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6-5, web3 browser links to blockchain (react blockchain practice)

2024-07-12

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6-5，web3Browser link blockchain (react + blockchain practice)

6-5 Web3 browser links to blockchain (calling read and write contracts and linking with metamask)

Here is the interaction between the browser and the smart contract

Two libraries

Web3
Truffle contract //Truffle simply wraps the front-end contract in the link, which is more convenient to use

comeReact ProjectIn the root directory of (created in Chapter 1),
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Recreate a react project here
https://blog.csdn.net/u012118993/article/details/87288516
React creates a new project Use creat-react-app to quickly create a react project

（1）npm install -g create-react-app Install globally (install to the whole system)

（2）create-react-app reactproject Create a new react project and name it (note: the project name cannot be capitalized)

（3）cd reactproject Enter the folder through the command and prepare to run the project

（4）npm start Run the project

E:trufflewoniu-pet-shop

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Create in the truffle directory
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Install the following files in the react project
Install web3 (install to the folder below)

npm install web3 --save

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Then install truffle-contract

npm install truffle-contract --save

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Demo Completed

1. Linking Contract
2. Execute the internal functions of the contract
3. Add ant.design ui library support
4. Complete the project

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Note the new
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Contents of App.js
as follows

import React from 'react'
import Web3 from 'web3'
import TruffleContract from 'truffle-contract'
import AdoptionJson from './truffle/build/contracts/Adoption.json'	//引入前面智能合约编译好得到的json文件





class App extends React.Component{
	constructor(props){
		super(props)
		this.web3 = null
		this.Adoption = null
		this.init()

		this.state = {
			//name:'woniu'
		}
	}

	init(){
		//如果网页中的web3不是undefined
		if(typeof window.web3 != 'undefined'){
		}
	}

	render(){
		return <button></button>//hello,{this.state.name}
	}
}

export default App

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If the metamask plugin is installed in the browser

In the browser, global variables have values
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You can manually connect to metamask or automatically connect
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Start the script. Previously, web3 was undefined in the browser console because the webpage was empty.

Start in the petshop built by the react project

Npm start

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Open in browser
http://localhost:3000/

Video effects
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Video Installing a New Package
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There is an error in my own, because the init function is not saved

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The actual effect after success is as follows
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newly joined

init(){
		//如果网页中的web3不是undefined
		if(typeof window.web3 != 'undefined'){
			this.web3Provider = window.web3.currentProvider;	//metamask内置了web3的实例，实际可以手动链接
		}else{
			alert('请按照metamask')
		}
	}

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After changing the code and saving it, you can access the network again without shutting down and restarting npm start

Refresh now
Of course, there is no pop-up window at this time. After deleting the metamask wallet, there will be a pop-up window

At this time, use chrome browser without wallet to access
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A pop-up window appears, but some of the characters are garbled.

Add code

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All the codes are as follows

import React from 'react'
import Web3 from 'web3'
import TruffleContract from 'truffle-contract'
import AdoptionJson from './truffle/build/contracts/Adoption.json'	//引入前面智能合约编译好得到的json文件

//1.链接合约
//2.执行一下合约内部函数
//3.添加ant.design ui库支持
//4.完成项目
class App extends React.Component{
	constructor(props){
		super(props)
		this.web3 = null
		this.Adoption = null
		this.init()

		this.state = {
			//name:'woniu'
		}
	}

	init(){
		//如果网页中的web3不是undefined
		if(typeof window.web3 != 'undefined'){
			this.web3Provider = window.web3.currentProvider;	//metamask内置了web3的实例，实际可以手动链接
		}else{
			alert('please install metamask')
		}
		
		this.web3 = new Web3(this.web3Provider)		//将我们的this.web3Provider装载进来
		this.initAdoption()

	}

	initAdoption(){
		this.Adoption = TruffleContract(AdoptionJson)	//使用TruffleContract传入编译后的合约，然后创建实例，可以调用合约内部函数
		this.Adoption.setProvider(this.web3Provider)	//设置来源，链接合约
		return this.markAdopted()
	}
	
	//部署，这个是异步的，使用this.Adoption.deployed().then()也可以，这里用
	//this.markAdopted(){
		//部署链接一下
	//	const adoptionInstance = this.Adoption.deployed().then()	

	//}

	async markAdopted(){
		//部署链接一下
		//await同步方式获取异步数据
		const adoptionInstance = await this.Adoption.deployed()	//部署，这个是异步的，使用this.Adoption.deployed().then()也可以，这里用
		//调用合约内部函数getAdopters
		const adopters = await adoptionInstance.getAdopters.call()
		console.log(adopters)
	}

	render(){
		return <button></button>//hello,{this.state.name}
	}
}

export default App

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The refresh interface is as follows
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Get the address of the contract
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Use the variables above to get the local address and the default account address of metamask
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https://blog.csdn.net/weixin_41937552/article/details/106990561?utm_medium=distribute.pc_relevant.none-task-blog-baidujs_title-1&spm=1001.2101.3001.4242

The reason why the metamask address cannot be obtained here is as above
https://blog.csdn.net/weixin_39421014/article/details/103323245

You can turn off the privacy permission of metamask first
https://www.freesion.com/article/8518937500/
Privacy mode settings and compatible JS code
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https://blog.csdn.net/JackieDYH/article/details/115380677?utm_medium=distribute.pc_relevant.none-task-blog-baidujs_title-0&spm=1001.2101.3001.4242
Get account information

After the code is modified, modify it in the initialization function part.

You can use metamask to link to the website and print out the current metamask address
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Next, change the code for the click event
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Clicking on adoption here will pop up a box for payment, because you need to call the write function and write it to the chain. The adoption here does not require money transfer but requires the parent fee.

The local function that needs to be written to the blockchain is successfully called (as shown below when the button is clicked)
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All the codes that finally ran successfully are as follows:

import React from 'react'
import Web3 from 'web3'
import TruffleContract from 'truffle-contract'
import AdoptionJson from './truffle/build/contracts/Adoption.json'	//引入前面智能合约编译好得到的json文件

//1.链接合约
//2.执行一下合约内部函数
//3.添加ant.design ui库支持
//4.完成项目
class App extends React.Component{
	constructor(props){
		super(props)
		this.web3 = null
		this.Adoption = null
		this.init()

		this.state = {
			//name:'woniu'
		}
	}

	async init(){
		//如果网页中的web3不是undefined
		//if(typeof window.web3 != 'undefined'){
		//	this.web3Provider = window.web3.currentProvider;	//metamask内置了web3的实例，实际可以手动链接
		//}else{
		//	alert('please install metamask')
		//}
		
		//this.web3 = new Web3(this.web3Provider)		//将我们的this.web3Provider装载进来
		//this.initAdoption()
		
		/* 新版的方式 */
	  //var web3Provider;
	  if (window.ethereum) {
		this.web3Provider = window.ethereum;
		try {
		  // 请求用户授权
		  await window.ethereum.enable();
		} catch (error) {
		  // 用户不授权时
		  console.error("User denied account access")
		}
	  } else if (window.web3) {   // 老版 MetaMask Legacy dapp browsers...
		this.web3Provider = window.web3.currentProvider;
	  } else {
		this.web3Provider = new Web3.providers.HttpProvider('http://localhost:7545');
	  }
	  this.web3 = new Web3(this.web3Provider);//web3js就是你需要的web3实例
	  

	  this.web3.eth.getAccounts(function (error, result) {
		if (!error)
		  console.log(result)//授权成功后result能正常获取到账号了
		  //this.account = result
	  });
	  //this.account =result
	  //this.account =account
	  this.initAdoption()
	}

	initAdoption(){
		this.Adoption = TruffleContract(AdoptionJson)	//使用TruffleContract传入编译后的合约，然后创建实例，可以调用合约内部函数
		this.Adoption.setProvider(this.web3Provider)	//设置来源，链接合约
		return this.markAdopted()
	}
	
	//部署，这个是异步的，使用this.Adoption.deployed().then()也可以，这里用
	//this.markAdopted(){
		//部署链接一下
	//	const adoptionInstance = this.Adoption.deployed().then()	

	//}

	async markAdopted(){
		//部署链接一下
		//await同步方式获取异步数据
		const adoptionInstance = await this.Adoption.deployed()	//部署，这个是异步的，使用this.Adoption.deployed().then()也可以，这里用
		//调用合约内部函数getAdopters
		const adopters = await adoptionInstance.getAdopters.call()
		console.log(adopters)
	}
	
	async adopt(petId){
		//const account = window.web3.eth.defaultAccount		//获取metamask中默认的账户
		// 授权获取账户
	    const accounts = await window.ethereum.request({ method: 'eth_requestAccounts' });
        const myAccount = accounts[0];	//获取当前metamask的地址

		const adoptionInstance = await this.Adoption.deployed()		//再次进行部署
		await adoptionInstance.adopt(petId,{from:myAccount})	//调用adopt只传递唯一一个参数，以及来源之前获取的地址，进行写入函数
		this.markAdopted()
	}

	render(){
		//onclick点击事件，调用领养函数
		return <button onClick={()=>this.adopt(2)}>领养第二个</button>//hello,{this.state.name}
	}
}

export default App

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All functions have been successfully executed, read and write functions

This code has some defects. If the transaction fails, an error will be reported, and the page will also report an error.
Click Reject or exit directly
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The next step is to beautify the UI

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