How to implement onERC721Received function

Question

I am trying to send an NFT to a smart contract to hold in escrow but am having a tough time implementing the overriding function onERC721Received as I get an error about unused variables - this is the error im getting ?

Warning: Unused function parameter. Remove or comment out the variable name to silence this warning.
--> contracts/NftEscrow.sol:11:79:
|
11 | function onERC721Received(address _operator, address _from, uint256 _tokenId, bytes memory _data) public override returns(bytes4) {
| ^^^^^^^^^^^^^^^^^^

This is the smart contract

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol";

    
    contract nftescrow is IERC721Receiver {
        
        enum ProjectState {newEscrow, nftDeposited, cancelNFT, ethDeposited, canceledBeforeDelivery, deliveryInitiated, delivered}
        
        address payable public sellerAddress;
        address payable public buyerAddress;
        address public nftAddress;
        uint256 tokenID;
        bool buyerCancel = false;
        bool sellerCancel = false;
        ProjectState public projectState;
    
        constructor()
        {
            sellerAddress = payable(msg.sender);
            projectState = ProjectState.newEscrow;
        }
        
        function onERC721Received( address operator, address from, uint256 tokenId, bytes calldata data ) public override returns (bytes4) {
            return this.onERC721Received.selector;
        }
        
        function depositNFT(address _NFTAddress, uint256 _TokenID)
            public
            inProjectState(ProjectState.newEscrow)
            onlySeller
        {
            nftAddress = _NFTAddress;
            tokenID = _TokenID;
            ERC721(nftAddress).safeTransferFrom(msg.sender, address(this), tokenID);
            projectState = ProjectState.nftDeposited;
        }
    } 
    
    }

Does anyone have any idea how to fix this?

Answer 1

You can make the warning disappear like this:

    function onERC721Received(address, address, uint256, bytes calldata) external pure returns (bytes4) {
        return IERC721Receiver.onERC721Received.selector;
    }