Nethereum:.NET应用和以太坊智能合约的桥梁

Nethereum基本上是目前唯一可用的.NET平台下的web3.js移植包。在这个教程中, 我们将首先编写并部署一个简单的智能合约,然后创建一个简单的.NET应用,并使用 Nethereum来访问以太坊上的智能合约。Nethereum是通过以太坊节点旳标准RPC接口 访问智能合约,因此使用Nethereum可以对接所有的以太坊节点实现,例如geth或parity。

如果你希望快速掌握Netherem的开发,可以访问汇智网的互动教程 C#以太坊开发详解, 技术问题可以直接咨询课程助教。

智能合约开发与部署

首先安装开发用以太坊节点软件Ganache:

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~$ npm install -g ganache-cli

然后安装以太坊开发框架Truffle:

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~$ npm install -g truffle

现在创建一个项目目录,进入该目录,并执行truffle init进行初始化:

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~$ mkdir demo && cd hubwiz
~/hubwiz$ truffle init

truffle会创建一些新的文件夹:contract、test、migration等。在contract 文件夹中,创建一个新的合约文件Vote.sol:

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~/hubwiz/contracts$ touch Vote.sol

按如下内容编辑Vote.sol,这个合约只是简单地跟踪两个候选人的得票数,它 使用交易发起账户作为投票人,并且每个账户只能投一票:

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pragma solidity ^0.4.16;

contract Vote {

uint public candidate1;
uint public candidate2;
mapping (address => bool) public voted;

function castVote(uint candidate) public {
require(!voted[msg.sender] && (candidate == 1 || candidate == 2));
if(candidate == 1){
candidate1++;
}else{
candidate2++;
}
voted[msg.sender] = true;
}
}

接下来在migration文件夹创建一个新的js文件2_vote.js,内容如下:

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var vote = artifacts.require("Vote");

module.exports = function(deployer) {
// deployment steps
deployer.deploy(vote);
};

然后打开项目文件夹下的truffle.js,用以下内容替换:

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module.exports = {
networks: {
ganache: {
host: "127.0.0.1",
port: 7545,
network_id: "*" // Match any network id
}
}
};

现在打开一个终端,启动ganache:

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~$ ganache-cli

然后打开另一个终端,用truffle部署合约:

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~/hubwiz$ truffle deploy --reset --network ganache

你会看到终端输出类似下面的合约地址,拷贝下来,后面还要用到:

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Vote: 0xe4e47451aad6c89a6d9e4ad104a7b77ffe1d3b36

.Net应用开发与智能合约访问

创建一个新的控制台项目,添加对如下开发包的依赖:

  • Nethereum.Web3
  • Nethereum.Contracts

然后按如下内容修改program.cs:

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using System;
using System.Numerics;
using System.Threading.Tasks;
using Nethereum.Contracts;
using Nethereum.Hex.HexTypes;
using Nethereum.Web3;

namespace console
{
class Program
{
static void Main(string[] args)
{
//The URL endpoint for the blockchain network.
string url = "HTTP://localhost:7545";

//The contract address:合约部署的地址
string address = "0x345cA3e014Aaf5dcA488057592ee47305D9B3e10";

//The ABI for the contract.
string ABI = @"[{'constant':true,'inputs':[],'name':'candidate1','outputs':[{'name':'','type':'uint256'}],'payable':false,'stateMutability':'view','type':'function'},{'constant':false,'inputs':[{'name':'candidate','type':'uint256'}],'name':'castVote','outputs':[],'payable':false,'stateMutability':'nonpayable','type':'function'},{'constant':true,'inputs':[],'name':'candidate2','outputs':[{'name':'','type':'uint256'}],'payable':false,'stateMutability':'view','type':'function'},{'constant':true,'inputs':[{'name':'','type':'address'}],'name':'voted','outputs':[{'name':'','type':'bool'}],'payable':false,'stateMutability':'view','type':'function'}]";

//Creates the connecto to the network and gets an instance of the contract.
Web3 web3 = new Web3(url);
Contract voteContract = web3.Eth.GetContract(ABI, address);

//Reads the vote count for Candidate 1 and Candidate 2
Task<BigInteger> candidate1Function = voteContract.GetFunction("candidate1").CallAsync<BigInteger>();
candidate1Function.Wait();
int candidate1 = (int)candidate1Function.Result;
Task<BigInteger> candidate2Function = voteContract.GetFunction("candidate2").CallAsync<BigInteger>();
candidate2Function.Wait();
int candidate2 = (int)candidate2Function.Result;
Console.WriteLine("Candidate 1 votes: {0}", candidate1);
Console.WriteLine("Candidate 2 votes: {0}", candidate2);

//Prompts for the account address.
Console.Write("Enter the address of your account: ");
string accountAddress = Console.ReadLine();

//Prompts for the users vote.
int vote = 0;
Console.Write("Press 1 to vote for candidate 1, Press 2 to vote for candidate 2: ");
Int32.TryParse(Convert.ToChar(Console.Read()).ToString(), out vote);
Console.WriteLine("You pressed {0}", vote);

//Executes the vote on the contract.
try{
HexBigInteger gas = new HexBigInteger(new BigInteger(400000));
HexBigInteger value = new HexBigInteger(new BigInteger(0));
Task<string> castVoteFunction = voteContract.GetFunction("castVote").SendTransactionAsync(accountAddress, gas, value, vote);
castVoteFunction.Wait();
Console.WriteLine("Vote Cast!");
}catch(Exception e){
Console.WriteLine("Error: {0}", e.Message);
}
}
}
}

别忘了用你自己部署的合约地址修改上面代码中的合约地址。现在运行应用,就可以投票了!

用Nethereum很容易就可以为.Net应用添加访问以太坊智能合约的能力,由于Nethereum基于.NET 平台,因此它可以用于.NET Core应用、.NET Standard应用、Xamarin以及各种windows应用中。


原文链接:Interfacing .NET and Ethereum Blockchain Smart Contracts with Nethereum

汇智网翻译,转载请标明出处。