reactjs - this.setState is undefined

Question

I keep seeing answers that say to use => or .bind(this) but neither of those solutions worked.

import React, { Component } from 'react';
import { View, Text, TextInput, StyleSheet } from 'react-native';

export default class MyWeatherApp extends Component {
  constructor(props) {
  super(props);

  this.state = {};
}

getInitialState() {
  return {
    zip: '',
    forecast: null,
  };
}

_handleTextChange(event) {
  var zip = event.nativeEvent.text;
  this.setState({zip: zip});
}

Solution:

_handleTextChange = (event) => {
  var zip = event.nativeEvent.text;
  this.setState({zip: zip});
  alert('click');
}

question from:https://stackoverflow.com/questions/39210971/this-setstate-is-undefined

Answer 1

When you extend React.Component with ES2015 class syntax you need to bind your action handlers to a context of your class.

Try this: onChange={e => _handleTextChange(e)}

Generally, it's better not to use arrow functions or bind methods inside render as it generates a new copy of the function on any render call. Move function declaration to the class constructor.

I personally prefer to use arrow functions as class properties in this case

class MyClass extends React.Component {

  handleClick = () => {
    // your logic
  };

  render() {
    return (
      <button onClick={this.handleClick}>Click me</button>
    );
  }
}

It's not a part of ES2015 specification but babel stage-0 preset supports this syntax

You can read more about context binding in React in this article