在 React Native 中连接 REST API

Question

I am trying to learn how to connect APIs in React Native. I am using a sample API: https://reactnative.dev/movies.json

This is my code:

export default class App extends Component {
  constructor(props) {
    super(props);
    this.state = {
      loading: true,
      dataSource: [],
    };
  }
  componentDidMount() {
    return fetch("https://reactnative.dev/movies.json")
      .then((response) => response.json())
      .then((responseJson) => {
        this.setState({
          loading: false,
          dataSource: responseJson.movies,
        });
      })
      .catch((error) => console.log(error)); //to catch the errors if any
  }
  render() {
    if (this.state.isLoading) {
      return (
        <View style={styles.container}>
          <ActivityIndicator size="large" color="#0c9" />
        </View>
      );
    } else {
      let products = this.state.dataSource.map((val, key) => {
        return (
          <View key={key} style={styles.item}>
            <Text>{val}</Text>
          </View>
        );
      });
      return (
        <View style={styles.container}>
          <Text>{products.title}</Text>
        </View>
      );
    }
  }
}

The problem occurs with my "products" variable. In debug mode, I was able to see the key and value pairs which were correct from the API. However, the products array is populated with objects rather than strings which are structured like this: Object {$$typeof: Symbol(react.element), type: "RCTView", key: "0", …}

My code returns the following error: this.state.dataSource.map is not a function

EDIT: The answer below worked for the API I was using. Now I am trying a different API structured like this:

{"prods":
    {
    "86400":{"slug":"86400","url":"/86400"},
    "23andme":{"slug":"23andme","url":"/23andme"}
}}

I am having trouble with the mapping again. This returns an error:

return dataSource.map((val, key) => (
      <View key={key} style={styles.item}>
        <Text>{val.slug}</Text>
      </View>
    ));

Answer 1

First, there is a small typo in your example. In your component's constructor you specify a loading state variable, but in your render function you're using isLoading . Second, you're not mapping over your data correctly. It just looks like you need to specify what aspects of each movie you care about in your render function. JSX can't handle displaying a full javascript object which is what <Text>{val}</Text> ends up being in your code. There are a few ways you can fix this. It's very common to just map over your results and display them directly.

export default class App extends Component {
  constructor(props) {
    super(props);
    this.state = {
      loading: true,
      dataSource: []
    };
  }
  
  componentDidMount() {
    return fetch("https://reactnative.dev/movies.json")
      .then(response => response.json())
      .then(responseJson => {
        this.setState({
          loading: false,
          dataSource: responseJson.movies
        });
      })
      .catch(error => console.log(error));
  }

  render() {
    const { loading, dataSource } = this.state;

    if (loading) {
      return (
        <View style={styles.container}>
          <ActivityIndicator size="large" color="#0c9" />
        </View>
      );
    }

    return dataSource.map((movie, index) => (
      <View key={movie.id} style={styles.item}>
        <Text>{movie.title}</Text>
      </View>
    ));
  }
}

You could also pull this out to a renderMovies method, which might help since you are trying to display these in a styled container.

export default class App extends Component {
  constructor(props) {
    super(props);
    this.state = {
      loading: true,
      dataSource: []
    };
  }
  
  componentDidMount() {
    return fetch("https://reactnative.dev/movies.json")
      .then(response => response.json())
      .then(responseJson => {
        this.setState({
          loading: false,
          dataSource: responseJson.movies
        });
      })
      .catch(error => console.log(error));
  }

  renderMovies() {
    const { dataSource } = this.state;

    return dataSource.map((movie, index) => (
      <View key={movie.id} style={styles.item}>
        <Text>{movie.title}</Text>
      </View>
    ));
  }

  render() {
    const { loading } = this.state;

    if (loading) {
      return (
        <View style={styles.container}>
          <ActivityIndicator size="large" color="#0c9" />
        </View>
      );
    }

    return (
      <View style={styles.container}>
        {this.renderMovies()}
      </View>
    );
  }
}

Answer 2

I have used Object.values() to restructure the object into an array

  componentDidMount() {
    return fetch("https://reactnative.dev/movies.json")
      .then((response) => response.json())
      .then((responseJson) => {
        this.setState({
          loading: false,
          dataSource: Object.values(responseJson.movies),       //changed this
        });
      })
      .catch((error) => console.log(error));
  }

Answer 3

Try simple way. This code uses modern React practice and helps you to brush up your React skills in general. Give a try.

import React, {useState, useEffect} from 'react';
import { Text, View, StyleSheet } from 'react-native';
import axios from 'axios'; //for fetching data 

export default function App() {
 //React Hook for state
const [ data, setData ] = useState ([]);

//React Hook Instead Of ComponentDidMount
useEffect(() => {
 const fetchData = async () => {
   const result = await axios(
     "https://reactnative.dev/movies.json",
   );

   setData(result.data.movies);
 };

 fetchData();
 }, []);

return (
 <View>
   <Text>{JSON.stringify(data)}</Text>
 </View>
);
}