使用ref报错，addComponentAsRefTo(...): Only a ReactOwner can have refs.

(1)addComponentAsRefTo(...): Only a ReactOwner can have refs. You might be adding a ref to a component that was not created inside a component's `render` method, or you have multiple copies of React loaded (details: https://fb.me/react-refs-must-have-owner).

错误原因：没有将ref写成回调形式，出现报错；

import ReactDOM from 'react-dom';

handlerAddClick(e){
        e.preventDefault();//阻止默认事件
        let item = {};//单挑数据
        let addForm = ReactDOM.findDOMNode(this.addForm);
        
        
    }
    render(){
        return(
            <div ref={(ref)=>this.addForm = ref }>
            <form  className="footerAddd"></form>

(2)再配合ref使用findDOMNode错误

Uncaught TypeError: __WEBPACK_IMPORTED_MODULE_0_react___default.a.findDOMNode is not a function

使用15.0以后的版本需要引入ReactDOM,如上面的所示。