指路牌
- 以太坊
- 區塊鏈
- Dapp
- 以太坊hello world
環境
windows 10 64bit
參考博客
youclavier -- 以太坊投票Dapp教程
背景
準備接手一個IPFS+Ethereum的項目，先學習一下Ethereum，並嘗試完成一個Hello World。
步驟
- 參考我另一片blog， 安裝nvm
- 安裝node 9.11.1 並切換環境
nvm install 9.11.1
nvm use 9.11.1- 創建一個新的工作目錄，並在命令行索引到該路徑
- 安裝ganche-cli、web3、solc
npm install ganache-cli
npm install [email protected]
npm install [email protected] //此處原博客沒有版本，會安裝高於0.4的版本，會導致後續編譯smart contract編譯失敗 在安裝了ganache-cli與web3時，由於教程版本問題會出現報錯，但是不影響。
- 啓動ganache-cli
node_modules\.bin\ganache-cli
- 使用Solidity創建Smart Contract,命名爲：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;
}}- 啓動node交互控制檯，依次輸入以下命令
> Web3 = require('web3')
> web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545"))
> web3.eth.accounts輸入以上最後一條命令後會獲取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，記下來後續會用到
> contractInstance = VotingContract.at(deployedContract.address)-
下載web3.js文件，下載後放在工作根目錄下。
由cdn不知什麼原因不可用，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，並粘貼以下代碼，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 href='https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css' rel='stylesheet' type='text/css'>
</head>
<body class="container">
<h1>Voting Application</h1>
<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>
- 在瀏覽器打開index.html,輸入Candidate中的人名後，點擊Vote即可投票，投票後效果如下
每次點擊投票，也都會生成一個新的區塊，效果如下。
後記
以上步驟就完成了一個基於Ethereum的投票Dapp的完整搭建流程，整合個補全後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。