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windows 10 64bit
youclavier -- 以太坊投票Dapp教程
準備接手一個IPFS+Ethereum的項目，先學習一下Ethereum，并嘗試完成一個Hello World。
nvm install 9.11.1
nvm use 9.11.1npm install ganache-cli
npm install web3@0.20.1
npm install solc@0.4.21 //此處原博客沒有版本，會安裝高于0.4的版本，會導致后續編譯smart contract編譯失敗 在安裝了ganache-cli與web3時，由于教程版本問題會出現報錯，但是不影響。
node_modules\.bin\ganache-cli
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;
}}
7. 啟動node交互控制臺，依次輸入以下命令Web3 = require('web3')
web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545"))
web3.eth.accounts輸入以上最后一條命令后會獲取Ganache創建的10個帳號，如下
> code = fs.readFileSync('Voting.sol').toString()
> solc = require('solc')
> compiledCode = solc.compile(code)全部完成會得到如下截圖的輸出，表示smart contract編譯成功
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此時會獲取address，記下來后續會用到
contractInstance = VotingContract.at(deployedContract.address)
- 下載web3.js文件，下載后放在工作根目錄下。
由cdn不知什么原因不可用，所以直接下載源文件，鏈接如下
web3.js 0.20.6- 在根目錄下創建index.html文件，并粘貼以下代碼，需要在截圖標出處，更換成第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 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>
11. 在瀏覽器打開index.html,輸入Candidate中的人名后，點擊Vote即可投票，投票后效果如下
每次點擊投票，也都會生成一個新的區塊，效果如下。
## 后記
以上步驟就完成了一個基于Ethereum的投票Dapp的完整搭建流程，整合個補全后步驟應該不會有坑的可以順利搭建完成。
就像“hello world”的字面意思一樣，0-1的過程是最艱難的，但是開了頭，剩下的1-n也就會順暢不少。
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