Dapp简单的投票小例子
准备工作
相关命令
- mkdir simple_voting_dapp //创建文件夹
- cd simple_voting_dapp //进入文件夹
- npm init //初始化npm包管理文件，输入ls 可以看到创建的package.json文件
- npm intsall [email protected] //安装web3
- npm install [email protected] //安装solc
- npm install -g ganache-cli //安装ganache-cli 参考文档
- 输入ganache-cli 启动，出现如下界面，表示启动成功，列出10个账户以及各自的秘钥，每个账户都有100以太，这个类似dev私链的模式
Solidity合约
合约内容
- 构造函数，用来初始化一些候选者
- 用来投票的方法（对于票数加 1）
- 返回候选者获得的总的票数的方法
合约代码
pragma solidity ^0.4.22;
contract Voting{
mapping (bytes32 => uint8)public votesReceived;
bytes32[] public candidateList;
constructor(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 合约编译
编译前测试
- 查看安装的版本 npm list web3；npm list solc
- node 进入命令行
- var Web3 = require('web3')
- var web3 = new Web3(new Web3.providers.HttpProvider('Http://localhost:8545'))//这个需要和ganache-cli设置的一致，才可以连接上。
- 使用web3.isConnected()//查看是否连接上，此时需要将ganache-cli启动
- 使用命令web3.eth.accounts,获取目前的账户，需要注意每次启动ganache-cli都会产生全新的账号和秘钥
正式开始编译
- var solc = require('solc')
- 输入solc. 查看可以使用的命令
- var sourceCode = fs.readFileSync('Voting.sol').toString() //需要注意，必须给与文件读取权限
- 输入sourceCode 可以查看编码文件
- var compiledCode = solc.compile(sourceCode) //这个就是正式的编译过程
- 输入compiledCode可以查看字节码文件,编译结果如下图所示
- 这是一个js对象，最关键的是bytecode（字节码）和interface接口（ABI），这两个文件是部署合约最关键的文件
- 部署合约 var abi = JSON.parse(compiledCode.contracts[':Voting'].interface); 输入abi进行验证，是否取到正确的值，JSON.parse是为了Json格式化代码
- var byteCode = compiledCode.contracts[':Voting'].bytecode 取到字节码 其中:Voting是合约名称
- 创建合约对象 var VotingContract = web3.eth.contract(abi)
- var deployTxObj = {data:byteCode,from:web3.eth.accounts[0],gas:30000000} 定义一笔交易
- 定义合约实例 var contractInstance = VotingContract.new(["Alice","Bob","Cary"],deployTxObj);
- contractInstance = VotingContract.new(["Alice","Bob","Cary"],{data:byteCode,from:web3.eth.accounts[0],gas:5000000});
- 上面这一条命令是 定义合约实例 和 定义一笔交易的结合体，如果分开，有可能会报错
- 取到合约实例的地址 contractInstance.address 这就将合约部署在区块链上，这个区块链是本地起的ganache-cli模拟区块链
- contractInstance.vote("Alice",{from:web3.eth.accounts[0]}) 账号0给Alice投出一票
- contractINstance.totalVotesFor("Alice").toString() 查看Alice的总共的票数
- contractINstance.totalVotesFor.call("Alice").toString() 查看
- contractInstance.vote.sendTransaction("Alice",{from:web3.eth.accounts[0]})
页面交互
页面 index.html
Voting DApp
A Simple Voting Application
Candidate
Votes
Alice
Bob
Cary
Vote
注意
- 不再需要引入web3对象，因为页面里面就包含了web3对象，https://cdn.jsdelivr.net/gh/ethereum/web3.js/dist/web3.min.js，打开这个链接之后，在页面的最下面会显示，
index.js
var web3 = new Web3(new Web3.providers.HttpProvider("Http://localhost:8545"));
var abi = JSON.parse('[{"constant":true,"inputs":[{"name":"candidate","type":"bytes32"}],"name":"totalVotesFor","outputs":[{"name":"","type":"uint8"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"candidate","type":"bytes32"}],"name":"validCandidate","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"","type":"bytes32"}],"name":"votesReceived","outputs":[{"name":"","type":"uint8"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"","type":"uint256"}],"name":"candidateList","outputs":[{"name":"","type":"bytes32"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"candidate","type":"bytes32"}],"name":"voteForCandidate","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"inputs":[{"name":"candidateNames","type":"bytes32[]"}],"payable":false,"stateMutability":"nonpayable","type":"constructor"}]');
// var contractAddr = "0x3577f4d4902f4766753056468bd08ef68df6c623";
var VotingContract = new web3.eth.Contract(abi);
// var contractInstance =new web3.eth.Contract(abi,contractAddr);
// contractInstance = VotingContract.at(contractAddr);
var contractInstance = VotingContract.at('0x3577f4d4902f4766753056468bd08ef68df6c623');
var candidates = {
"Alice":"candidate-1",
"Bob":"candidate-2",
"Cary":"candidate-3"
};
function voteForCandidate(){
let candidateName = $("#candidate").val();
try{
contractInstance.voteForCandidate(candidateName),{from:web3.eth.accounts[0]},(err,res)=>{
if(err)
console.log("Error:",err);
else{
let div_id = candidates[candidateName];
let count = contractInstance.totalVotesFor(candidateName).toString();
$("#" + id).html(count);
}
}
}catch(err){
}
};
$(document).ready(function(){
candidateNames = Object.keys(candidates);
for(let i=0;i报错
无解
- at无法使用
- 如果使用 var contractInstance =new web3.eth.Contract(abi,contractAddr);避免了at，但是无法使用call回调函数，依然报错
部署服务
server.js
- 异步的方式启动，同步的会报错
var http = require('http');
var fs = require('fs');
var url = require('url');
http.createServer(function(req,res){
var pathName = url.parse(req.url).pathname;
console.log("Request for:"+pathName + "received.");
fs.readFile(pathName.substr(1),function(err,data){
if(err){
console.log(err);
res.writeHead(400,{'Content-Type':"text/html"});
}else{
res.writeHead(200,{'Content-Type':"text/html"});
res.write(data.toString());
}
res.end();
});
}).listen(8888);- 使用命令 node server.js启动服务器
- 浏览器输入 http://127.0.0.1:8888/index.html 查看
- 如果报错 没有favicon.ico 直接创建一个就好，这个是图标文件
