3

Let's say you've created and issued an ERC20 token. You then create a crowdsale and only want to accept the token you issued, not Ethereum.

Is this possible?

2

If you control both token and crowdsale it can be done easily

contract Token {

    address officialCrowdsale;

    function investCrowdsale(uint256 _value, bytes _extraData) returns (bool success) {
        allowance[msg.sender][officialCrowdsale] = _value;     
        Crowdsale crowdsale = Crowdsale(officialCrowdsale);
        crowdsale.investFromToken(msg.sender, _value, _extraData);
        return true; 
    }

}

And in your crowdsale

contract Crowdsale {

    address officialToken;
    address depositToken;

    function investFromToken(address _from, uint256 _value ,bytes _extraData) returns (bool success) {
        if (msg.sender != officialToken) throw; // only accept transfer from the official token
        Token token = Token(_token);
        token.transferFrom(_from, depositToken, _value); // store tokens in deposit
        DoInvest(_value, _extraData); // Do the investment
        return true; 
    }

}

If your token is already deployed and has support for approveAndCall you can do something similar.

  • I already created the token using the tutorial code. How would I alter the crowdsale tutorial code to make it accept my token? (I've also already created the shareholder's association with my token) – DMC Jul 22 '17 at 16:08
  • Please add a link to your token source to the question if it is already deployed. There's no generic solution that will work for every token. – Ismael Jul 22 '17 at 20:43
2

An alternative solution could be this: first of all, the user should call the approve() function of your ERC-20 token, passing as parameters the crowdsale contract and the amount he wants to spend in the crowdsale:

approve(crowdsaleAddress, amount)

then in your crowdsale contract, you should first check the user's balance and then tranfer the amount to your crowdsale address.

You crowdsale contract:

    //interface to your Token
    contract YourToken{
        function transferFrom(address _from, address _to, uint _value) returns (bool success);
        function approve(address _spender, uint _value) returns (bool success);
        function balanceOf(address _owner) constant returns (uint balance);
    }


    contract Crowdsale {

        address owner;  
        mapping(address => uint256) balances;
        function Crowdsale(){
            owner = msg.sender;
        }

        function acceptOnlyMyToken(address _yourTokenAddress, uint256 amount){
            address user = msg.sender;
            YourToken token = YourToken(_yourTokenAddress);

            //get the user's balance
            uint256 userBalance = token.balanceOf(user);
            //check user's balance
            if(userBalance >= amount){      
                token.transferFrom(user, owner, amount);        

            }

        }

    }

I asked a similar question: Best practices for interacting with other contracts

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