区块链 Hello World -- 基于以太坊的投票Dapp

原创

HaythamXu

修改于 2019-09-10 17:01:41

7080

修改于 2019-09-10 17:01:41

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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\.bin\ganache-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

> 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> ``` ![更换address](https://user-images.githubusercontent.com/37465243/64078738-f976e400-cd10-11e9-82ef-20468a8e6ba5.png)