Solidity: How to Set Price for NFT

EIP-721 is a specification on how Non-Fungible Token (NFT) should be implemented on Ethereum. You can use Solidity to build your own NFT that can be minted.

OpenZeppelin offers a simpler way to build your own NFT using their libraries.

Example contract

In the following source code, you're creating a new NFT, whose name is MyNFT and its unit is NFT.

This NFT does not come with Ownable OpenZeppelin libraly, meaning anyone can call mintNFT() RPC.

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

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

contract MyNFT is ERC721URIStorage {
    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;

    constructor() ERC721("MyNFT", "NFT") {}

    function mintNFT(address recipient, string memory tokenURI)
        public payable
        returns (uint256)
    {
        _tokenIds.increment();

        uint256 newItemId = _tokenIds.current();
        _mint(recipient, newItemId);
        _setTokenURI(newItemId, tokenURI);

        return newItemId;
    }
}

How to set price?

What if you'd like to set prices on this NFT? If your NFTs are on any NFT marketplaces, they may offer pricing features. But how to implement the price guard on Solidity?

This is fairly simple actually. Add a new require clause asserting that the passed msg.value is larger than the price.

    function mintNFT(address recipient, string memory tokenURI)
        public payable
        returns (uint256)
    {
+        require(msg.value >= 0.0001 ether, "Not enough ETH sent");