如何实现onERC721Received函数

Question

我试图发送一个NFT到一个智能契约来托管，但是当我得到一个关于未使用的变量的错误时，很难实现重写函数onERC721Received --这就是我得到的错误吗？

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) {
| ^^^^^^^^^^^^^^^^^^

这是最明智的合同

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;
        }
    } 
    
    }

有人知道怎么解决这个问题吗？

Answer 1

你可以让警告像这样消失：

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

Answer 2

这只是一个警告--而不是错误--所以即使有警告，合同也会进行编译。

编译器告诉您您正在定义参数operator、tokenId、from和data，但您没有使用它们。但是，ERC721标准要求onERC721Received()函数接受所有这些参数，即使您可能不使用它们，因为函数选择器是从它们确定的。

所以你可以安全地忽略这个警告。