假设有个合约ERC20充值方法，方法接收msg.sender发送的ERC20代币，并增加合约中的余额统计
import "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";
...
function rechargeMain(address mainChainErc20Addr, uint256 amount) payable external notContract returns (bool){
...
require(amount > 0, "The recharge amount is too small");
require(IERC20(mainChainErc20Addr).balanceOf(msg.sender) >= amount, "Insufficient contract account balance");
IERC20(mainChainErc20Addr).transfer(address(this), amount);
...
return true;
}
执行后提示
execution reverted: ERC20: transfer amount exceeds balance
经测试（Github Code）
function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
_transfer(_msgSender(), recipient, amount);
return true;
}
_msgSender()的地址为合约地址，测试交易（跳转地址）
所以我们需要使用transferFrom，代码修改为
import "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";
...
function rechargeMain(address mainChainErc20Addr, uint256 amount) payable external notContract returns (bool){
...
require(amount > 0, "The recharge amount is too small");
require(IERC20(mainChainErc20Addr).balanceOf(msg.sender) >= amount, "Insufficient contract account balance");
IERC20(mainChainErc20Addr).transferFrom(msg.sender, address(this), amount);
...
return true;
}
执行完，提示
execution reverted: ERC20: transfer amount exceeds allowance
查看代码（Github code）
function transferFrom(
address sender,
address recipient,
uint256 amount
) public virtual override returns (bool) {
_transfer(sender, recipient, amount);
uint256 currentAllowance = _allowances[sender][_msgSender()];
require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
unchecked {
_approve(sender, _msgSender(), currentAllowance - amount);
}
return true;
}
需要先批准交易金额（津贴）（Github Code）
function approve(address spender, uint256 amount) public virtual override returns (bool) {
_approve(_msgSender(), spender, amount);
return true;
}
查看当前剩余允许值，（Github Code）
function allowance(address owner, address spender) public view virtual override returns (uint256) {
return _allowances[owner][spender];
}
也可以执行increaseAllowance或decreaseAllowance增量增减调整
对于此次需求，执行rechargeMain前，需要先执行津贴充值
increaseAllowance(address spender, uint256 addedValue)
执行increaseAllowance的地址为当前充值转出地址
spender为当前转入合约地址
addedValue为当前充值金额
测试交易：https://ropsten.etherscan.io/tx/0x0f65cb2a7ca2bf0d6b1fdd65e943afb5c6305573dc3c3a960c2f86f71757c897
