javascript - 如何在渲染中的 react js中传递数组

Question

我正在使用 React JS 开发一个 IPFS-Ethereum 应用程序，我将在其中上传一个 XML 文件并对其进行解析。我在将解析的数据显示为表中的数组时遇到问题。它仅显示数组中的最后一个元素。

This is the code used for parsing, in console it is showing the two data in the console which is parsed. But in Table it is showing only the last element. I tried using this this.liItem[i]/this.liItem[0] but it is throwing undefined error.

var request = new Request(`https://gateway.ipfs.io/ipfs/${this.state.ipfsHash}`);
fetch(request).then((results) => {
  // results returns XML. lets cast this to a string, then create
  // a new DOM object out of it!
  results
    .text()
    .then((str) => {
      this.state.responseDoc = new DOMParser().parseFromString(str, 'application/xml');
      console.log(this.state.responseDoc);

      this.state.listItem = this.state.responseDoc.getElementsByTagName('Name');
      // console.log(listItem);
      for (this.i = 0; this.i < this.state.listItem.length; this.i++) {
        this.liItem = this.state.responseDoc.getElementsByTagName('Name')[this.i].textContent;
        this.setState({
          liItem: this.state.liItem
        });
        console.log(this.liItem);
      }
    })

这是表中用来显示数组数据的行{this.liItem}。 ( picture link )

这是我的 App.js 文件。

从 'react-bootstrap' 导入 {Table, Grid, Button, Form}; import React, { Component } from 'react'; 导入'./App.css'； 从 './web3' 导入 web3； 从 './ipfs' 导入 ipfs； 从“./storehash”导入 storehash；

class App extends Component {
  state = {
    ipfsHash:null,
    buffer:'',
    ethAddress:'',
    blockNumber:'',
    transactionHash:'',
    gasUsed:'',
    txReceipt: '',
    responseDoc:'',
    listItem:'',
    i:'',
    liItem:[]
  };


  captureFile =(event) => {
    event.stopPropagation()
    event.preventDefault()
    const file = event.target.files[0]
    let reader = new window.FileReader()
    reader.readAsArrayBuffer(file)
    reader.onloadend = () => this.convertToBuffer(reader)    
  };

  convertToBuffer = async(reader) => {
    //file is converted to a buffer to prepare for uploading to IPFS
    const buffer = await Buffer.from(reader.result);
    //set this buffer -using es6 syntax
    this.setState({buffer});
  };

  onClick = async () => {
  try{
      this.setState({blockNumber:"waiting.."});
      this.setState({gasUsed:"waiting..."});

      // get Transaction Receipt in console on click
      // See: https://web3js.readthedocs.io/en/1.0/web3- eth.html#gettransactionreceipt
      await web3.eth.getTransactionReceipt(this.state.transactionHash, (err, txReceipt)=>{
      console.log(err,txReceipt);
        this.setState({txReceipt});
      }); //await for getTransactionReceipt

      await this.setState({blockNumber: this.state.txReceipt.blockNumber});
      await this.setState({gasUsed: this.state.txReceipt.gasUsed});    
    } //try
    catch(error){
    console.log(error);
    } //catch


    var request = new Request(`https://gateway.ipfs.io/ipfs/${this.state.ipfsHash}`);
    fetch(request).then((results) => {
      // results returns XML. lets cast this to a string, then create
      // a new DOM object out of it!
      results
      .text()
      .then(( str ) => {
        this.state.responseDoc = new DOMParser().parseFromString(str, 'application/xml');
        console.log(this.state.responseDoc);

        this.state.listItem  = this.state.responseDoc.getElementsByTagName('Name');
                // console.log(listItem);
        for (this.i=0; this.i<this.state.listItem.length; this.i++){
          this.liItem = this.state.responseDoc.getElementsByTagName('Name')[this.i].textContent;
          this.setState({liItem: this.state.liItem});
          console.log(this.liItem);
        }
      })
    });
  } //onClick

  onSubmit = async (event) => {
    event.preventDefault();

    //bring in user's metamask account address
    const accounts = await web3.eth.getAccounts();

    console.log('Sending from Metamask account: ' + accounts[0]);

    //obtain contract address from storehash.js
    const ethAddress= await storehash.options.address;
    this.setState({ethAddress});

    //save document to IPFS,return its hash#, and set hash# to state
    //https://github.com/ipfs/interface-ipfs-core/blob/master/SPEC/FILES.md#add 
    await ipfs.add(this.state.buffer, (err, ipfsHash) => {
      console.log(err,ipfsHash);
      //setState by setting ipfsHash to ipfsHash[0].hash 
      this.setState({ ipfsHash:ipfsHash[0].hash });


      // call Ethereum contract method "sendHash" and .send IPFS hash to etheruem contract 
      //return the transaction hash from the ethereum contract
      //see, this https://web3js.readthedocs.io/en/1.0/web3-eth-contract.html#methods-mymethod-send

      storehash.methods.sendHash(this.state.ipfsHash).send({
          from: accounts[0] 
        }, (error, transactionHash) => {
          console.log(transactionHash);
          this.setState({transactionHash});
        }

      ); //storehash 
    }) //await ipfs.add
  }; //onSubmit 


  render() {

    return (
      <div className="App">
        <header className="App-header">
          <h1>
            {" "}
            Ethereum and InterPlanetary File System(IPFS) with Create React App
          </h1>
        </header>
        <hr />

        <Grid>
          <h3> Choose file to send to IPFS </h3>
          <Form onSubmit={this.onSubmit}>
            <input type="file" onChange={this.captureFile} />
            <Button bsStyle="primary" type="submit">
              Send it
            </Button>
          </Form>
          <br />

          <img
            src={`https://ipfs.io/ipfs/${this.state.ipfsHash}`}
            alt=""
            style={{ height: 200 }}
          />

          <hr />
          <Button onClick={this.onClick}> Get Transaction Receipt </Button>
          <Table bordered responsive>
            <thead>
              <tr>
                <th>Tx Receipt Category</th>
                <th>Values</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td>IPFS Hash # stored on Eth Contract</td>
                <td>{this.state.ipfsHash}</td>
              </tr>
              <tr>
                <td>Ethereum Contract Address</td>
                <td>{this.state.ethAddress}</td>
              </tr>
              <tr>
                <td>Tx Hash # </td>
                <td>{this.state.transactionHash}</td>
              </tr>
              <tr>
                <td>Block Number # </td>
                <td>{this.state.blockNumber}</td>
              </tr>
              <tr>
                <td>Gas Used</td>
                <td>{this.state.gasUsed}</td>
              </tr>
              <tr>
                <td>XML</td>
                <td>{this.liItem}</td>
              </tr>
            </tbody>
          </Table>
        </Grid>
      </div>
    );
    //render
  }
}

export default App;

我希望你们能理解我的问题并给我一个解决方案。谢谢你

Answer 1

试试这个:

<tr>
    <td>XML</td>
    <td>{this.liItem.map((value, index) => {
        <p key={index}>{value}</p>
    })}</td>
</tr>

有了它，您应该将所有条目放在单独的行中(因为 p 是 w=100%)