ethereumsoliditysmartcontractsnft

How to update a NFT mint price by ethereum price in USD?

I am trying to build a smart contract that would give a fixed price in USD for each NFT to be minted by others, which they will need to pay in ETH. But I found a problem that the price of ETH is always changing, and each update of the NFT price in ETH would need some gas fee, which could cost a lot in long term for maintenance. Is there a way to periodically update ETH price inside the smart contract, or is manual updating the only way to do it?

Or I might have to remove the NFT price limit and completely rely on the frontend to handle the pricing part. But I think that's too risky.

Solution

  • You can use a Chainlink datafeed that returns the price of ETH in USD.

    There are no datafeeds in emulators (e.g. Ganache or the Remix IDE built-in network), so you can test this snippet on your local fork of the Ethereum mainnet.

    pragma solidity 0.8;

import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";

contract MyContract {
    AggregatorV3Interface priceFeed;
    // 18 decimals
    uint256 requiredPriceInUsd = 1000 * 1e18;

    constructor() {
        // https://etherscan.io/address/0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419#code
        // Chainlink ETH/USD Price Feed for Ethereum Mainnet
        priceFeed = AggregatorV3Interface(0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419);
    }

    // returns amount of wei
    function getRequiredPriceInWei() public view returns (uint256) {
        (,int answer,,,) = priceFeed.latestRoundData();

        // returned price is 8 decimals, convert to 18 decimals
        uint256 ethUsdPrice = uint256(answer) * 1e10;

        // 36 decimals / 18 decimals = 18 decimals
        return (requiredPriceInUsd * 1e18) / ethUsdPrice;
    }
}

    Output from my test: