如何将令牌发送到 ERC721 合约？

Question

I have a ERC721 contract, and my mint method requires 1 ether. My contract is here:

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

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

contract Example is ERC721 {

    uint256 private _tokenId = 0;

    function mint(uint256 tokenURI, uint256 id) public payable returns(uint256){
        require(msg.value == 1 ether);
        require(id > 0);
        
        _tokenId += 1;
        _mint(msg.sender, _tokenId);
        _setTokenURI(_tokenId, tokenURI);
        return _tokenId;
    }
}

My question is how can I know where that value is stored? On the explorer, I can see there's 1 ether on the contract address, how can I get the token out? Using balanceOf from ERC721 can only get the number of tokens that an address have. I want to see the values on this contract address.

Answer 1

Your question is not 100% clear but it looks like you are not able to get tokens data because your contract does not store any token.

You are missing many basic things in your smart contract. For example where are the tokens stored? I cannot see any array for that. What is the data associated with a token? I cannot see any struct defined.

Once you define how the tokens are stored then you can retrieve their data.

Please note the example below is just to show you a basic implementation and many things have to be defined. If you just copy and paste it then it won't work.

YourTokenStruct[] public yourTokens;

struct YourTokenStruct {
    string name;
    uint256 id;
}

function mint(string memory name, uint256 id) public payable returns(uint256){
    require(msg.value == 1 ether);
    require(id > 0);
    
    uint _tokenId = yourTokens.push(YourTokenStruct(name, id)) - 1;

    _mint(msg.sender, _tokenId);

    return _tokenId;
}

As you can see the array yourTokens stores all tokens created, and the struct YourTokenStruct defines the data structure of a token.

I suggest you to follow the tutorial https://cryptozombies.io/ it explains all the basics on how to code ERC721 token standard.

---

EDIT: The ether is stored on the smart contract address (the address where the contract has been deployed). Below an example of a function that transfers the ether from the smart contract to the caller of the function (of course define the modifier ifOwner yourself):

function withdraw() payable external ifOwner {
    msg.sender.transfer(address(this).balance);
}