How to send an NFT to another wallet and sing the transaction in Metamask?

Question

I'm a beginner and trying to learn web3 and want to implement a transfer-button for NFTs (same as you have on Opensea, where you can transfer your NFT to another address).

I have started of by having a React-website where you can connect your Metamask wallet and thereafter I scan the connected wallet for all NFTs using the alchemy-sdk to get contract, ids and so on.

Next step is to do the actual transaction and here I'm a bit lost.

I see that the same library has a method for sending a transaction with

alchemy.transact.sendTransaction()

But here I first need a signed transaction and here I'm a bit stuck.

For a normal ETH-transfer it seems a transaction looks something like this (found when I searched)

let transaction = {
    to: "TO-ACCOUNT",
    value: Utils.parseEther("0.001"),
    gasLimit: "21000",
    maxPriorityFeePerGas: Utils.parseUnits("5", "gwei"),
    maxFeePerGas: Utils.parseUnits("20", "gwei"),
    nonce: nonce,
    type: 2,
    chainId: 5,
  };

But how does a transaction looks like when sending an NFT, and how do I sign it in Metamask before using the sendTransaction method?

Or is there another way I should approach this problem :)

Answer 1

I finally figured it out by myself, so here is the answer if anyone else is wondering about how to do it.

To transfer an NFT you need to create a eth_sendTransaction request

         const transactionParameters = {
             to: nftContractAddress,
             from:  ownerAddress,
             value: '0',
             data: encodedData
         };

         const txHash = window.ethereum.request({
             method: 'eth_sendTransaction',
             params: [transactionParameters],
         });

Where the encodedData is an encoded transaction containing the toAddress, fromAddress and tokenId.

Since NFTS follow the ERC729-standard they all have a method called safeTransferFrom.

You can create the encoded data doing the following using the ethers package that will use for all NFTs following the standard.

  let iface = new ethers.utils.Interface(erc729Abi)
  return iface.encodeFunctionData("safeTransferFrom", [
    ethers.utils.getAddress(ownerAddress), ethers.utils.getAddress(toAddress), tokenId
  ])
```

Here **erc729Abi** is an ABI containing just the safeTransferFrom, but I suppose passing the whole contract also will work.

stripped erc729Abi I use above
```
[
  {
    "inputs": [
      {
        "internalType": "address",
        "name": "from",
        "type": "address"
      },
      {
        "internalType": "address",
        "name": "to",
        "type": "address"
      },
      {
        "internalType": "uint256",
        "name": "tokenId",
        "type": "uint256"
      }
    ],
    "name": "safeTransferFrom",
    "outputs": [],
    "stateMutability": "nonpayable",
    "type": "function"
  }
]

```