8BTCCI: 14248.33 +3.26% 8BTCVI: 6466.67 +8.74% 24H成交额: ¥4550.26亿 +20.88% 总市值: ¥19487.04亿 +2.30%
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

黎跃春(愿码ChainDesk.CN) 发布在 技术指南 113302

 

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

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
p2
  • 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
p3

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

p4
  • 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
p5 p6
  • 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

p7
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

评论(9)
登录 账号发表你的看法,还没有账号?立即免费 注册
  • 巴比特资讯 2017-10-30
    【如何编写智能合约(Smart Contract)- 从零构建和部署去中心化投票App】 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 …… 动图演示—》 http://t.cn/RW3EH3d ​
    • sloong: 2017-12-13
      请教博主,按照步骤过来,一切都ok,在投票时,出现异常。后台跟踪是在打印账户地址后,报地址错误
  • 大杯可乐hey 2017-10-30
    妈耶,好想试试[跪了]
  • sloong 2017-12-13
    为什么不能评论
  • sloong 2017-12-13
    请教,按照文章一步步过来,最后卡在 投票的环节,说是地址异常
  • sloong 2017-12-13
    博主,还是换个技术论坛发表吧,这评论做得跟屎一样
  • 冬至130 2017-10-30
    如何编写智能合约(Smart Contract)- 从零构建和部署去中心化投票App_巴比特_服务于区块链创新者 课程目标了解区块链智能合约学会搭建智能合约开发环境学会如何编译智能合约学会如何将智能合约部署到区块链学会如何... http://t.cn/RW3EH3d ​
  • 淘西西 2018-03-28
    mark,学习
  • 卡士大夫的 2018-06-11
    谢谢巴比特的分享。推荐个以太坊智能合约教程:http://t.cn/RmhKhej