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;
}}
7. 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>
![更換address](https://user-images.githubusercontent.com/37465243/64078738-f976e400-cd10-11e9-82ef-20468a8e6ba5.png)
11. 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
![](https://user-images.githubusercontent.com/37465243/64078736-f8de4d80-cd10-11e9-9e1a-173c812f2264.png)
每次點擊投票,也都會生成一個新的區塊,效果如下。
![](https://user-images.githubusercontent.com/37465243/64078737-f8de4d80-cd10-11e9-874c-d3e8570432fb.png)
## 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。
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