React Native TypeError：TypeError：undefined不是一个对象

Question

我决定重用我认为适用于引入第三方API的新应用程序的组件。有问题的可重用组件正在迭代this.props.data.map()，该组件在我的components/Swipe.js文件中评估为未定义：import React, { Component } from "react";import {  View,  Animated,  PanResponder,  Dimensions,  LayoutAnimation,  UIManager} from "react-native";const SCREEN_WIDTH = Dimensions.get("window").width;const SWIPE_THRESHOLD = 0.25 * SCREEN_WIDTH;const SWIPE_OUT_DURATION = 250;class Swipe extends Component {  static defaultProps = {    onSwipeRight: () => {},    onSwipeLeft: () => {}  };  constructor(props) {    super(props);    const position = new Animated.ValueXY();    const panResponder = PanResponder.create({      onStartShouldSetPanResponder: (event, gestureState) => true,      onPanResponderMove: (event, gestureState) => {        position.setValue({ x: gestureState.dx, y: gestureState.dy });      },      onPanResponderRelease: (event, gestureState) => {        if (gestureState.dx > SWIPE_THRESHOLD) {          this.forceSwipe("right");        } else if (gestureState.dx < -SWIPE_THRESHOLD) {          this.forceSwipe("left");        } else {          this.resetPosition();        }      }    });    this.state = { panResponder, position, index: 0 };  }  componentWillReceiveProps(nextProps) {    if (nextProps.data !== this.props.data) {      this.setState({ index: 0 });    }  }  componentWillUpdate() {    UIManager.setLayoutAnimationEnabledExperimental &&      UIManager.setLayoutAnimationEnabledExperimental(true);    LayoutAnimation.spring();  }  forceSwipe(direction) {    const x = direction === "right" ? SCREEN_WIDTH : -SCREEN_WIDTH;    Animated.timing(this.state.position, {      toValue: { x, y: 0 },      duration: SWIPE_OUT_DURATION    }).start(() => this.onSwipeComplete(direction));  }为什么会这样，因为我确实payload: data在动作创建者中找到了a ：

Answer 1

映射函数通常通过数组对象进行迭代。您正在尝试遍历非数组对象。因此，首先使用检查对象的类型，typeof(variable)然后使用函数。

Answer 2

看起来是什么帮助jobs_reducer从以下位置重构了我的文件：

import { FETCH_JOBS } from "../actions/types";

const INITIAL_STATE = {

  listing: []

};

export default function(state = INITIAL_STATE, action) {

  switch (action.type) {

    case FETCH_JOBS:

      return action.payload;

    default:

      return state;

  }

}

对此：

export default function(state = INITIAL_STATE, action) {

  switch (action.type) {

    case FETCH_JOBS:

      const { listings } = action.payload;

      return { ...state, listing: listings.listing };

    default:

      return state;

  }

}