如何編寫智能合約（Smart Contract）- 從零構建和部署去中心化投票App，decentralization Voting Dapp

孔壹學院：國內區塊鏈職業教育領先品牌

作者：黎躍春，區塊鏈、高可用架構工程師
微信：liyc1215 QQ羣：348924182 博客：http://liyuechun.org

課程目標

瞭解區塊鏈智能合約
學會搭建智能合約開發環境
學會如何編譯智能合約
學會如何將智能合約部署到區塊鏈
學會如何通過WebApp和智能合約盡心互動
掌握DApp（去中心化App）的整個開發部署流程
掌握去中心化在實戰產品中應用的重大意義

項目效果圖

編輯器選擇

理論上講任何編輯器都可以編寫Solidity合約代碼，比如：WebStorm，VSCode，Sublime，等等。我選擇的是Atom，沒有任何理由，因爲Atom輕量並且界面漂亮。

移步https://atom.io/地址，下載安裝Atom。
autocomplete-solidity代碼自動補齊

linter-solium、linter-solidity代碼錯誤檢查
language-ethereum支持Solidity代碼高亮以及Solidity代碼片段

安裝所需工具

首先開發機上必須裝好Node.js，再使用以下命令安裝所需的工具：

$ 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$

創建項目

/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$

項目結構

contracts：編寫智能合約的文件夾，所有的智能合約文件都放置在這裏
migrations：部署合約配置的文件夾
src：基於React的Web端源碼
test：智能合約測試用例文件夾

編寫投票Dapp智能合約

在contracts文件夾下創建Voting.sol文件，將下面的代碼拷貝到文件中。

pragma solidity ^0.4.4;

contract Voting {

  // liyuechun -> 10
  // xietingfeng -> 5
  // liudehua -> 20
  mapping (bytes32 => uint8) public votesReceived;


  // 存儲候選人名字的數組
  bytes32[] public candidateList;


  // 構造函數 初始化候選人名單
  function Voting(bytes32[] candidateNames) {

    candidateList = candidateNames;
  }

  // 查詢某個候選人的總票數
  function totalVotesFor(bytes32 candidate)  constant returns (uint8) {
    require(validCandidate(candidate) == true);
    // 或者
    // assert(validCandidate(candidate) == true);
    return votesReceived[candidate];
  }

  // 爲某個候選人投票
  function voteForCandidate(bytes32 candidate) {
    assert(validCandidate(candidate) == true);
    votesReceived[candidate] += 1;
  }

  // 檢索投票的姓名是不是候選人的名字
  function validCandidate(bytes32 candidate) constant returns (bool) {
    for(uint i = 0; i < candidateList.length; i++) {
      if (candidateList[i] == candidate) {
        return true;
      }
    }
    return false;
  }
}

通過remix + metamask部署合約到Kovan Test Net

在Google瀏覽器裏面安裝MetaMask插件

打開https://remix.ethereum.org將合約代碼拷貝到裏面

確保MetaMask賬號處於等於狀態，並且有一定的以太幣支付給礦工。
確保Environment是Injected Web3，如果切換不過來，關掉瀏覽器重新啓動
在create函數中輸入一個數組，數組裏面的內容爲候選人名單
點擊create按鈕，會彈出MetaMask界面讓你確認，確認提交，過一會兒，合約就部署成功
可以測試給某個候選人投票，查詢某個候選人的票數

拷貝合約地址

0xd3f33a2e553b363b432d7f81f721a2a6202ecc67

編譯合約

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$

編譯完合約以後在build/contracts文件夾下面會有一個Voting.json的abi文件。

查看Voting.json文件內容

{
  "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
}

這個文件是編譯後的abi文件，待會兒需要將這個文件的json導入到App.json中。

查看src/utils/getWeb3.js文件內容

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

這個文件主要是封裝了一個getWeb3的promiss供我們直接使用，可以從getWeb3直接獲取到web3對象供App.js文件中使用。

修改app.js前端代碼和合約進行互動

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}>候選人：{object.name}          支持票數：{object.votingCount}</li>
            )
         })
        }
      </ul>

      <input
            style={{width: 200,height: 30,borderWidth: 2,marginLeft: 40}}
            placeholder="請輸入候選人姓名..."
            ref="candidateInput"
      />

      <button style={{height: 30,borderWidth: 2,marginLeft: 20}} 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

打賞地址

**比特幣：**1FcbBw62FHBJKTiLGNoguSwkBdVnJQ9NUn
**以太坊：**0xF055775eBD516e7419ae486C1d50C682d4170645

技術交流

區塊鏈技術交流QQ羣：348924182

如何編寫智能合約（Smart Contract）- 從零構建和部署去中心化投票App，decentralization Voting Dapp

課程目標

項目效果圖

編輯器選擇

安裝所需工具

創建項目

項目結構

編寫投票Dapp智能合約

通過remix + metamask部署合約到Kovan Test Net

拷貝合約地址

編譯合約

查看Voting.json文件內容

查看src/utils/getWeb3.js文件內容

修改app.js前端代碼和合約進行互動

打賞地址

技術交流

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