props.onChangeEvent(event.target.value)
            }} value={this.props.value}/>
      </div>
    )
  }
}

子组件: 按钮

import React, { Component } from 'react'

export default class Button extends Component {
  render() {
    return (
        <div>
            <button style={{cursor:'pointer','marginRight':'20px'}} type={this.props.type} onClick={this.props.event}  >{this.props.value}</button>
      </div>
    )
  }
}

2.0 ref通信版本

父组件

import React, { Component } from 'react'
import Field from './components/Field-5'
import Button from './components/Button'
export default class App extends Component {
    username = React.createRef()
    password = React.createRef()
    render() {
        return (
            <div>
                <h2>登录页面</h2>
                <Field label="用户名" type="text"  ref={this.username} ></Field>
                <Field label="密码" type="password" ref={this.password}  ></Field>
                <div style={{ display: 'flex', 'marginLeft': '110px' }}>
                    <Button type="button" value="登录" event={() => { console.log(this.username.current,this.username.current.state.value,this.password.current.state.value) }} />
                    <Button type="button" value="重置" event={() => {
                        this.username.current.clear();
                        this.password.current.clear();
                    }} />
                </div>
            </div>
        )
    }
}

子组件

import React, { Component } from 'react'
export default class Field extends Component {
    state = {
      value:''
    }  
    clear() {
        this.setState({value:''})
    }
  render() {
    return (
        <div style={{display: 'flex',margin: '10px'}}>
            <label style={{width:'100px',display: 'block'}}>{this.props.label}: </label>
            <input style={{ width: '200px', height: '25px', padding: '0px 5px' }} type={this.props.type} onChange={(event) => {
                this.setState({
                    value: event.target.value
                })
            }} value={this.state.value}/>
      </div>
    )
  }
}