3. "Create your own NFT collections and publish a Web3 application to show them" cast NFT locally

Write our entry contract .

First, let's do a little cleaning up .

We want to remove some automatically generated but less needed code . We have to write it ourselves .

First look at the directory structure ：

Delete first test Under folder sample-test.js file .

Then delete scripts In the catalog sample-script.js file ,

Finally delete contracts In the catalog Greeter.sol.

Be careful , Just delete the file , Do not delete the folder where these files are located ！

Now? , stay VSCode Open project in , Let's start writing NFT contract . If you have never written a smart contract , Please don't worry . Follow our tutorial . If you still don't understand, you can Google or ask questions on the message board .

stay contracts Under the table of contents , Create a file named ：MyEpicNFT.sol. In the use of Hardhat The file structure is very important , So be careful here ！

Be careful ： I suggest you download VSCode Of Solidity Expand , It provides good syntax highlighting .

Here we start with a very basic contract , From shallow to deep .

// SPDX-License-Identifier: UNLICENSED

pragma solidity ^0.8.1;

import "hardhat/console.sol";

contract MyEpicNFT {
    constructor() {
        console.log("This is my NFT contract. Whoa!");
    }
}

Be careful ： Sometimes VSCode Itself will throw an untrue error , for example , It may be in hardhat Import the underline and say it doesn't exist . These may be because of your overall situation Solidity The compiler is not set locally . If you don't know how to solve this problem , These can be ignored for the time being . In addition, I advise you not to use VSCode Terminal , Use your own separate terminal ！ If the compiler is not set , Sometimes VSCode The terminal will have problems .

Let's explain line by line here ：

// SPDX-License-Identifier: UNLICENSED

Just a comment . It is called “SPDX License identifier ”, You can Here, Read more about .

pragma solidity ^0.8.1;

This is what we want the contract to use Solidity The version of the compiler . It means ：“ When running this program , I just want to use version 0.8.1 Or higher, but not higher than 0.9.0 Of Solidity compiler . Be careful , Please make sure that hardhat.config.js The compiler is set accordingly （ for example 0.8.1）.

import "hardhat/console.sol";

Hardhat It allows us to execute some console logs in the contract . Debugging smart contracts is actually challenging , This is a Hardhat One of the relatively easy ways for us .

contract MyEpicNFT {
    constructor() {
        console.log("This is my NFT contract. Whoa!");
    }
}

Smart contracts are a bit like those in other languages class . If we initialize this contract for the first time , That constructor will run and print out this line . You can, too 、 You can modify the printed line , Change to something else you want to print .

How do we run it ？

Now we have a smart contract ！ however , We don't know whether it works . We actually need ：

1. Compile it .
2. Deploy it to our local blockchain .
3. Once it is deployed there ,console.log It will run .

We will write a custom script to handle this for us 3 A step .

Get into scripts And create a directory called run.js The file of .

This is a run.js What's in it ：

const main = async () => {
    
  const nftContractFactory = await hre.ethers.getContractFactory('MyEpicNFT');
  const nftContract = await nftContractFactory.deploy();
  await nftContract.deployed();
  console.log("Contract deployed to:", nftContract.address);
};

const runMain = async () => {
    
  try {
    
    await main();
    process.exit(0);
  } catch (error) {
    
    console.log(error);
    process.exit(1);
  }
};

runMain();

How it works ？

Be careful ：VSCode Ethereum may be automatically imported . We don't need to import ether .

Let's explain the above code line by line .

const nftContractFactory = await hre.ethers.getContractFactory("MyEpicNFT");

This will actually compile our contract and generate the necessary file directories in the directory we need to use the contract artifacts . Check it after running .

const nftContract = await nftContractFactory.deploy();

What's going on here is ,Hardhat Will create a local Ethereum network for us , But just for this contract . then , After the script is completed , It will destroy the local network . therefore , Every time you run a contract , It will be a new blockchain . What's the point ？ It's a bit like refreshing your local server every time , So always start from scratch , This makes it easy to debug errors .

await nftContract.deployed();

We will wait until our contracts are officially mined and deployed to our local blockchain ！hardhat In fact, a fake is created on your machine “ The miners ”, Try to imitate the actual blockchain .

Our constructor constructor Run at actual full deployment ！

console.log("Contract deployed to:", nftContract.address);

Last , Once the deployment is complete , Will give us the address of the deployment contract nftContract.address . This address is the way we really find the contract on the blockchain . But now on our local blockchain , Only us .

however , There are actually millions of contracts on the blockchain . therefore , This address allows us to easily access the contracts we are interested in ！ In the next few classes , When we deploy the contract to the actual blockchain , This can come in handy .

function .

Before running this function , Please ensure that the hardhat.config.js Medium solidity: “0.8.4” Change to solidity: “0.8.1”.

Let's run it ！ Open your terminal and run it ：

npx hardhat run scripts/run.js

You can see what runs in the contract console.log , The printed contract address ！！！ This is what I got ：

Hardhat & HRE

In these code blocks , You will notice that we often use hre.ethers, but hre Never imported anywhere ？ So why can it be used ？

Go straight to see it Hardhat file , You will notice this ：

Hardhat Runtime Environment, Or abbreviation HRE, Is a containing Hardhat Running tasks 、 The object of all functions exposed when testing or scripting . actually ,Hardhat Namely HRE.

So what does that mean ？ ok , Each time you run one with npx hardhat At the beginning of the terminal command , You use the code specified hardhat.config.js State build this hre object ！ This means that you will never have to actually import a file of some kind , for example ：

const hardhat = require("hardhat")