如何在React Native中循环数组

Question

RSS feed被解析为一个数组，但是问题是，该数组不会循环，它仅显示一项。如何循环我的Feeds数组？

这是我的代码，我使用react-native-rss-parser（https://www.npmjs.com/package/react-native-rss-parser）：

class TNScreens extends React.Component { 
  state = {
    feed: [],
    title: []
  };

  componentDidMount() {
    return fetch("https://vnexpress.net/rss/tin-moi-nhat.rss")
      .then(response => response.text())
      .then(responseData => rssParser.parse(responseData))
      .then(rss => {
        for (let i = 0; i < rss.items.length; i++) {
          this.setState(prevState => ({
            ...prevState,
            feed: rss.items[i],
            title: rss.items[i].title
          }));
        }
      });
  }

  render() {
    const Feeds = ([
      {
        pic: {uri: ''},
        title: Object.keys(this.state.title).map(i => this.state.title[i])
      }
    ]);

    return (
      <SafeAreaView>
        <ScrollView>
          <Text h2 h2Style={styles.h2Style}>
            Trang nhất
          </Text>
          <Text h4 h4Style={styles.h4Style}>
            Cập nhật siêu nhanh
          </Text>
          <View>

            {Feeds.map(({ pic, title }) => (

              <Tile
                imageSrc={pic}
                height={200}
                activeOpacity={0.9}
                title={title}
                titleNumberOfLines={1}
                titleStyle={styles.title}
                featured
                key={title}
              />
            ))}
          </View>
        </ScrollView>
      </SafeAreaView>
    );
  }
}

export default TNScreen;

UPDATE

console.log（rss）结果：

Object {
  "authors": Array [],
  "categories": Array [],
  "copyright": undefined,
  "description": "VnExpress RSS",
  "image": Object {
    "description": undefined,
    "height": undefined,
    "title": "Tin nhanh VnExpress - Đọc báo, tin tức online 24h",
    "url": "https://s.vnecdn.net/vnexpress/i/v20/logos/vne_logo_rss.png",
    "width": undefined,
  },
  "items": Array [],
  "itunes": Object {
    "authors": Array [],
    "block": undefined,
    "categories": Array [],
    "complete": undefined,
    "explicit": undefined,
    "image": undefined,
    "newFeedUrl": undefined,
    "owner": Object {
      "email": undefined,
      "name": undefined,
    },
    "subtitle": undefined,
    "summary": undefined,
  },
  "language": undefined,
  "lastPublished": "Sat, 30 Nov 2019 21:28:12 +0700",
  "lastUpdated": undefined,
  "links": Array [
    Object {
      "rel": "",
      "url": "https://vnexpress.net/rss/tin-moi-nhat.rss",
    },
  ],
  "title": "Tin mới nhất - VnExpress RSS",
  "type": "rss-v2",
}

Answer 1

for循环中的代码中存在问题，您只是用一个值替换状态，而不是复制前一个状态。您将必须

this.setState(prevState => ({
        ...prevState,
        feed: [...prevState.feed, rss.items[i]],
        title: [...prevState, rss.items[i].title]
}));

但这不是最佳实践，因为在每次迭代中您的渲染都会重新渲染，因此最佳实践是

const feeds = rss.items.map(item => item);
const titles = rss.items.map(item => item.title);

this.setState({ feed: feeds, title:titles });

Answer 2

您的this.state.x仅保存一项，将代码更改为以下内容：并且您还应该更改get Data方法，请不要在循环中使用setState

componentDidMount() {
    return fetch("https://vnexpress.net/rss/tin-moi-nhat.rss")
      .then(response => response.text())
      .then(responseData => rssParser.parse(responseData))
      .then(rss => {
        let copyRess = []
        let copyTitle = []
        for (let i = 0; i < rss.items.length; i++) {
          copyRess.push(rss.items[i]);
          copyTitle.push(rss.items[i].title)
        }
        this.setState(prevState => ({
            ...prevState,
            feed: copuRess,
            title: copyTitle
          }));
      });
  }

render() {
    const Feeds = []
    this.state.title.map(element => {
          Feeds.push({pic:"",title:element})
    })

    ....