区块链 Hello World -- 基于以太坊的投票Dap

发布时间：2020-07-19 05:31:05 来源：网络阅读：219 作者：wx5b3c8b549a762 栏目：建站服务器

指路牌

以太坊
区块链
Dapp
以太坊hello world

环境

windows 10 64bit

参考博客

youclavier -- 以太坊投票Dapp教程

背景

准备接手一个IPFS+Ethereum的项目，先学习一下Ethereum，并尝试完成一个Hello World。

步骤

参考我另一片blog，安装nvm
安装node 9.11.1 并切换环境
```
nvm install 9.11.1
nvm use 9.11.1
```
创建一个新的工作目录，并在命令行索引到该路径

安装ganche-cli、web3、solc

npm install ganache-cli
npm install web3@0.20.1
npm install solc@0.4.21       //此处原博客没有版本，会安装高于0.4的版本，会导致后续编译smart contract编译失败

在安装了ganache-cli与web3时，由于教程版本问题会出现报错，但是不影响。

启动ganache-cli
```
node_modules\.bin\ganache-cli
```
使用Solidity创建Smart Contract,命名为：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. 启动node交互控制台，依次输入以下命令

Web3 = require('web3')
web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545"))
web3.eth.accounts
 输入以上最后一条命令后会获取Ganache创建的10个帐号，如下

区块链 Hello World -- 基于以太坊的投票Dap

> code = fs.readFileSync('Voting.sol').toString()
> solc = require('solc')
> compiledCode = solc.compile(code)

全部完成会得到如下截图的输出，表示smart contract编译成功
区块链 Hello World -- 基于以太坊的投票Dap
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

此时会获取address，记下来后续会用到

contractInstance = VotingContract.at(deployedContract.address)

下载web3.js文件，下载后放在工作根目录下。
由cdn不知什么原因不可用，所以直接下载源文件，链接如下
web3.js 0.20.6

在根目录下创建index.html文件，并粘贴以下代码，需要在截图标出处，更换成第8步自己部署的smart contract的address


&lt;!DOCTYPE html&gt;
&lt;html&gt;
&lt;head&gt;
&lt;title&gt;DApp&lt;/title&gt;
&lt;link href='https://fonts.googleapis.com/css?family=Open Sans:400,700' rel='stylesheet' type='text/css'&gt;
&lt;link href='https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css' rel='stylesheet' type='text/css'&gt;
&lt;/head&gt;
&lt;body class="container"&gt;
&lt;h2&gt;Voting Application&lt;/h2&gt;
&lt;div class="table-responsive"&gt;
&lt;table class="table table-bordered"&gt;
&lt;thead&gt;
&lt;tr&gt;
&lt;th&gt;Candidate&lt;/th&gt;
&lt;th&gt;Votes&lt;/th&gt;
&lt;/tr&gt;
&lt;/thead&gt;
&lt;tbody&gt;
&lt;tr&gt;
&lt;td&gt;James&lt;/td&gt;
&lt;td id="candidate-1"&gt;&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;
&lt;td&gt;Norah&lt;/td&gt;
&lt;td id="candidate-2"&gt;&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;
&lt;td&gt;Jones&lt;/td&gt;
&lt;td id="candidate-3"&gt;&lt;/td&gt;
&lt;/tr&gt;
&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;input type="text" id="candidate" /&gt;
&lt;a href="#" onclick="voteForCandidate()" class="btn btn-primary"&gt;Vote&lt;/a&gt;
&lt;/body&gt;

<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>


![更换address](https://user-images.githubusercontent.com/37465243/64078738-f976e400-cd10-11e9-82ef-20468a8e6ba5.png)

11. 在浏览器打开index.html,输入Candidate中的人名后，点击Vote即可投票，投票后效果如下
![](https://user-images.githubusercontent.com/37465243/64078736-f8de4d80-cd10-11e9-9e1a-173c812f2264.png)
每次点击投票，也都会生成一个新的区块，效果如下。
![](https://user-images.githubusercontent.com/37465243/64078737-f8de4d80-cd10-11e9-874c-d3e8570432fb.png)

## 后记
以上步骤就完成了一个基于Ethereum的投票Dapp的完整搭建流程，整合个补全后步骤应该不会有坑的可以顺利搭建完成。

就像“hello world”的字面意思一样，0-1的过程是最艰难的，但是开了头，剩下的1-n也就会顺畅不少。

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向AI问一下细节

区块链 Hello World -- 基于以太坊的投票Dap

指路牌

环境

参考博客

背景

步骤

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