Blockchain Smart Contracts with Solidity · 课时

ERC-721 非同质化代币（NFT）

探索用于独特数字资产的 ERC-721 标准，并学习如何铸造和管理 NFT。

ERC-721 非同质化代币（NFT） 是 CoddyKit 上的免费 Blockchain Smart Contracts with Solidity 课时。这是第 3 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Blockchain Smart Contracts with Solidity 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Blockchain Smart Contracts with Solidity 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Intro to Unique Digital Assets

Welcome to the world of Non-Fungible Tokens (NFTs)! Unlike regular money or cryptocurrencies, NFTs are unique digital items.

Think of them like rare collectibles or one-of-a-kind art pieces, but entirely digital. Each NFT has distinct properties and cannot be replaced by another.

The ERC-721 Standard

On Ethereum, NFTs are defined by a standard called ERC-721. This standard is a set of rules that smart contracts must follow to create, manage, and transfer unique tokens.

It ensures that all compliant NFTs work similarly across different platforms, making them interoperable.

Key Concepts: Token ID & Ownership

Every ERC-721 token has a unique Token ID (a large number). This ID distinguishes it from all other NFTs, even those from the same collection.

The standard also defines functions to track ownership:

ownerOf(uint256 tokenId): Returns the address that owns a specific NFT.
balanceOf(address owner): Returns the number of NFTs an address owns from that contract.

Building with OpenZeppelin

Creating an ERC-721 contract from scratch can be complex. Luckily, OpenZeppelin provides battle-tested, secure implementations.

We can simply import their contracts and build upon them. This saves time and reduces the risk of vulnerabilities.

Your First ERC-721 Contract

Here's a basic structure for an ERC-721 contract using OpenZeppelin. It defines a name and symbol for our NFT collection in the constructor.

We'll add a minting function next.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

contract SimpleNFT is ERC721 {
    constructor() ERC721("MySimpleNFT", "MSN") {
        // Constructor for ERC721 takes name and symbol
    }
}

Creating New NFTs: Minting

To bring new NFTs into existence, we use a process called minting. The _safeMint function (provided by OpenZeppelin's ERC721) creates a new token and assigns it to an owner.

Let's add a public mint function to our contract to create new NFTs.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

contract SimpleNFT is ERC721 {
    uint256 private _tokenIdCounter;

    constructor() ERC721("MySimpleNFT", "MSN") {
        _tokenIdCounter = 0;
    }

    function mint(address to) public returns (uint256) {
        uint256 newItemId = _tokenIdCounter;
        _tokenIdCounter++;
        _safeMint(to, newItemId); // Mints token and assigns to 'to' address
        return newItemId;
    }
}

NFT Metadata with Token URI

An NFT's value often comes from what it represents (an image, a song, a game item). This information, called metadata, isn't stored directly on the blockchain due to cost.

Instead, the ERC-721 standard includes a tokenURI(uint256 tokenId) function. This function returns a URL pointing to a JSON file that describes the NFT's metadata (e.g., name, description, image URL).

Transferring Ownership

Once an NFT is minted, it can be transferred between owners. The ERC-721 standard includes functions for this:

transferFrom(address from, address to, uint256 tokenId): Transfers ownership of tokenId from from to to.
safeTransferFrom(...): A safer version that checks if the recipient contract can receive NFTs.

These functions ensure only the current owner or an approved address can initiate a transfer.

Delegated Transfers: Approvals

Sometimes, you might want to allow another address (like a marketplace) to transfer your NFT on your behalf. This is done using approvals.

The approve(address to, uint256 tokenId) function lets you grant permission to another address to to manage a specific tokenId. This is crucial for decentralized exchanges and other dApps.

ERC-721 Knowledge Check

Let's test your understanding of ERC-721 NFTs. Select all statements that are true.

Recap: ERC-721 NFTs

You've explored the fascinating world of ERC-721 Non-Fungible Tokens!

NFTs are unique digital assets, unlike fungible cryptocurrencies.
The ERC-721 standard defines how these unique tokens are created and managed on Ethereum.
Key features include unique Token IDs, ownership tracking, minting, and linking to off-chain metadata via tokenURI.
OpenZeppelin contracts simplify ERC-721 development.

NFTs are a cornerstone of digital ownership and are used in art, gaming, and many other applications!

常见问题解答

「ERC-721 非同质化代币（NFT）」课时是免费的吗？

是的 — 「ERC-721 非同质化代币（NFT）」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Blockchain Smart Contracts with Solidity 课程的其余内容，请升级到 CoddyKit PRO。 Blockchain Smart Contracts with Solidity 课程共包含 4 节课。

「ERC-721 非同质化代币（NFT）」这节课中我会学到什么？

探索用于独特数字资产的 ERC-721 标准，并学习如何铸造和管理 NFT。你通过在浏览器中直接运行的动手代码来练习 Blockchain Smart Contracts with Solidity，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Blockchain Smart Contracts with Solidity 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Blockchain Smart Contracts with Solidity 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 3 节课，共 4 节。

「ERC-721 非同质化代币（NFT）」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Blockchain Smart Contracts with Solidity 课中编写并运行代码吗？

能。每节 Blockchain Smart Contracts with Solidity 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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