• When we bind a method to a DOM element, for example:<input type="text" ref="myinput" accept = "image/*" onChange = {this.selectFile} />
  • Uncaught TypeError: Cannot read property ‘refs’ of null or undefind

chestnut

import React from 'react';
import $ from 'jquery'
import '.. /app.scss';

export default class MyForm extends React.Component {
    submitHandler (event) {
        event.preventDefault();
        console.log(this.refs.helloTo);
        var helloTo = this.refs.helloTo.value;
        alert(helloTo);
    }
    render () {
        return (
            <form onSubmit={this.submitHandler}>
                  <input ref='helloTo' type='text' defaultValue='Hello World! ' />
                  <button type='submit'>Speak</button>
              </form>)}}Copy the code

Bind ={this.handleclick};};};};};};};};};};};}; The solution is to bind(this) when the function is called, so that this refers to the currently instantiated object regardless of how the event handler is passed.

To solve

  • There are four solutions
  1. In ES6, you can bind an instance of the current component (or class) directly to a function in a constructor.
  2. Bind this to the method call as follows:<input type="file" ref="myinput" accept = "image/*" onChange = {this.selectFile.bind(this)} />
  3. At the end of the method, bind (this) :
SubmitHandler () {console.log (1The bind ()}this)
Copy the code
  1. Use the ES6 arrow functionmyfn = () =>{ console.log(this.refs.can) }

Recommended to use the arrow function, because recently changed to react, did not see much to cli to fight, encountered some small problems recorded here