導言

本次範例參考ERC721協議，ERC721協議和ERC20所使用的FUNCTION很相似，差別在於ERC721為NFT(Non-Fegible Token)不可替代的代幣、ERC20為FT(Fegible Token)可替代的代幣，ERC20適合的應用包含股票、金錢、賭博遊戲，那ERC721比較偏向於收藏、卡牌收集，像是加密貓就是ERC721最著名的一個範例。

ERC721 reference

程式碼

pragma solidity^0.4.25;
contract ERC721_interface{
    event Transfer(address indexed _from,address indexed _to,uint256 _tokenId);
    event Approval(address indexed _owner,address indexed _approved,uint256 _tokenId);
    event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);
    function balanceOf(address _owner)public view returns(uint256);
    function ownerOf(addrss _tokenId)public view returns(address);
    function safeTransferFrom(address _from,address _to, uint256 _tokenId) public;
    function safeTransferFrom(address _from,address _to, uint256 _tokenId , bytes data) public;
    function transferFrom(address _from,address _to, uint256 _tokenId) public;
    function approve(address _to,uint256 _tokenId)public;
    function setApprovalForAll(address _operator, bool _approved) public;
    function getApproved(uint256 _tokenId) public view returns(address);
    function isApprovedForALL(address _owner, address _operator) public view reutrns(bool);
    function onERC721Received(address _operator, address _from, uint256 _tokenId, bytes _data)public returns(bytes4);
}

contract ERC721 is ERC721_interface{ 
    mapping(uint256=>address) public tokenOwner;
    mapping(uint256=>address) public tokenApproval;
    mapping(address=>uint256) public ownerTokenCount;
    mapping(address=>mapping(address=>bool)) public operatorApproval;
    mapping(uint256=>bool) public tokenExists;


    function balanceOf(address _owner) public view returns(uint256 tokenCount){
        require(owner != address(0),"無效的address");
        return ownerTokenCount[_owner];
    }

    function ownerOf(uint256 _tokenId) public view returns(address owner){
        return  tokenOwner[_tokenId];
    }
    function addToken(uint256 _tokenId) public{
        require(tokenOwner[_tokenId] == address(0));
        tokenOwner[_tokenId] = msg.sender;
        ownerTokenCount[msg.sender]++;
    }
    //執行轉移token所有權
    function transferFrom(address _from,address _to, uint256 _tokenId) public{
        address owner = tokenOwner[_tokenId];
        require(operatorApproval[owner][msg.sender] ,"你沒有被賦予代替操作的權利");
        require( owner == _from,"持有者身分不符合");
        require( _to != address(0),"無效的address");
        require(tokenExists[_tokenId],"沒有這個token");

        tokenApproval[_tokenId] = address(0);
        tokenOwner[_tokenId] = _to;
        ownerTokenCount[_from]--;
        ownerTokenCount[_to]++;
        emit Transfer(_from,_to,_tokenId);
    }

    //確定轉移token所有權給指定的address
    function approve(address _to, uint256 _tokenId) public{
        address owner = tokenOwner[_tokenId];
        require(_to != address(0),"無效的address");
        require(msg.sender == owner || operatorApproval[owner][msg.sender] ,"你不是持有者也沒有代替操作的權利");
        
        tokenApproval[_tokenId] = _to;
        emit Approval(msg.sender,_to,_tokenId);
    }

    //決定是否給予operator行為操作權
    function setApprovalForAll(address _operator, bool _approved) public{
        require(_operator != address(0),"無效的address");

        operatorApproval[msg.sender][_operator] = _approved;
        emit ApprovalForAll(msg.sender,_operator,_approved);
    }

    //確定tokenID的持有者是誰
    function getApproved(uint256 _tokenId) public view returns(address){
        require(tokenExists[_tokenId],"沒有這個token");
        return tokenApproval[_tokenId];
    }

    //確定operator可以代表owner的行為
    function isApprovedForALL(address _owner, address _operator) public view reutrns(bool){
        return operatorApproval[_owner][_operator];
    }

    
}

解說

(待補)