ERC721 how works setApproveForAll

Question

i do auction of nft contract. I have a complex structure:

• Contraact Users has array of User contracts, instance of NFT contract and instance of Auctions contract

• NFt contract has createNFT and transferNFT methods.

• Auctions contract has array of Auction contracts and methods to create new auction (auctions.push(new Auction(some, params)))

• Auction contract receives in constructor some params and tokenId of nft. And there are methods: placeBid and finalizeAuction(transfer eth to owner and transfer nft to bidder) in Auction contract

• And finally User contract has methods: collectNFT - by nftInstance of Users call createNFT and save tokenId. Next createAuction method by auctionInstance in Users call createAuction. Also, user can placeBid and finalizeAuction.

So, we have 2 users. The first creates new NFT, provide tokenId in createAuction. The second places a bid. Then the first finalize auction. BUT I GET ERROR - Revert ERC721: transfer caller is not owner nor approved. I know what there is setApproveForAll method, but where to call it??

I don't even know why the owner is not approved!

I tried in NFT contract call setApproveForAll(userAddress), next in User contract setApproveForAll(address(auctionsInstance)), in Auctions do that for Auction contract. But any way it is ERROR.

How is setApproveForAll works?? How to fix that? Please help me;)

Answer 1

The code for setApprovalForAll is :

function setApprovalForAll(address operator, bool approved) public virtual override {
    _setApprovalForAll(_msgSender(), operator, approved);
}

See here

So to approve all the tokens the user who wants to approve their tokens must call the function with the parameters: user address they want to approve, and the boolean true. To revoke the permissions you must call the same function with the boolean false.

Note: the approved user is not the owner, they are simply an approvee, you can use isApprovedForAll to check if you are approved.