USDT批准和转让失败

Question

我已经制定了一项明智的合同，允许人们使用加密货币，并在稍后的日期得到一个令牌。

(顺便提一下，我从帕特里克·柯林斯的第一本Freecodecamp教程-确切地说是第13课)中学到了很多灵感。

这对于USDC、WETH和DAI很好--但是，当我尝试使用USDT时，我会得到以下错误：

我不太清楚为什么USDT不起作用(注意，我也解释了USDT是6小数位的事实)。

作为参考，以下是我的智能合同：

// SPDX-License-Identifier: MIT

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";

pragma solidity ^0.8.0;

contract TokenFarm is Ownable, ReentrancyGuard {
    mapping(address => mapping(address => uint256)) public stakingBalance;
    mapping(address => uint256) public uniqueTokensStaked;
    mapping(address => address) public tokenPriceFeedMapping;
    address[] public stakers;
    address[] public allowedTokens;
    IERC20 public timeToken;
    uint256 public totalRaised;
    uint256 public goal;
    enum FUND_STATE {
        OPEN,
        REFUND,
        CLOSED
    }
    FUND_STATE public fund_state;

    constructor(address _timeTokenAddress) public {
        timeToken = IERC20(_timeTokenAddress);
        fund_state = FUND_STATE.OPEN;
        goal = 175000000000000000000000;
    }

    function stateOpen() public onlyOwner {
        fund_state = FUND_STATE.OPEN;
    }

    function stateRefund() public onlyOwner {
        fund_state = FUND_STATE.REFUND;
    }

    function stateClosed() public onlyOwner {
        fund_state = FUND_STATE.CLOSED;
    }

    function setPriceFeedContract(address _token, address _priceFeed)
        public
        onlyOwner
    {
        tokenPriceFeedMapping[_token] = _priceFeed;
    }

    function goalAmount() public onlyOwner returns (uint256) {
        return goal;
    }

    function totalERCRaised() public onlyOwner returns (uint256) {
        return totalRaised;
    }

    function getTokenValue(address _token)
        public
        view
        returns (uint256, uint256)
    {
        address priceFeedAddress = tokenPriceFeedMapping[_token];
        AggregatorV3Interface priceFeed = AggregatorV3Interface(
            priceFeedAddress
        );
        (, int256 price, , , ) = priceFeed.latestRoundData();
        uint256 decimals = uint256(priceFeed.decimals());
        return (uint256(price), decimals);
    }

    function stakeTokens(uint256 _amount, address _token) public nonReentrant {
        require(fund_state == FUND_STATE.OPEN);
        require(_amount > 0, "Amount must be more than zero!");
        require(tokenIsAllowed(_token), "Token is currently not allowed!");
        (uint256 price, uint256 decimals) = getTokenValue(_token);
        require(
            totalRaised + ((_amount * price) / ((10**decimals))) < goal,
            "Too much money"
        );
        uint256 _amount2 = ((_amount * (10**20)) / (10**decimals));
        IERC20(_token).transferFrom(msg.sender, address(this), _amount);
        updateUniqueTokensStaked(msg.sender, _token);
        if (
            address(_token) ==
            address(0x07865c6E87B9F70255377e024ace6630C1Eaa37F)
        ) {
            stakingBalance[_token][msg.sender] =
                stakingBalance[_token][msg.sender] +
                _amount2;
            totalRaised = uint256(
                totalRaised + (((_amount2 * price)) / ((10**decimals)))
            );
        }
        if (
            address(_token) ==
            address(0x509Ee0d083DdF8AC028f2a56731412edD63223B9)
        ) {
            stakingBalance[_token][msg.sender] =
                stakingBalance[_token][msg.sender] +
                _amount2;
            totalRaised = uint256(
                totalRaised + (((_amount2 * price)) / ((10**decimals)))
            );
        }
        if (
            address(_token) ==
            address(0xBA62BCfcAaFc6622853cca2BE6Ac7d845BC0f2Dc)
        ) {
            stakingBalance[_token][msg.sender] =
                stakingBalance[_token][msg.sender] +
                _amount;
            totalRaised = uint256(
                totalRaised + (((_amount * price)) / ((10**decimals)))
            );
        }
        if (
            address(_token) ==
            address(0x60D4dB9b534EF9260a88b0BED6c486fe13E604Fc)
        ) {
            stakingBalance[_token][msg.sender] =
                stakingBalance[_token][msg.sender] +
                _amount;
            totalRaised = uint256(
                totalRaised + (((_amount * price)) / ((10**decimals)))
            );
        }
        if (uniqueTokensStaked[msg.sender] == 1) {
            stakers.push(msg.sender);
        }
    }

    function issueTokens() public onlyOwner nonReentrant {
        require(fund_state == FUND_STATE.OPEN);
        for (
            uint256 stakersIndex = 0;
            stakersIndex < stakers.length;
            stakersIndex++
        ) {
            address recipient = stakers[stakersIndex];
            uint256 userTotalValue = getUserTotalValue(recipient);
            timeToken.transfer(recipient, userTotalValue);
        }
    }

    function claimRefund(address _token) public nonReentrant {
        require(fund_state == FUND_STATE.REFUND);
        uint256 balance = stakingBalance[_token][msg.sender];
        require(balance > 0, "Staking balance cannot be zero!");
        IERC20(_token).transfer(msg.sender, balance);
        stakingBalance[_token][msg.sender] = 0;
        uniqueTokensStaked[msg.sender] = uniqueTokensStaked[msg.sender] - 1;
    }

    function getUserTotalValue(address _user) public view returns (uint256) {
        uint256 totalValue = 0;
        require(uniqueTokensStaked[_user] > 0, "No tokens staked!");
        for (
            uint256 allowedTokensIndex = 0;
            allowedTokensIndex < allowedTokens.length;
            allowedTokensIndex++
        ) {
            totalValue =
                totalValue +
                getUserSingleTokenValue(
                    _user,
                    allowedTokens[allowedTokensIndex]
                );
        }
        return totalValue;
    }

    function getUserSingleTokenValue(address _user, address _token)
        public
        view
        returns (uint256)
    {
        if (uniqueTokensStaked[_user] <= 0) {
            return 0;
        }
        (uint256 price, uint256 decimals) = getTokenValue(_token);
        return ((stakingBalance[_token][_user] * price) / (10**decimals));
    }

    function withdrawToken(address _token, uint256 _amount)
        external
        onlyOwner
        nonReentrant
    {
        IERC20 token = IERC20(_token);
        token.transfer(msg.sender, _amount);
    }

    function updateUniqueTokensStaked(address _user, address _token) internal {
        if (stakingBalance[_token][_user] <= 0) {
            uniqueTokensStaked[_user] = uniqueTokensStaked[_user] + 1;
        }
    }

    function addAllowedTokens(address _token) public onlyOwner {
        allowedTokens.push(_token);
    }

    function tokenIsAllowed(address _token) public view returns (bool) {
        for (
            uint256 allowedTokensIndex = 0;
            allowedTokensIndex < allowedTokens.length;
            allowedTokensIndex++
        ) {
            if (allowedTokens[allowedTokensIndex] == _token) {
                return true;
            }
        }
        return false;
    }
}

我非常感谢任何和所有的帮助，因为这已经困扰了我一段时间了！

Answer 1

在四处搜寻之后，我发现了这个：

As described in Tether code: To change the approve amount you first have to reduce the addresses allowance to 0 calling approve(spender, 0)

你查过这个了吗？

Answer 2

可以通过在调用批准函数之前将上一次批准设置为0来完成这一任务。