ReactJS with Sockets Nested JSON parsing data issue

问题

I have a JSON file that has a structure like this "data.json"

{
    "Object1": {
        "name": "1",
        "rank": "2"
    },
    "Object2": {
        "name": "3",
        "rank": "4"
    }
}

and in my React code, I have my data to set my react state. I want to pass Object2 to a different component, but I can't seem to differentiate the data.

// import packages
import React, { Component } from "react";
import io from 'socket.io-client';

class App extends Component {
    constructor() {
        super();

        this.state = {
            data: null
        };
        this.socket = io('http://localhost:5000');

        // Binders
        this.updateState = this.updateState.bind(this);
    }

    componentDidMount() {
        this.socket.on('send data', this.updateState);
    }

    updateState(result) {
        this.setState({
            data: result
        });
    }

    render() {
        return (
            <p style={{ textAlign: "center" }}>
                {this.state.data}
            </p>
        );
    }
}

export default App;

When I try to reference something like this.state.data or this.state.data.Object1.name, it points to a null object. What am I doing wrong?

回答1:

I don't know so much about sockets but since you are setting the state after the first render, there isn't any data until componentDidMount finishes its job. So, you need conditional rendering.

const data = {
  "Object1": {
    "name": "1",
      "rank": "2"
  },
  "Object2": {
    "name": "3",
      "rank": "4"
  }
};

const fakeRequest = () => new Promise( resolve => 
  setTimeout( () => resolve(data), 2000 )
);

class App extends React.Component {
  state = {
    data: null,
  };

  componentDidMount() {
    fakeRequest().then( data => this.setState({data}));
  }

  render() {
    return <div>
      {!this.state.data ? "No data yet, wait 2 seconds." : this.state.data.Object1.name }
    </div>;
  }
}

ReactDOM.render(<App />, document.getElementById("root"));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="root"></div>

You can't use {this.state.data} since a React child can't be object. You need to use the values of this object.

来源：https://stackoverflow.com/questions/51868837/reactjs-with-sockets-nested-json-parsing-data-issue

标签

json

reactjs

setstate