ERC20 Tokens – How to Build an Abstract Contract for Users to Claim Tokens

allowanceerc-20solidity

My goal is to build an abstract contract and send a specific erc20 token into it so that others can claim the erc20token with merkletree validations.
However I am having problem approving the contract to spend this erc20. Here is my claiming function. Please help me figure out how to assign allowance or otherwise. Is there a walk-around to achieve the goal ?

function claimTokens(IERC20 _token, uint256 amount, bytes32[] calldata merkleProof) public {
        uint256 erc20balance = _token.balanceOf(address(this));
        require(amount <= erc20balance, "balance is low");
        bytes32 leaf = keccak256(abi.encodePacked(msg.sender, amount));
        bool valid = MerkleProof.verify(merkleProof, merkleRoot, leaf);
        require(valid, "Chimpz: Valid proof required.");
        require(!claimed[msg.sender], "Tokens already claimed.");
        claimed[msg.sender] = true;
    
        emit Claim(msg.sender, amount);
        _token.transferFrom(address(this), msg.sender, amount);
    }

Best Answer

You should be able to transfer tokens via the transfer() function:

 function transfer(address recipient, uint amount) external returns (bool);

Transfer does not require approval.

Related Solutions

Solidity – Handling Unimplemented Functions in Contracts

The problem is that totalSupply() implementation is missing. Seems like autogenerated getters do not count. So you need to explicitly create the function.

contract StandardToken is Token {
    uint256 _totalSupply;

    function totalSupply() constant returns (uint256 totalSupply) {
        totalSupply = _totalSupply;
    }
}

erc-20 – How to Resolve ERC20: Insufficient Allowance Error

msg.sender will have to approve GameItem smart contract address before transferFrom can be initialized to work, you were trying to transfer from the sender and the sender is yet to approve the contract address it won't work, the declaration that you here

GXGToken.approve(msg.sender,_amount);

GXGToken token has an approve function, the user must interact with GXGToken token contract address direct and use it approval function to approve GameItem smart contract address before the user (address) before the user(address) will call the function.

approve(GameItem smart contract address, _amount);

your intention was that it would automatically set the msg.sender to approve the GameItem smart contract address, it doesn't work that way.

the solution here can explain the use case of Approval and transferFrom excplicitly: What is the use case of transferFrom function in ERC20 token contract?

Best Answer

Related Solutions

Solidity – Handling Unimplemented Functions in Contracts

erc-20 – How to Resolve ERC20: Insufficient Allowance Error

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