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nvmnvm install 9.11.1 nvm use 9.11.1npm 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。
- 安装node 9.11.1 并切换环境
- 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
- 启动ganache-clinode_modules.binganache-cli
ganache-cli启动后输出如下
6. 使用Solidity创建Smart Contract,命名为：Voting.solpragma 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;
}}> 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 - 启动node交互控制台，依次输入以下命令
> 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
代码语言：txt复制> 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"> <h1>Voting Application</h1> <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 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> ``` 
- 在浏览器打开index.html,输入Candidate中的人名后，点击Vote即可投票，投票后效果如下
每次点击投票，也都会生成一个新的区块，效果如下。
后记
以上步骤就完成了一个基于Ethereum的投票Dapp的完整搭建流程，整合个补全后步骤应该不会有坑的可以顺利搭建完成。
就像“hello world”的字面意思一样，0-1的过程是最艰难的，但是开了头，剩下的1-n也就会顺畅不少。
