检查所有者是 msg.sender，但仍然给出 ERC721：transfer caller is not owner nor approved

Question

I can't seem to figure out what is wrong, even looking at other questions posted. The token should be holding the nft

In the NFT contract,

function NFTMe(string memory tokenUR) public returns (uint256) {
        uint256 newTokenId = _tokenIds.current();
        _mint(msg.sender, newTokenId);
        _setTokenURI(newTokenId, tokenUR);
        // setApprovalForAll(msg.sender, true); <-- this will give me reverted with reason string 'ERC721: approve to caller'
        _tokenIds.increment();
        return newId ;
    }

I have another function to see who is the owner:

function getOwner(uint256 tokenId) public view returns(address) {
        address owner = ERC721.ownerOf(tokenId);
        return owner;
    }

When I deploy, it says currentOwner is the owner who minted it.

In the token,

constructor( string memory _name, string memory _symbol, address nftAddr) ERC20(_name, _symbol) {
nft = IERC721(nftAddr);
}
function transfer() public {
    // 'ERC721: transfer caller is not owner nor approved'
    nft.transferFrom(msg.sender, address(this), nftId); 
 }

Answer 1

// 'ERC721: transfer caller is not owner nor approved'
nft.transferFrom(msg.sender, address(this), nftId); 

In this case, the "transfer caller" is your token contract. Which is not the token owner, not approved by the user (the token owner) to transfer the token.

The easiest solution is to make the token contract automatically approved by the user from within the NFTMe() function in the NFT contract:

_approve(tokenContractAddress, newTokenId);