How to use DAI in my contract

Question

I'm familiar with smart contracts development. Although, every time I developed something, I used traditional ether. For the sake of simplicity, let's assume this contract.

pragma solidity ^0.5.0;

contract  Example {

    constructor () public {}

    function () external payable {}

    function getBalance() public view returns (uint256) {
        return address(this).balance;
    }

    function withdraw() public {
        msg.sender.transfer(address(this).balance);
    }
}

How do I take this exact contract and simply allow it to do exactly the same, but using DAI instead? Please be practical, I read a lot of theory stuff already, I'm just looking to the actual code on how to do this.

Answer 1

        pragma solidity ^0.5.0;

        //import ERC20 functionality ...

        contract  Example {

            ERC20   public token;

            //@param _token the address of the DAI smart contract
            constructor(ERC20 _token) public {
                token = ERC20(_token);
            }

            function () external payable {}

            function getBalance() public view returns (uint256) {
                return token.balanceOf(address(this));
            }

            function withdraw() public {
                token.transfer(msg.sender, getBalance());
            }
        }

You've already read a lot of theory, so here's a practical example of your exact code but using DAI instead of ether, hope it helps.