React Native this.'function' 不是函数 [英] React Native this.'function' is not a function

问题描述

我正在学习 React Native 和 Redux，这里有许多类似的问题，但我很难解决我的问题.

I'm in the middle of learning React Native and Redux and there are many similar problems to mine in here but I'm having a hard time to relate with my problem.

当我在另一个方法中调用一个方法时，它一直向我返回 this.'some function' 不是一个函数，我真的不知道该怎么做.

When I invoke a method in another method, it keeps returning me this.'some function' is not a function and I really have no idea what to do.

这是我的一些代码..

import React, { Component } from 'react';
import { Text, StyleSheet, ScrollView } from 'react-native';
import { connect } from 'react-redux';
import Panel from '../components/panel';

class Orders extends Component {
    displayItems(obj) {
        console.log('itemArr', obj);
        return obj.items.map(function(item){
           return (<Text>{item.quantity + ' ' + item.name}</Text>)
        });
    }

    renderContents() {
        console.log('orders', this.props.orders);
        if (!this.props.orders) {
            return <Text>Loading...</Text>;
        }
        return this.props.orders.map(function(order) {  
                return (
                    <Panel title={order.id} key={order.id}>
                        <Text>
                            Item: {this.displayItems(order)}{'\n'}

                        </Text>
                    </Panel>
                );
        });
    }

    render() {
        return(
            <ScrollView style={styles.container}>
                {this.renderContents()}
            </ScrollView>
        );
    }
}

我不知道为什么 render 方法中的函数不会导致任何错误，但我的 renderContents 方法中的函数会导致任何错误.

I'm not sure why the function inside of render method does not cause any error but the function invoke in my renderContents method does.

我感谢任何解决此问题的建议.

I appreciate any advice to get around this problem.

推荐答案

这是一个绑定问题.JavaScript 中的函数有自己的 this 上下文，除非另有明确说明，所以当你这样做时

This is a binding issue. Functions in JavaScript have their own this context unless explicitly told otherwise, so when you do

return this.props.orders.map(function(order) {  
  return (
    <Panel title={order.id} key={order.id}>
      <Text>Item: {this.displayItems(order)}{'\n'}</Text>
    </Panel>);
});

this 不是指向你的类，而是指向函数本身.只需执行以下操作

this is not pointing to your class, but to the function itself. Just do the following

return this.props.orders.map((order) => {  
  return (
    <Panel title={order.id} key={order.id}>
      <Text>Item: {this.displayItems(order)}{'\n'}</Text>
    </Panel>);
});

箭头函数没有自己的上下文，所以这应该适合你.你也可以调用 bind，但我认为箭头函数的解决方案更简单.

Arrow functions do not have their own context, so this should work for you. You could also call bind, but I think the arrow function solution is simpler.

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