You can use the code below as a reference:
pragma solidity 0.4.25;
// Import OpenZeppelin's ERC20 interface defenition
import "https://github.com/OpenZeppelin/openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";
import "https://github.com/OpenZeppelin/openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";
// Simple ERC20 token that mints the given initialSupply to the deployer
// For testing purposes
contract MyToken is ERC20 {
string public name = "MyToken";
string public symbol = "MYT";
uint256 public decimals = 18;
uint256 private _totalSupply;
mapping (address => uint256) private _balances;
constructor(uint256 _intialSupply) public {
_totalSupply = _intialSupply;
_balances[msg.sender] = _intialSupply;
}
}
// Contract that uses any ERC20 token
contract UsingERC20 {
IERC20 public associatedToken;
// Constructor. Pass it the token you want this contract to work with
constructor(IERC20 _token) public {
associatedToken = _token;
}
function doSomethingThatRequiresERC20tokens() public {
// The key here is to use ERC20's transferFrom method.
// For this to work, the given address has to have enough balance,
// and it has to allow this contract to transfer tokens from their account.
// This can be done using ERC20's approve method/
// If transferFrom fails, the transaction reverts. So if the transaction
// does not revert, we know that the transer succeeded.
// Using msg.sender here, the caller of this function.
// Could be any address you like, though.
// This transfers 100 tokens from msg.sender to this contract.
associatedToken.transferFrom(msg.sender, address(this), 100);
// Ok, now the tokens are transferred successfully, let's do some cool stuff!
emit YayIReceivedTokens(100, msg.sender, associatedToken.balanceOf(address(this)));
}
event YayIReceivedTokens(uint256 amount, address fromAccount, uint256 totalBalance);
}
