通过这样做来获得输入字段值:

import React, { Component } from 'react';

class App extends Component {

constructor(props){
super(props);

this.state = {
  username : ''
}

this.updateInput = this.updateInput.bind(this);
this.handleSubmit = this.handleSubmit.bind(this);
}


updateInput(event){
this.setState({username : event.target.value})
}


handleSubmit(){
console.log('Your input value is: ' + this.state.username)
//Send state to the server code
}



render(){
return (
    <div>
    <input type="text" onChange={this.updateInput}></input>
    <input type="submit" onClick={this.handleSubmit} ></input>
    </div>
  );
}
} 

//output
//Your input value is: x

// On the state
constructor() {
  this.state = {
   email: ''
 }
}

// Input view ( always check if property is available in state {this.state.email ? this.state.email : ''}

<Input 
  value={this.state.email ? this.state.email : ''} 
  onChange={event => this.setState({ email: event.target.value)}
  type="text" 
  name="emailAddress" 
  placeholder="johdoe@somewhere.com" />

通过这样做来获得输入字段值:

import React, { Component } from 'react';

class App extends Component {

constructor(props){
super(props);

this.state = {
  username : ''
}

this.updateInput = this.updateInput.bind(this);
this.handleSubmit = this.handleSubmit.bind(this);
}


updateInput(event){
this.setState({username : event.target.value})
}


handleSubmit(){
console.log('Your input value is: ' + this.state.username)
//Send state to the server code
}



render(){
return (
    <div>
    <input type="text" onChange={this.updateInput}></input>
    <input type="submit" onClick={this.handleSubmit} ></input>
    </div>
  );
}
} 

//output
//Your input value is: x

最简单的方法是使用箭头函数

箭头函数的代码

export default class MyComponent extends React.Component {

onSubmit = (e) => {
    e.preventDefault();
    var title = this.title;
    console.log(title);
}

render(){
    return (
        ...
        <form className="form-horizontal">
            ...
            <input type="text" className="form-control" ref={(c) => this.title = c} name="title" />
            ...
        </form>
        ...
        <button type="button" onClick={this.onSubmit} className="btn">Save</button>
        ...
    );
}

};

给<input>一个唯一的id

<input id='title' ...>

然后使用标准的Web API在DOM中引用它

const title = document.getElementById('title').value

不需要在每次按键时不断更新React状态。只需在需要时获取值即可。

在功能组件中:-

export default function App(){

const [state, setState] = useState({
        value:'',
        show:''
    });

const handleChange = (e) => {
    setState({value: e.target.value})
}

const submit = () => {
    setState({show: state.value})
}

return(
        <>
            <form onSubmit={()=>submit()}>
                <input type="text" value={state.value} onChange={(e)=>handleChange(e)} />
                <input type="submit" />
            </form>
            <h2>{state.show}</h2>
        </>
)}