Non-Fungible Tokens (NFTs)

ERC-721, ERC-1155, metadata, marketplaces, and NFT development.

Overview

NFTs represent unique digital assets on the blockchain.

ERC-721 Standard

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";

contract MyNFT is ERC721, ERC721URIStorage {
    uint256 private _tokenIdCounter;
    
    constructor() ERC721("MyNFT", "MNFT") {}
    
    function mint(string memory uri) public {
        uint256 tokenId = _tokenIdCounter;
        _tokenIdCounter++;
        
        _safeMint(msg.sender, tokenId);
        _setTokenURI(tokenId, uri);
    }
}

ERC-1155 (Multi-Token)

import "@openzeppelin/contracts/token/ERC1155/ERC1155.sol";

contract GameItems is ERC1155 {
    uint256 public constant SWORD = 0;
    uint256 public constant SHIELD = 1;
    
    constructor() ERC1155("https://game.com/{id}.json") {
        _mint(msg.sender, SWORD, 100, "");
        _mint(msg.sender, SHIELD, 50, "");
    }
}

Metadata Structure

{
  "name": "Cool NFT #1",
  "description": "A unique digital collectible",
  "image": "ipfs://QmHash...",
  "attributes": [
    {"trait_type": "Background", "value": "Blue"},
    {"trait_type": "Rarity", "value": "Legendary"},
    {"trait_type": "Power", "display_type": "number", "value": 100}
  ]
}

Marketplace Contract

contract Marketplace {
    struct Listing {
        address seller;
        uint256 price;
        bool active;
    }
    
    mapping(uint256 => Listing) public listings;
    
    function list(uint256 tokenId, uint256 price) public {
        require(ownerOf(tokenId) == msg.sender);
        listings[tokenId] = Listing(msg.sender, price, true);
    }
    
    function buy(uint256 tokenId) public payable {
        Listing memory listing = listings[tokenId];
        require(listing.active);
        require(msg.value >= listing.price);
        
        // Transfer NFT and payment
        safeTransferFrom(listing.seller, msg.sender, tokenId);
        payable(listing.seller).transfer(msg.value);
    }
}

Practice

Mint and list an NFT on a marketplace.