props 可以把数据从父传给子，如果想要实现子传给父数据，可以把数据当成函数的参数传递给父组件，下面给一行代码揣摩：
class ParentCom extends React.Component{
constructor(props){
super(props)
this.state = {
childData:null
}
}
render(){
return (
<div>
<h1>子元素传递过来的数据：{this.state.childData}</h1>
<ChildCom setChildData={this.setChildData}/>
</div>
)
}
setChildData = (data) => {
this.setState({
childData:data
})
}
}
class ChildCom extends React.Component{
constructor(props){
super(props)
this.state = {
msg: "helloworld"
}
}
render(){
return (
<div>
<button onClick={this.sendData}>传递helloword给父元素</button>
</div>
)
}
sendData = () => {
this.props.setChildData(this.state.msg)
}
}
ReactDOM.render(
<ParentCom/>,
document.getElementById('root')
)