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如何编写智能合约(Smart Contract)- 从零构建和部署去中心化投票App

课程目标

  1. 了解区块链智能合约
  2. 学会搭建智能合约开发环境
  3. 学会如何编译智能合约
  4. 学会如何将智能合约部署到区块链
  5. 学会如何通过WebApp和智能合约尽心互动
  6. 掌握DApp(去中心化App)的整个开发部署流程
  7. 掌握去中心化在实战产品中应用的重大意义

项目效果图

如何编写智能合约(Smart Contract)- 从零构建和部署去中心化投票App

编辑器选择

理论上讲任何编辑器都可以编写Solidity合约代码,比如:WebStorm,VSCode,Sublime,等等。我选择的是Atom,没有任何理由,因为Atom轻量并且界面漂亮。

  • 移步https://atom.io/地址,下载安装Atom。
  • autocomplete-solidity代码自动补齐

如何编写智能合约(Smart Contract)- 从零构建和部署去中心化投票App

  • linter-soliumlinter-solidity代码错误检查
  • language-ethereum支持Solidity代码高亮以及Solidity代码片段

如何编写智能合约(Smart Contract)- 从零构建和部署去中心化投票App

安装所需工具

首先开发机上必须装好Node.js,再使用以下命令安装所需的工具:

$ npm install -g ethereumjs-testrpc truffle 

liyuechun:~ yuechunli$ npm install -g ethereumjs-testrpc truffle /usr/local/bin/testrpc -> /usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js /usr/local/bin/truffle -> /usr/local/lib/node_modules/truffle/build/cli.bundled.js + truffle@3.4.9 + ethereumjs-testrpc@4.1.3 added 1 package and updated 7 packages in 76.132s liyuechun:~ yuechunli$ 

创建项目

/Users/liyuechun/Desktop/1012/Voting liyuechun:Voting yuechunli$ ls liyuechun:Voting yuechunli$ pwd /Users/liyuechun/Desktop/1012/Voting liyuechun:Voting yuechunli$ truffle unbox react-box Downloading... Unpacking... Setting up... Unbox successful. Sweet! Commands: Compile: truffle compile Migrate: truffle migrate Test contracts: truffle test Test dapp: npm test Run dev server: npm run start Build for production: npm run build liyuechun:Voting yuechunli$ 

项目结构

如何编写智能合约(Smart Contract)- 从零构建和部署去中心化投票App

  • contracts:编写智能合约的文件夹,所有的智能合约文件都放置在这里
  • migrations:部署合约配置的文件夹
  • src:基于React的Web端源码
  • test:智能合约测试用例文件夹

编写投票Dapp智能合约

contracts文件夹下创建Voting.sol文件,将下面的代码拷贝到文件中。

pragma solidity ^0.4.4; contract Voting { // liyuechun -> 10 // xietingfeng -> 5 // liudehua -> 20 mapping (bytes32 => uint8) public votesReceived; // 存储候选人名字的数组 bytes32[] public candidateList; // 构造函数 初始化候选人名单 function Voting(bytes32[] candidateNames) { candidateList = candidateNames; } // 查询某个候选人的总票数 function totalVotesFor(bytes32 candidate) constant returns (uint8) { require(validCandidate(candidate) == true); // 或者 // assert(validCandidate(candidate) == true); return votesReceived[candidate]; } // 为某个候选人投票 function voteForCandidate(bytes32 candidate) { assert(validCandidate(candidate) == true); votesReceived[candidate] += 1; } // 检索投票的姓名是不是候选人的名字 function validCandidate(bytes32 candidate) constant returns (bool) { for(uint i = 0; i < candidateList.length; i++) { if (candidateList[i] == candidate) { return true; } } return false; } } 

通过remix + metamask部署合约到Kovan Test Net

  • 在Google浏览器里面安装MetaMask插件

如何编写智能合约(Smart Contract)- 从零构建和部署去中心化投票App

如何编写智能合约(Smart Contract)- 从零构建和部署去中心化投票App

  • 确保MetaMask账号处于等于状态,并且有一定的以太币支付给矿工。
  • 确保EnvironmentInjected Web3,如果切换不过来,关掉浏览器重新启动
  • create函数中输入一个数组,数组里面的内容为候选人名单
  • 点击create按钮,会弹出MetaMask界面让你确认,确认提交,过一会儿,合约就部署成功
  • 可以测试给某个候选人投票,查询某个候选人的票数

拷贝合约地址

如何编写智能合约(Smart Contract)- 从零构建和部署去中心化投票App

0xd3f33a2e553b363b432d7f81f721a2a6202ecc67 

编译合约

liyuechun:Voting yuechunli$ truffle compile Compiling ./contracts/Migrations.sol... Compiling ./contracts/SimpleStorage.sol... Compiling ./contracts/Voting.sol... Writing artifacts to ./build/contracts liyuechun:Voting yuechunli$ 

编译完合约以后在build/contracts文件夹下面会有一个Voting.jsonabi文件。

查看Voting.json文件内容

{ "contract_name": "Voting", "abi": [ { "constant": true, "inputs": [ { "name": "candidate", "type": "bytes32" } ], "name": "totalVotesFor", "outputs": [ { "name": "", "type": "uint8" } ], "payable": false, "type": "function" }, { "constant": true, "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": "", "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" }, { "inputs": [ { "name": "candidateNames", "type": "bytes32[]" } ], "payable": false, "type": "constructor" } ], "unlinked_binary": "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", "networks": {}, "schema_version": "0.0.5", "updated_at": 1507806214330 } 

这个文件是编译后的abi文件,待会儿需要将这个文件的json导入到App.json中。

查看src/utils/getWeb3.js文件内容

import Web3 from 'web3' let getWeb3 = new Promise(function(resolve, reject) { // Wait for loading completion to avoid race conditions with web3 injection timing. window.addEventListener('load', function() { var results var web3 = window.web3 // Checking if Web3 has been injected by the browser (Mist/MetaMask) if (typeof web3 !== 'undefined') { // Use Mist/MetaMask's provider. web3 = new Web3(web3.currentProvider) results = { web3: web3 } console.log('Injected web3 detected.'); resolve(results) } else { // Fallback to localhost if no web3 injection. var provider = new Web3.providers.HttpProvider('http://localhost:8545') web3 = new Web3(provider) results = { web3: web3 } console.log('No web3 instance injected, using Local web3.'); resolve(results) } }) }) export default getWeb3 

这个文件主要是封装了一个getWeb3promiss供我们直接使用,可以从getWeb3直接获取到web3对象供App.js文件中使用。

修改app.js前端代码和合约进行互动

import React, { Component } from 'react' import VotingContract from '../build/contracts/Voting.json' import getWeb3 from './utils/getWeb3' import './css/oswald.css' import './css/open-sans.css' import './css/pure-min.css' import './App.css' const contractAddress = "0xd3f33a2e553b363b432d7f81f721a2a6202ecc67"; var votingContractInstance; var _modifyVotingCount = (candidates,i,votingCount) => { console.log("---------"); console.log(candidates); console.log(i); console.log(votingCount); let obj = candidates[i]; obj.votingCount = votingCount; return candidates; } class App extends Component { constructor(props) { super(props) this.state = { candidates: [ { "name": "Rama", "id": 100, "votingCount": 0 }, { "name": "Nick", "id": 101, "votingCount": 0 }, { "name": "Jose", "id": 102, "votingCount": 0 }, { "name": "liyuechun", "id": 103, "votingCount": 0 } ], candidatesVoteCount: ["0","0","0","0"], web3: null } } componentWillMount() { // Get network provider and web3 instance. // See utils/getWeb3 for more info. getWeb3 .then(results => { this.setState({ web3: results.web3 }) // Instantiate contract once web3 provided. this.instantiateContract() }) .catch(() => { console.log('Error finding web3.') }) } instantiateContract() { /* * SMART CONTRACT EXAMPLE * * Normally these functions would be called in the context of a * state management library, but for convenience I've placed them here. */ const contract = require('truffle-contract') const votingContract = contract(VotingContract) votingContract.setProvider(this.state.web3.currentProvider) // Declaring this for later so we can chain functions on SimpleStorage. // Get accounts. this.state.web3.eth.getAccounts((error, accounts) => { votingContract.at(contractAddress).then((instance) => { votingContractInstance = instance; for (let i = 0; i < this.state.candidates.length; i++) { let object = this.state.candidates[i]; console.log(accounts[0]); console.log(votingContractInstance); console.log(votingContractInstance.totalVotesFor(object.name)); votingContractInstance.totalVotesFor(object.name).then(result => { console.log(i); console.log(result.c[0]); this.setState({ candidates: _modifyVotingCount(this.state.candidates,i,result.c[0]) }); }); } }) }) } render() { return ( <div className="App"> <ul> { this.state.candidates.map((object) => { console.log(object); return ( <li key={object.id}>候选人:{object.name} 支持票数:{object.votingCount}</li> ) }) } </ul> <input style= placeholder="请输入候选人姓名..." ref="candidateInput" /> <button style= onClick={() => { console.log(this.refs.candidateInput); console.log(this.refs.candidateInput.value); let candidateName = this.refs.candidateInput.value; console.log(this.state.web3.eth.accounts[0]); votingContractInstance.voteForCandidate(candidateName).then((result => { console.log(result); console.log(candidateName); let number = 0; for(let i = 0; i < this.state.candidates.length; i++) { let object = this.state.candidates[i]; if (object.name === candidateName) { number = i; break; } } votingContractInstance.totalVotesFor(candidateName).then(result => { this.setState({ candidates: _modifyVotingCount(this.state.candidates,number,result.c[0]) }); }); })); }}>Voting</button> </div> ); } } export default App 

如何编写智能合约(Smart Contract)- 从零构建和部署去中心化投票App

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