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一直在关注https://github.com/dappuniversity/starter_kit中的示例，但是当我尝试购买代币时，MetaMask 错误出现了。

$ truffle version Truffle v5.1.14 (core: 5.1.14) Solidity v0.5.16 (solc-js) Node v12.18.3 Web3.js v1.2.1 Ganache

本地运行自定义 RPC

我试图增加 GAS，但没有奏效。该项目的所有测试都通过了，所有合同都编译了，但我似乎无法让它发挥作用。任何帮助将不胜感激。谢谢

主.js

import React, { Component } from 'react';
import BuyForm from './BuyForm'
import SellForm from './SellForm'


class Main extends Component {
constructor(props) {
super(props)
this.state = {
  currentForm: 'buy'
}
}

render() {
  let content
  if(this.state.currentForm === 'buy'){
    content = <BuyForm
      ethBalance={this.props.ethBalance}
      tokenBalance={this.props.tokenBalance}
      buyTokens={this.props.buyTokens}
      />
  }else{
    content = <SellForm
    ethBalance={this.props.ethBalance}
    tokenBalance={this.props.tokenBalance}
    sellTokens={this.props.sellTokens}
     />
  }
return (
  <div id="content" className="mt-3">

    <div className="d-flex justify-content-between mb-3">
      <button
      className="btn btn-light"
      onClick={(event) => {
        this.setState({ currentForm: 'buy'})
      }}
      >
        Buy
      </button>
      <span className="text-muted">&lt; &nbsp; &gt;</span>
      <button className="btn btn-light"
      onClick={(event) => {
        this.setState({ currentForm: 'sell'})
      }}
      >
      Sell
      </button>
      </div>

    <div className="card mb-4">
      <div className="card-body">
        {content}


      </div>
      </div>

  </div>
);
}
}

  export default Main;

应用程序.js

import React, { Component } from 'react';
import Web3 from 'web3';
import Token from '../abis/Token.json'
import EthSwap from '../abis/EthSwap.json'
import Navbar from './Navbar'
import Main from './Main'
import './App.css';

class App extends Component {
async componentWillMount() {
await this.loadWeb3()
await this.loadBlockchainData()
}

async loadBlockchainData(){
  const web3 = window.web3

  const accounts = await web3.eth.getAccounts()
  this.setState({ account: accounts[0] })

  const ethBalance = await web3.eth.getBalance(this.state.account)
  this.setState({ ethBalance })

  //Load Token
const networkId = await web3.eth.net.getId()
const tokenData = Token.networks[networkId]
if(tokenData){
  const token = new web3.eth.Contract(Token.abi, tokenData.address)
  this.setState({token})
  let tokenBalance = await token.methods.balanceOf(this.state.account).call()
  this.setState({tokenBalance: tokenBalance.toString() })
}
 else {
 window.alert('Token contract not deployed to detected network')
 }



 //Load EthSwap
   const ethSwapData = EthSwap.networks[networkId]
   if(ethSwapData){
   const ethSwap = new web3.eth.Contract(EthSwap.abi, tokenData.address)
   this.setState({ethSwap})
   }
   else {
   window.alert('EthSwap contract not deployed to detected network')
     }
     this.setState({loading: false})
      }

     async loadWeb3() {
     if (window.ethereum) {
      window.web3 = new Web3(window.ethereum)
      await window.ethereum.enable()
    }
    else if (window.web3) {
      window.web3 = new Web3(window.web3.currentProvider)
      }
    else {
      window.alert('Non-Ethereum browser detected. You should consider trying MetaMask')
    }
}

buyTokens = (etherAmount) => {
  this.setState({ loading: true})
  this.state.ethSwap.methods.buyTokens().send({value: etherAmount, from: this.state.account}).on('transactionHash', (hash) => {
  this.setState({loading: false})
})
}

sellTokens = (tokenAmount) => {
  this.setState({ loading: true})
  this.state.token.methods.approve(this.state.ethSwap.address, tokenAmount)
  .send({ from: this.state.account}).on('transactionHash', (hash) => {
    this.state.ethSwap.methods.sellTokens(tokenAmount).send({ from: 
     this.state.account}).on('transactionHash',(hash) =>{
    this.setState({loading: false})

 })
 })
  }

constructor(props) {
super(props)
this.state = {
 account:'',
 token: {},
 ethSwap: {},
 ethBalance:'0',
 tokenBalance:'0',
 loading: false
 }
 }

  render() {
   let content
   if(this.state.loading){
    content = <p id="loader" className="text-center">Loading...</p>
}else {
  content = <Main
    ethBalance={this.state.ethBalance}
    tokenBalance={this.state.tokenBalance}
    buyTokens= {this.buyTokens}
    sellTokens={this.sellTokens}
  />

}
return (
  <div>
  <Navbar account={this.state.account} />
    <div className="container-fluid mt-5">
      <div className="row">
        <main role="main" className="col-lg-12 ml-auto mr-auto" style={{maxWidth: '600px'}}>
          <div className="content mr-auto ml-auto">
            <a
              href="http://www.dappuniversity.com/bootcamp"
              target="_blank"
              rel="noopener noreferrer"
            >

            </a>
            {content}

          </div>
        </main>
      </div>
    </div>
  </div>
);
}
}

export default App;

合同：

EthSwap.sol

pragma solidity ^0.5.0;

import "./Token.sol";

contract EthSwap {
  string public name = "EthSwap Instant Exchange";
  Token public token;
  uint public rate = 100;

  event TokensPurchased(
    address account,
    address token,
    uint  amount,
    uint  rate
    );

    event TokensSold(
      address account,
      address token,
      uint  amount,
      uint  rate
      );

  constructor(Token _token) public {
    token = _token;
  }

  function buyTokens() public payable {
    //Calculate the number of tokens to buy
    uint tokenAmount = msg.value * rate;

    //Require that EthSwap has enough tokens
    require(token.balanceOf(address(this)) >= tokenAmount);

    //Transer tokens to the user
    token.transfer(msg.sender, tokenAmount);

    //Emit on event
    emit TokensPurchased(msg.sender, address(token), tokenAmount, rate);
  }

    function sellTokens(uint _amount) public {
    //Uswer can't sell more tokens than they have
    require(token.balanceOf(msg.sender) >= _amount);

    // Calculate the amount of Ether to redeem
    uint etherAmount = _amount / rate;

    //Require that EthSwap has enough ether
    require(address(this).balance >= etherAmount);

    //Perform sale
    token.transferFrom(msg.sender, address(this), _amount);
    msg.sender.transfer(etherAmount);

    //Emit on event
    emit TokensSold(msg.sender, address(token), _amount, rate);

    }
}

令牌.sol

pragma solidity ^0.5.0;

contract Token {
    string  public name = "DApp Token";
    string  public symbol = "DAPP";
    uint256 public totalSupply = 1000000000000000000000000; // 1 million tokens
    uint8   public decimals = 18;

    event Transfer(
        address indexed _from,
        address indexed _to,
        uint256 _value
    );

    event Approval(
        address indexed _owner,
        address indexed _spender,
        uint256 _value
    );

    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) public allowance;

    constructor() public {
        balanceOf[msg.sender] = totalSupply;
    }

    function transfer(address _to, uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);
        balanceOf[msg.sender] -= _value;
        balanceOf[_to] += _value;
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= balanceOf[_from]);
        require(_value <= allowance[_from][msg.sender]);
        balanceOf[_from] -= _value;
        balanceOf[_to] += _value;
        allowance[_from][msg.sender] -= _value;
        emit Transfer(_from, _to, _value);
        return true;
    }
}
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