获取JSON并迭代react-native中的值

Question

我是新的反应本机,我试图简单地迭代一个示例json文件,但我收到错误undefined不是一个函数(评估'this.state.results.map')

我最初将状态设置为对象,所以不确定为什么我收到此错误.

这是JS:

import React, { Component } from 'react';
import { AppRegistry, ListView, Text, View, StyleSheet, TouchableHighlight } from 'react-native';

var REQUEST_URL = 'https://facebook.github.io/react-native/movies.json';

class WPReact extends Component {
  constructor(props) {
    super(props);
    this.state = {results: []};
  }
  componentDidMount() {
    this.fetchData();
  }
  fetchData() {
    fetch(REQUEST_URL)
      .then((response) => response.json())
      .then((responseData) => {
        this.setState({
          results : { responseData }
        });
      })
      .done();
  }
  render() {
    return this.renderJSON();
  }
  renderJSON() {
    contents = this.state.results.map((item) => {
      <View key={item.movies.title} style={ styles.container }>
        <Text style={styles.title}>
          {item.movies.title}
        </Text>
      </View>
     });
    return (
      <View style={styles.container}>
        {contents}
      </View>
    );
  }
}

var Dimensions = require('Dimensions');

var styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#FFFFFF',
  },
  textContainer: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
  },
  title: {
    fontSize: 30,
    textAlign: 'center',
    margin: 10,
  },
  text: {
    fontSize: 18,
    paddingLeft: 20,
    paddingRight: 20,
    textAlign: 'center',
    color: '#333333',
    marginBottom: 5,
  },
});

// App registration and rendering
AppRegistry.registerComponent('AwesomeProject', () => WPReact);

---

编辑

所以我已经编辑了renderJSON()并且还删除了responseData的大括号,因为它已经是一个对象了:

renderJSON() {

    console.log(this.state.results.description);
    contents = this.state.results.movies.map((item) => {
      <View key={item.title} style={ styles.container }>
        <Text style={styles.title}>
          {item.title}
        </Text>
      </View>
     });
    return (
      <View style={styles.container}>
        {contents}
      </View>
    );
  }

我添加了一个控制台日志,看看我是否可以输出一些数据,我可以看到描述.我正在使用的示例JSON是(来自react的演示):

{
  "title": "The Basics - Networking",
  "description": "Your app fetched this from a remote endpoint!",
  "movies": [
    { "title": "Star Wars", "releaseYear": "1977"},
    { "title": "Back to the Future", "releaseYear": "1985"},
    { "title": "The Matrix", "releaseYear": "1999"},
    { "title": "Inception", "releaseYear": "2010"},
    { "title": "Interstellar", "releaseYear": "2014"}
  ]
}

我可以记录描述和标题.但我仍然收到:ReactNativeJS: undefined is not an object (evaluating 'this.state.results.movies.map')

如果我尝试登录,console.log(this.state.results.movies[0].title)我会收到undefined is not an object (evaluating 'this.state.results.movies[0]')

fetchData() {
    fetch(REQUEST_URL)
      .then((response) => response.json())
      .then((responseData) => {
        console.log(responseData);
        this.setState({
          results : responseData
        });
      })
      .done();
  }

console.log(responseData)显示:

03-29 13:49:53.028  3062  4143 I ReactNativeJS: { title: 'The Basics - Networking',
03-29 13:49:53.028  3062  4143 I ReactNativeJS:   description: 'Your app fetched this from a remote endpoint!',
03-29 13:49:53.028  3062  4143 I ReactNativeJS:   movies: 
03-29 13:49:53.028  3062  4143 I ReactNativeJS:    [ { title: 'Star Wars', releaseYear: '1977' },
03-29 13:49:53.028  3062  4143 I ReactNativeJS:      { title: 'Back to the Future', releaseYear: '1985' },
03-29 13:49:53.028  3062  4143 I ReactNativeJS:      { title: 'The Matrix', releaseYear: '1999' },
03-29 13:49:53.028  3062  4143 I ReactNativeJS:      { title: 'Inception', releaseYear: '2010' },
03-29 13:49:53.028  3062  4143 I ReactNativeJS:      { title: 'Interstellar', releaseYear: '2014' } ] }

的console.log(this.state.results.movi​​es);

03-29 14:18:05.483  3062  4726 I ReactNativeJS: undefined
03-29 14:18:05.510  3062  4726 I ReactNativeJS: [ { title: 'Star Wars', releaseYear: '1977' },
03-29 14:18:05.510  3062  4726 I ReactNativeJS:   { title: 'Back to the Future', releaseYear: '1985' },
03-29 14:18:05.510  3062  4726 I ReactNativeJS:   { title: 'The Matrix', releaseYear: '1999' },
03-29 14:18:05.510  3062  4726 I ReactNativeJS:   { title: 'Inception', releaseYear: '2010' },
03-29 14:18:05.510  3062  4726 I ReactNativeJS:   { title: 'Interstellar', releaseYear: '2014' } ]

Answer 1

我看到您需要更改几件事。

首先，this.fetchData = this.fetchData.bind(this);在构造器中使用ES6时，需要绑定fetchData方法（寻找其他方法）。

其次，map应将其应用于this.state.results.movies此数组（在您的帖子之后）。this.state.results不是数组，是包含数组的对象。

import React, { Component } from 'react';
import { AppRegistry, ListView, Text, View, StyleSheet, TouchableHighlight } from 'react-native';

var REQUEST_URL = 'https://facebook.github.io/react-native/movies.json';

class WPReact extends Component {
  constructor(props) {
    super(props);

    this.state = {
      //Lets initialize results with the same struct we expect to receive from the api
      results: {
        title: '',
        description: '',
        movies: []
      }
    };
    //Using ES6 we need to bind methods to access 'this'
    this.fetchData = this.fetchData.bind(this);
  }

  componentDidMount() {
    this.fetchData();
  }

  fetchData() {
    fetch(REQUEST_URL)
      .then((response) => response.json())
      .then((responseData) => {
        this.setState({
          results: responseData
        });
      })
      .done();
  }

  render() {
    //this.state.results.movies is the array you have to iterate
    contents = this.state.results.movies.map((item) => {
      //We need to return the corresponding mapping for each item too.
      return (
          <View key={item.title} style={ styles.container }>
            <Text style={styles.title}>
              {item.title}
            </Text>
          </View>
        );
     });
    return (
      <View style={styles.container}>
        {contents}
      </View>
    );
  }
}

var Dimensions = require('Dimensions');

var styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#FFFFFF',
  },
  textContainer: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
  },
  title: {
    fontSize: 30,
    textAlign: 'center',
    margin: 10,
  },
  text: {
    fontSize: 18,
    paddingLeft: 20,
    paddingRight: 20,
    textAlign: 'center',
    color: '#333333',
    marginBottom: 5,
  },
});

// App registration and rendering
AppRegistry.registerComponent('AwesomeProject', () => WPReact);

让我知道它是否有效，我尚未测试过，但我会尽快进行。