this.setState 未定义 [英] this.setState is undefined

问题描述

我一直看到答案说使用 => 或 .bind(this) 但这些解决方案都不起作用.

import React, { Component } from 'react';import { View, Text, TextInput, StyleSheet } from 'react-native';导出默认类 MyWeatherApp 扩展组件 {构造函数(道具){超级(道具)；this.state = {};}getInitialState() {返回 {压缩: ''，预测:空，};}_handleTextChange(事件){var zip = event.nativeEvent.text;this.setState({zip: zip});}

解决方案:

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

解决方案

当您使用 ES2015 类语法extend React.Component 时，您需要将动作处理程序绑定到你的班级背景.

试试这个:onChange={e =>_handleTextChange(e)}

通常，最好不要在 render 中使用箭头函数或 bind 方法，因为它会在任何 render 上生成函数的新副本称呼.将函数声明移至类构造函数.

我个人更喜欢在这种情况下使用箭头函数作为类属性

class MyClass 扩展 React.Component {handleClick = () =>{//你的逻辑};使成为() {返回 (<button onClick={this.handleClick}>点击我</button>);}}

它不是 ES2015 规范的一部分，但 babel stage-0 preset 支持这种语法>

您可以在这篇文章

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');
}

解决方案

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

这篇关于this.setState 未定义的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！