react 父组件调用子组件方法

<div id="correspond"></div>
<script type="text/babel">
    ///子组件
    var HelloMessage = React.createClass({
        childMethod: function(){
            alert("组件之间通信成功");
        },
        render: function() {
            return <div> <h1>Hello {this.props.name}</h1>  <button onClick={this.childMethod}>子组件</button></div>
        }
    });

    //父组件
    var ImDaddyComponent = React.createClass({
        getDS: function(){
            //调用组件进行通信
            this.refs.getSwordButton.childMethod();
        },
        render: function(){
            return (
                    <div>
                        <HelloMessage name="John" ref="getSwordButton" />
                        <button onClick={this.getDS}>父组件</button>
                    </div>
            );
        }
    });

    ReactDOM.render(
            <ImDaddyComponent  />,
            document.getElementById('correspond')
    );
</script>

这种方式在新版本react是走不通的，需要像下面这种操作

import React, {Component} from 'react';

export default class Parent extends Component {
    render() {
        return(
            <div>
                <Child onRef={this.onRef} />
                <button onClick={this.click} >click</button>
            </div>
        )
    }

    onRef = (ref) => {
        this.child = ref
    }

    click = (e) => {
        this.child.myName()
    }

}

class Child extends Component {
    componentDidMount(){
        this.props.onRef(this)
    }

    myName = () => alert('xiaohesong')

    render() {
        return ('woqu')
    }
}