区块链 Hello World -- 基于以太坊的投票Dapp

原创

wx5b3c8b549a762 2019-09-15 18:55:35 ©著作权

文章标签 blockchain ethereum 文章分类 区块链

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指路牌

以太坊
区块链
Dapp
以太坊hello world

环境

windows 10 64bit

参考博客

youclavier -- 以太坊投票Dapp教程

背景

准备接手一个IPFS+Ethereum的项目，先学习一下Ethereum，并尝试完成一个Hello World。

步骤

参考我另一片blog，安装nvm
安装node 9.11.1 并切换环境

nvm install 9.11.1
nvm use 9.11.1

创建一个新的工作目录，并在命令行索引到该路径
安装ganche-cli、web3、solc

npm install ganache-cli
npm install web3@0.20.1
npm install solc@0.4.21       //此处原博客没有版本，会安装高于0.4的版本，会导致后续编译smart contract编译失败

在安装了ganache-cli与web3时，由于教程版本问题会出现报错，但是不影响。

启动ganache-cli

node_modules\.bin\ganache-cli

ganache-cli启动后输出如下 6. 使用Solidity创建Smart Contract,命名为：Voting.sol

pragma solidity ^0.4.18; 

contract Voting {

  mapping (bytes32 => uint8) public votesReceived;
  bytes32[] public candidateList;

  function Voting(bytes32[] candidateNames) public {
    candidateList = candidateNames;
  }

  function totalVotesFor(bytes32 candidate) view public returns (uint8) {
    require(validCandidate(candidate));
    return votesReceived[candidate];
  }

  function voteForCandidate(bytes32 candidate) public {
    require(validCandidate(candidate));
    votesReceived[candidate]  += 1;
  }

  function validCandidate(bytes32 candidate) view public returns (bool) {
    for(uint i = 0; i < candidateList.length; i++) {
      if (candidateList[i] == candidate) {
        return true;
      }
    }
    return false;
   }}

启动node交互控制台，依次输入以下命令

> Web3 = require('web3')
> web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545"))
> web3.eth.accounts

输入以上最后一条命令后会获取Ganache创建的10个帐号，如下

> code = fs.readFileSync('Voting.sol').toString()
> solc = require('solc')
> compiledCode = solc.compile(code)

全部完成会得到如下截图的输出，表示smart contract编译成功 8.部署smart contract

> abi = JSON.parse(compiledCode.contracts[':Voting'].interface)
> VotingContract = web3.eth.contract(abi)
> byteCode = compiledCode.contracts[':Voting'].bytecode
> deployedContract = VotingContract.new(['James', 'Norah', 'Jones'],{data: byteCode, from: web3.eth.accounts[0], gas: 4700000})
> deployedContract.address

此时会获取address，记下来后续会用到

> contractInstance = VotingContract.at(deployedContract.address)

下载web3.js文件，下载后放在工作根目录下。

由cdn不知什么原因不可用，所以直接下载源文件，链接如下 web3.js 0.20.6
在根目录下创建index.html文件，并粘贴以下代码，需要在截图标出处，更换成第8步自己部署的smart contract的address

<!DOCTYPE html>
<html>
	<head>
		<title>DApp</title>
		<link href='https://fonts.googleapis.com/css?family=Open Sans:400,700' rel='stylesheet' type='text/css'>
		<link href='https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css' rel='stylesheet' type='text/css'>
	</head>
	<body class="container">
		Voting Application
		<div class="table-responsive">
			<table class="table table-bordered">
				<thead>
					<tr>
						<th>Candidate</th>
						<th>Votes</th>
					</tr>
				</thead>
				<tbody>
					<tr>
						<td>James</td>
						<td id="candidate-1"></td>
					</tr>
					<tr>
						<td>Norah</td>
						<td id="candidate-2"></td>
					</tr>
					<tr>
						<td>Jones</td>
						<td id="candidate-3"></td>
					</tr>
				</tbody>
			</table>
		</div>
		<input type="text" id="candidate" />
		<a rel="nofollow" href="#" onclick="voteForCandidate()" class="btn btn-primary">Vote</a>
	</body>
	
	<script src="web3.js"></script>
	<script src="https://code.jquery.com/jquery-3.1.1.slim.min.js"></script>
	<script language="javascript" type="text/javascript">
		web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545"));
		abi = JSON.parse('[{"constant":false,"inputs":[{"name":"candidate","type":"bytes32"}],"name":"totalVotesFor","outputs":[{"name":"","type":"uint8"}],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"candidate","type":"bytes32"}],"name":"validCandidate","outputs":[{"name":"","type":"bool"}],"payable":false,"type":"function"},{"constant":true,"inputs":[{"name":"","type":"bytes32"}],"name":"votesReceived","outputs":[{"name":"","type":"uint8"}],"payable":false,"type":"function"},{"constant":true,"inputs":[{"name":"x","type":"bytes32"}],"name":"bytes32ToString","outputs":[{"name":"","type":"string"}],"payable":false,"type":"function"},{"constant":true,"inputs":[{"name":"","type":"uint256"}],"name":"candidateList","outputs":[{"name":"","type":"bytes32"}],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"candidate","type":"bytes32"}],"name":"voteForCandidate","outputs":[],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"contractOwner","outputs":[{"name":"","type":"address"}],"payable":false,"type":"function"},{"inputs":[{"name":"candidateNames","type":"bytes32[]"}],"payable":false,"type":"constructor"}]')
		VotingContract = web3.eth.contract(abi);
		contractInstance = VotingContract.at('0x47f49b300eb86d972f91f103913376fb0a8e52e7');
		candidates = {"James": "candidate-1", "Norah": "candidate-2", "Jones": "candidate-3"}

		function voteForCandidate(candidate) {
			candidateName = $("#candidate").val();
			try {
				contractInstance.voteForCandidate(candidateName, {from: web3.eth.accounts[0]}, function() {
				let div_id = candidates[candidateName];
				$("#"+div_id).html(contractInstance.totalVotesFor.call(candidateName).toString());
			});
			} catch (err) {
			}
		}

		$(document).ready(function() {
			candidateNames = Object.keys(candidates);
			for (var i = 0; i < candidateNames.length; i++) {
				let name = candidateNames[i];
				let val = contractInstance.totalVotesFor.call(name).toString()
				$("#"+candidates[name]).html(val);
			}
		});
	</script>
</html>

更换address