基于以太坊的区块链Hello World是怎样的
本文主要介绍"基于以太坊的区块链Hello World是如何的",希望能够解决您遇到有关问题,下面我们一起来看这篇 "基于以太坊的区块链Hello World是如何的" 文章。
环境
windows 10 64bit
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
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"> <h2>Voting Application</h2> <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。
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。
关于 "基于以太坊的区块链Hello World是如何的" 就介绍到这。希望大家多多支持编程宝库。
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