使用truffle开发以太坊Dapp

  上一篇我们介绍了使用web3.js与以太坊智能合约交互,其中介绍了合约的编译、部署、执行等操作,但是很明显,如果要开发dapp,仅仅使用web3.js是不够的,开发繁琐,项目不够规范等。
今天我们就来介绍一种更快捷的方式:truffle,使用truffle能帮我们快速的搭建dapp项目,并规范项目结构,甚至truffle还提供了一些入门的dapp,帮助开发者快速上手。
本文主要介绍truffle提供的一个转账应用,如果需要学习更多的dapp,请移步 https://truffleframework.com/boxes

准备工作:
安装node,npm,这里就不介绍了,私有链仍然使用的是Ganache

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> npm install -g truffle

1、新建项目

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> mkdir demo && cd demo
> npm init

> truffle unbox webpack

# 如果需要搭建宠物商店,执行这条命令
> truffle unbox pet-shop

执行完之后,完整的项目结构如下:

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.
├── app
│   ├── index.html
│   ├── scripts
│   │   └── index.js
│   └── styles
│   └── app.css
├── box-img-lg.png
├── box-img-sm.png
├── build //智能合约编译后的内容
│   ├── app.js
│   ├── app.js.map
│   ├── contracts
│   │   ├── ConvertLib.json
│   │   ├── MetaCoin.json
│   │   └── Migrations.json
│   └── index.html
├── contracts //智能合约存放目录
│   ├── ConvertLib.sol
│   ├── MetaCoin.sol
│   └── Migrations.sol
├── migrations //智能合约部署信息
│   ├── 1_initial_migration.js
│   └── 2_deploy_contracts.js
├── package-lock.json
├── package.json
├── test //测试文件
│   ├── TestMetacoin.sol
│   └── metacoin.js
├── truffle.js //truffle配置
└── webpack.config.js

2、编译、部署
需要先启动Ganache,不然部署时连不上

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> truffle  migrate


# 编译成功后会显示如下内容
Writing artifacts to ./build/contracts

Using network 'development'.

Running migration: 1_initial_migration.js
Deploying Migrations...
... 0x1d307f4ba87bba7bfcbd06baf5fa8e2d2e64a8a69a18d8c56e277f36cc1d1677
Migrations: 0x42b27a0495c97b75e3f5ca6de5f45401320d7169
Saving successful migration to network...
... 0xf6d61e8a6840ac9438b6ddd64509f939438fe8eb7fa2f2283e2e9c52a1639857
Saving artifacts...
Running migration: 2_deploy_contracts.js
Deploying ConvertLib...
... 0xb8c26443eda840cbdc5e5a61b11678236b2fea14ffd1f8d9c2434cda9a1ba642
ConvertLib: 0x8d8f5fc48c5ab607b2eea17403d96c371895347f
Linking ConvertLib to MetaCoin
Deploying MetaCoin...
... 0xc9a2c12726cdd0a9160d832eed092d1a15b3a25a70dbe8b8cb9a079dedd5a345
MetaCoin: 0x84db03db9b32f49b054502e86fcfa9552052c10b
Saving successful migration to network...
... 0xc8f28755bd1094201014b13fb1f7773315e3b6f1f46a9e8e60b0567597888c52
Saving artifacts...

如果报这个错No network specified. Cannot determine current network.,找到truffle.js,把networks中的名称修改为development即可,因为默认连的就是development

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

如果报这个错误Attempting to run transaction which calls a contract function,删除build目录,重新执行truffle migrate命令
这个错误是因为编译后又修改了truffle.js中的development,地址不对导致的

3、启动项目

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> npm run dev

启动成功后,打开chrome浏览器http://localhost:8080/,会弹出一个错误,或者在You have META这个位置没显示余额,因为在app/avascripts/app.js文件中连的端口是9545,修改成7545,刷新页面就可以看到You have 10000 META
需要提醒的是:不需要装MetaMask,不需要装MetaMask,不需要装MetaMask!

如果你装了MetaMask,打开这个页面会显示You have 0 META,这是因为MetaMask提供了web3对象,所以根本不会连本机的http://localhost:8080/
具体代码可以查看app/avascripts/app.js,拉到文件最下方可以看到如下内容

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window.addEventListener('load', function () {
// Checking if Web3 has been injected by the browser (Mist/MetaMask)
if (typeof web3 !== 'undefined') {
console.warn(
'Using web3 detected from external source.' +
' If you find that your accounts don\'t appear or you have 0 MetaCoin,' +
' ensure you\'ve configured that source properly.' +
' If using MetaMask, see the following link.' +
' Feel free to delete this warning. :)' +
' http://truffleframework.com/tutorials/truffle-and-metamask'
)
// Use Mist/MetaMask's provider
window.web3 = new Web3(web3.currentProvider)
} else {
console.warn(
'No web3 detected. Falling back to http://127.0.0.1:9545.' +
' You should remove this fallback when you deploy live, as it\'s inherently insecure.' +
' Consider switching to Metamask for development.' +
' More info here: http://truffleframework.com/tutorials/truffle-and-metamask'
)
// fallback - use your fallback strategy (local node / hosted node + in-dapp id mgmt / fail)
window.web3 = new Web3(new Web3.providers.HttpProvider('http://127.0.0.1:9545'))
}

App.start()
})

所以如果你装了Metamask,就需要修改下文件,把web3对象是否存在的判断注释掉,并修改端口为7545,只保留window.web3 = new Web3(new Web3.providers.HttpProvider('http://127.0.0.1:7545')),具体修改如下

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window.addEventListener('load', function () {
// Checking if Web3 has been injected by the browser (Mist/MetaMask)
// if (typeof web3 !== 'undefined') {
// console.warn(
// 'Using web3 detected from external source.' +
// ' If you find that your accounts don\'t appear or you have 0 MetaCoin,' +
// ' ensure you\'ve configured that source properly.' +
// ' If using MetaMask, see the following link.' +
// ' Feel free to delete this warning. :)' +
// ' http://truffleframework.com/tutorials/truffle-and-metamask'
// )
// // Use Mist/MetaMask's provider
// window.web3 = new Web3(web3.currentProvider)
// } else {
// console.warn(
// 'No web3 detected. Falling back to http://127.0.0.1:9545.' +
// ' You should remove this fallback when you deploy live, as it\'s inherently insecure.' +
// ' Consider switching to Metamask for development.' +
// ' More info here: http://truffleframework.com/tutorials/truffle-and-metamask'
// )
// fallback - use your fallback strategy (local node / hosted node + in-dapp id mgmt / fail)
window.web3 = new Web3(new Web3.providers.HttpProvider('http://127.0.0.1:7545'))
// }

App.start()
})

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