如何从另一个智能合约 function 调用智能合约 function？

Question

Some background first. I have two smart contracts:

• ERC20 for fungible tokens where I minted my own token/crypto currency;
• ERC1155 for non-fungible tokens (NFTs);
• The user will buy the NFT minted in the ERC1155 with the token I minted in the ERC20 smart contract.

The user calls the function buyNFT() in the ERC1155 that call the function transfer() inside the ERC20 smart contract. My problem relies in making the "bridge" between these two contracts. I've tried using the low-level function delegatecall() but with no success since it always returns a tuple whose first value is false .

This is my code so far:

abstract ERC20 {
    function _transfer(
        address _from,
        address _to,
        uint256 _value
    ) internal {}

    function transfer(address _to, uint256 _value)
        public
        returns (bool success)
    {
        _transfer(msg.sender, _to, _value);
        return true;
    }
}

contract ERC1155 {
    function buyNFT(uint256 _NFTPrice, address _to)
        public
        returns (bytes memory)
    {
        (bool success, bytes memory returnData) = 0x00...00.delegatecall(
            abi.encodeWithSelector(HRC20.transfer.selector, _to, _NFTPrice)
        );

        if (!success) {
            if (returnData.length == 0) revert("here");

            assembly {
                revert(add(32, returnData), mload(returnData))
            }
        }

        return returnData;
    }

}

Sorry for no code highlight, it seems stack overflow doesn't support the .sol extension.

Also, I've tried using abi.encodePacked() , abi.encode() , abi.encodeWithSignature() .

Answer 1

As @bbbbbbbbb had commented, the transaction flow would be:
1 - user calls approve function on ERC20 smart contract, passing the address of ERC1155 and the NFT price;
2 - user calls the buyNFT function on ERC1155 which will call the transferFrom function of ERC20 ;
3 - In this way, the tokens are debited from the user's account and credited to the ERC1155 contract, thus requiring a function to withdraw these payments.

The drawback is that the user needs to sign two transactions to buy the NFT when the used currency to sell it isn't the network token.

The final code would be:

interface ERC20 {
    function transferFrom(
        address _from,
        address _to,
        uint256 _value
    ) internal {}
}

contract ERC1155 {
    ERC20 erc20Contract = ERC20(0x1234...5678);

    function buyNFT(uint256 price)
        external
    {
        erc20Contract.transferFrom(msg.sender, price);
        // I'm assuming the `transferFrom` will revert if user
        // doesn't have sufficient balance, otherwise, we would need to check
        // for the return value and revert if needed

       _mint(msg.sender, tokenId, quantity);
    }

}