react中怎么获取input的值

<input onChange={(e)=>this.inputChange(e)}/>

<button onClick={()=>this.getInputValue} >获取input的值</button>

inputChange(e){

alert(e.target.value)

this.setState({

username:e.target.value

})

}

getInputValue(){

alert(this.state.username)

}

<input ref='username' onChange={()=>this.inputChange()}/>

<button onClick={()=>this.getInputValue()} >获取input的值</button>

inputChange(){

//获取dom节点元素

//1.添加ref属性

//2.使用this.refs.username获取dom节点

let val=this.refs.username.value;

this.setState({

username:val

})

}

getInputValue(){

console.log(this.state.username)

}