ソフトウェアエンジニアの技術ブログ：Software engineer tech blog

pragma solidity ^0.8.0;

interface IERC20 {
    function transfer(address to, uint256 amount) external returns (bool);
    function transferFrom(address from, address to, uint256 amount) external returns (bool);
}

contract SimpleSwap {
    address public owner;
    IERC20 public token;
    uint256 public rate;

    constructor(address _tokenAddress, uint256 _rate) {
        owner = msg.sender;
        token = IERC20(_tokenAddress);
        rate = _rate;
    }

    receive() external payable {
        uint256 tokenAmount = msg.value * rate;
        require(token.transfer(msg.sender, tokenAmount), "Token transfer failed");
    }

    function swapTokenForETH(uint256 tokenAmount) external {
        uint256 ethAmount = tokenAmount / rate;
        require(address(this).balance >= ethAmount, "Not enough ETH in contract");

        require(token.transferFrom(msg.sender, address(this), tokenAmount), "Token transfer failed");

        (bool success, ) = msg.sender.call{value: ethAmount}("");
        require(success, "ETH transfer failed");
    }

    function withdrawETH() external {
        require(msg.sender == owner, "Not owner");
        payable(owner).transfer(address(this).balance);
    }

    function withdrawTokens() external {
        require(msg.sender == owner, "Not owner");
        uint256 balance = tokenBalance();
        require(token.transfer(owner, balance), "Token withdrawal failed");
    }

    function tokenBalance() public view returns (uint256) {
        return token.balanceOf(address(this));
    }
}

sendではなく、recipient.callで送信してますね。

pragma solidity ^0.8.0;

constract ConditionTransfer {
    address public owner;
    address payable public recipient;
    uint256 public unlockTime;

    constructor(address payable _recipient, uint256 _unlockTime) {
        owner = msg.sender;
        recipient = _recipient;
        unlockTime = _unlockTime;
    }

    receive() external payable {}

    function release() external {
        require(msg.sender == owner, "Only owner can release funds");
        require(block.timestamp >= unlockTime, "Funds are locked");

        uint256 amount = address(this).balance;
        require(amount > 0, "No funds to send");

        (bool success, ) = recipient.call{value: amount}("");
        require(success, "Transfer failed");
    }
}

単純にアドレスに保存するだけであれば、mapping(address => Data) accounts;とすれば良さそう。
ただし、この場合は、商品ごとにアドレスを持っていないといけない。
緯度経度やstatusの管理は、フロントエンド側(React)で実装か…
memoryとstorageの仕様詳細が欲しいところ。。。

pragma solidity ^0.8.17;

contract Traceability {

    struct Data {
        uint256 id;
        string name;
        string latitude;
        string longitude;
        string status;
    }

    address[] public users;

    mapping(address => Data) accounts;

    function registerAccount(uint256 _id, string memory _name, string memory latitude, string memory longitude, string memory status)
        public 
        returns (bool)
    {
        accounts[msg.sender].id = _id;
        accounts[msg.sender].name = _name;
        accounts[msg.sender].latitude = latitude;
        accounts[msg.sender].longitude = longitude;
        accounts[msg.sender].status = status;
        
        users.push(msg.sender);
        return true;
    }

    function ViewAccount(address user) public view returns (uint256, string memory, string memory, string memory, string memory) {
        uint256 _id = accounts[user].id;
        string memory _name = accounts[user].name;
        string memory _latitude = accounts[user].latitude;
        string memory _longitude = accounts[user].longitude;
        string memory _status = accounts[user].status;

        return (_id, _name, _latitude, _longitude, _status);
    }

}

ethの受け取り

pragma solidity ^0.8.17;

contract RecvEther {
    address public sender;

    uint public recvEther;

    function () payable {
        sender = msg.sender;
        recvEther += msg.value;
    }
}

memoryは処理中のみ保存し、storageは処理後、ブロックチェーンに保存される。

pragma solidity ^0.8.17;

contract Register {
    struct Data {
        string name;
        uint256 age;
        string hobby;
    }

    // 全ユーザのアドレスを保存
    address[] public users;

    mapping(address => Data) accounts;

    function registerAccount(string memory _name, uint256 _age, string memory _hobby) 
        public 
        returns (bool)
    {
        if (!isUserExist(msg.sender)) {
          users.push(msg.sender);
        }
        // msg.sender はトランザクション送信者
        accounts[msg.sender].name = _name;
        accounts[msg.sender].age = _age;
        accounts[msg.sender].hobby = _hobby;
        return true;
    }

    function isUserExist(address user) public view returns (bool) {
        for (uint256 i = 0; i < users.length; i++) {
            if (users[i] == user) {
                return true;
            }
        }
        return false;
    }

    function ViewAccount(address user) public view returns (string memory, uint256, string memory) {
        string memory _name = accounts[user].name;
        uint256 _age = accounts[user].age;
        string memory _hobby = accounts[user].hobby;

        return (_name, _age, _hobby);
    }
}

remixでデプロイのテストができる

metamaskアカウントでsepoliaにdeployする
https://sepolia.etherscan.io/

フロントエンド

import React from "react";
import Resister from "./Register.json";
import getWeb3 from "./getWeb3";
// import "./App.css";
class App extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      web3: null,
      accounts: null,
      contract: null,
      name: null,
      age: null,
      hobby: null,
      address: "",
      outputName: null,
      outputAge: null,
      outputHobby: null,
    };
  }

  componentDidMount = async () => {
    try {
      const web3 = await getWeb3();

      const accounts = await web3.eth.getAccounts();
      const networkId = await web3.eth.net.getId();
      const deployedNetwork = Resister.networks[networkId];
      const instance = new web3.eth.Contract(
        Resister.abi,
        deployedNetwork && deployedNetwork.address
      );

      this.setState({ web3, accounts, contract: instance });
    } catch (error) {
      alert(
        `Failed to load web3, accounts, or contract. Check console for details.`
      );
      console.error(error);
    }

    const { accounts } = this.state;
    console.log(accounts);
  };

  // アカウント情報の登録
  writeRecord = async () => {
    const { accounts, contract, name, age, hobby } = this.state;
    const result = await contract.methods.registerAccount(name, age, hobby).send({
      from: accounts[0],
    });
    console.log(result);

    if (result.status === true) {
      alert('会員登録が完了しました。');
    }
  };

  // アカウント情報の読み込み
  viewRecord = async () => {
    const { contract, accounts } = this.state;
    console.log(contract);

    const result = await contract.methods.viewAccount(accounts[0]).call();
    console.log(result);

    const outputName = result[0];
    const outputAge = result[1];
    const outputHobby = result[2];
    this.setState({ outputName, outputAge, outputHobby });
  };

  handleChange = (name) => (event) => {
    this.setState({ [name]: event.target.value });
  };

  render() {
    return (
      <div className="App">
        <br />
        <form>
          <div>
            <label>氏名：</label>
            <input
              onChange={this.handleChange("name")} />
          </div>

          <div>
            <label>年齢：</label>
            <input
              onChange={this.handleChange("age")} />
          </div>

          <div>
            <label>趣味：</label>
            <input
              onChange={this.handleChange("hobby")} />
          </div>

          <button type='button' onClick={this.writeRecord}>
            会員登録
          </button>
        </form>

        <br />
        <br />

        <form>
          <label>検索したいアドレスを入力してください。</label>
          <input onChange={this.handleChange("address")} />

          <button type='button' onClick={this.viewRecord}>
            検索
            </button>
        </form>

        <br />
        <br />

        {this.state.outputName ? <p>氏名: {this.state.outputName}</p> : <p></p>}
        {this.state.outputAge ? <p>年齢: {this.state.outputAge}</p> : <p></p>}
        {this.state.outputHobby ? <p>趣味: {this.state.outputHobby}</p> : <p></p>}

      </div>

    );
  }
}

export default App;

ちょっと記事が古いので期待通りに動かないが、