如何从获取 api 中获取特定数据

Question

I am trying to get and show a specific data from api in a <Text> tag in my React Native app. What I'm trying to do is to show the name of second object from that api.

Here is my code:

class HomeSreen extends Component {
 constructor(props) {
   super(props);
   this.state = {
     dataSource: [],
   };
 }
 componentDidMount() {
   const request = new Request('http://jsonplaceholder.typicode.com/users');

   fetch(request)
     .then(response => response.json())
     .then(responseJson => {
       this.setState({
         dataSource: responseJson,
       });
     });
 }
 render() {
   return (
     <View>
       <Text>Home Screen</Text>
       <Text>{this.state.dataSource[1].name}</Text>
     </View>
   );
 }
}

And the API:

[

    {
        "id": 1,
        "name": "Leanne Graham",
        "username": "Bret",
        "email": "Sincere@april.biz",
        "address": {
            "street": "Kulas Light",
            "suite": "Apt. 556",
            "city": "Gwenborough",
            "zipcode": "92998-3874",
            "geo": {
                "lat": "-37.3159",
                "lng": "81.1496"
            }
        },
        "phone": "1-770-736-8031 x56442",
        "website": "hildegard.org",
        "company": {
            "name": "Romaguera-Crona",
            "catchPhrase": "Multi-layered client-server neural-net",
            "bs": "harness real-time e-markets"
        }
    },
    {
        "id": 2,
        "name": "Ervin Howell",
        "username": "Antonette",
        "email": "Shanna@melissa.tv",
        "address": {
            "street": "Victor Plains",
            "suite": "Suite 879",
            "city": "Wisokyburgh",
            "zipcode": "90566-7771",
            "geo": {
                "lat": "-43.9509",
                "lng": "-34.4618"
            }
        },
        "phone": "010-692-6593 x09125",
        "website": "anastasia.net",
        "company": {
            "name": "Deckow-Crist",
            "catchPhrase": "Proactive didactic contingency",
            "bs": "synergize scalable supply-chains"
        }
    },
.
.
.

But I can't get the data I need. Any help would be appreciated

Answer 1

these data requests asynchronously, so when the first render occurs, there is no data returned from the API.

class HomeSreen extends Component {
 constructor(props) {
   super(props);
   this.state = {
     dataSource: [],
   };
 }

 componentDidMount() {
   const request = new Request('http://jsonplaceholder.typicode.com/users');

   fetch(request)
     .then(response => response.json())
     .then(responseJson => {
       this.setState({
         dataSource: responseJson,
       });
     });
 }

 render() {
   return (
     <View>
       <Text>Home Screen</Text>
       {
         this.state.dataSource.length === 0 ?
           <Text>Waiting moment.</Text> :
           <Text>{this.state.dataSource[1].name}</Text>
       }

     </View>
   );
 }
}

Making these changes you can visualize the data you need.

Answer 2

If the problem is that your component isn't updating the that property after the request is complete it is because you are doing a 'shallow merge' on the dataSource Array so React isn't able to detect changes to the data. There are a few ways you can handle it:

1. Deep merge

fetch(request)
    .then(response => response.json())
    .then(responseJson => {
      this.setState(prevState => {
        return {
          ...prevState.dataSource,
          dataSource: responseJson.map((obj, i)=>{ return {...dataSource[i], ...obj}},
        }
      });
    });

https://reactjs.org/docs/optimizing-performance.html#shouldcomponentupdate-in-action

2. Pull the name property out to the top-level of you component state

class HomeSreen extends Component {
 constructor(props) {
   super(props);
   this.state = {
     dataSource: [],
     screenTitle
   };
 }
 componentDidMount() {
   const request = new Request('http://jsonplaceholder.typicode.com/users');

   fetch(request)
     .then(response => response.json())
     .then(responseJson => {
       this.setState({
         screenTitle: responseJson[1].name,
       });
     });
 }
 render() {
   return (
     <View>
       <Text>Home Screen</Text>
       <Text>{this.state.screenTitle}</Text>
     </View>
   );
 }
}