NFT(非同质化代币):类似于明朝、宋朝的青花瓷。虽然都是青花瓷。但是都具有唯一的典藏价值。而且价值可能不同。 NFT就是具有唯一价值的代币。
ERC721: 是以太坊规定实现NFT的一种标准了。实现ERC21标准的智能合约就是NFT代币了。
1.接口
1.ERC721
定义接口参考：ERC 721 – OpenZeppelin 文档
下面是以太坊官方定义的标准,由于就是我写的代码运行环境不支持payable关键字，因此我打算围绕官方接口定义，按照自己要求稍微增删一下。
pragma solidity ^0.4.25;interface ERC721 {/// Event///event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId);event Approval(address indexed _owner, address indexed _approved, uint256 indexed _tokenId);event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);/// Function///function balanceOf(address _owner) external view returns (uint256); // 返回所有者代币的总个数function ownerOf(uint256 _tokenId) external view returns (address); // 返回代币id对应所有者的账户地址// 安全的转账//_to:是已经被指定 id 代币的所有者授予的账户 and (接受者不是智能合约 or 接受者实现ERC721Receiver接口的智能合约// 将给定id的代币转移到接受者账户// data是元数据，可有可不有(我觉得)function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external; function safeTransferFrom(address _from, address _to, uint256 _tokenId) external;// 这个转账对比上述安全转账(少了一个接受者地址实现是否是ERC721Receiver接口的智能合约地址的判断)function transferFrom(address _from, address _to, uint256 _tokenId) external;// 授权将代币转移到另一个账户的权限function approve(address _approved, uint256 _tokenId) external;// 授权接受者使用所有代币function setApprovalForAll(address _operator, bool _approved) external;// 返回授权指定id 代币的接受者账户function getApproved(uint256 _tokenId) external view returns (address);// 判断某账户代币的拥有者是否能被某账户全部使用function isApprovedForAll(address _owner, address _operator) external view returns (bool);}2.ERC721Metadata
以下就是ERC21的元数据接口，这是可选地。名称、标识符、每一个token对应的tokenURI。
pragma solidity ^0.4.25;interface ERC721Metadata {function name() external view returns (string);function symbol() external view returns (string);function tokenURI(uint256 tokenId) external view returns (string); // 返回指定id的代币所对对应的uri}3.ERC721Enumerable
另一个额外的可选接口是枚举， 它包含了按索引获取到对应的代币。
pragma solidity ^0.4.25;interface ERC721Enumerable {// 确定合约当前全部的nft数量(出去销毁)function totalSupply() external view returns (uint256);// 从代币列表返回第n个代币function tokenByIndex(uint256 _index) external view returns (uint256);// 返回所有者代币列表的第n个代币function tokenOfOwnerByIndex(address _owner, uint256 _index) external view returns (uint256);}4.ERC721Receiver
pragma solidity ^0.4.25;// 资产合约interface ERC721Receiver {function onERC721Received(address operator, address from, uint256 tokenId, bytes data) externalreturns (bytes);}2.实现
1.Jzm721
这是我针对ERC721接口的合约实现。基本满足官方接口标准。
pragma solidity ^0.4.25;import "./ERC721.sol";import "./ERC721Metadata.sol";contract Jzm721 is ERC721,ERC721Metadata {/// Filed///string public name;string public symbol;uint256nftCount;mapping (address => uint[])balanceMap; // owner => tokenId[]mapping (uint256=>string)tokenURIMap; // tokenId => tokenURImapping (uint256=>address)tokenIdMap; // tokenId => ownermapping (uint256 => address) approveMap; // tokenId => operator(经营方)mapping (address=>mapping (address=>bool)) approveAllMap; // operator =>(owner => true/false)/// Function///constructor(string memory _name,string memory _symbol) public {name = _name;symbol = _symbol;}function name() external view returns (string) {return name;}function symbol() external view returns (string) {return symbol;}function tokenURI(uint256 tokenId) external view returns (string) {return tokenURIMap[tokenId];}// 创建代币function mint(address _owner,string _tokenURI) externalreturns (uint256) {require(_owner != address(0),"owner is not empty address!");uint256 tokenId = _mint(_owner);_setTokenURI(tokenId, _tokenURI);return tokenId;}function balanceOf(address _owner) external view returns (uint256) {return balanceMap[_owner].length;}function ownerOf(uint256 _tokenId) external view returns (address) {return tokenIdMap[_tokenId];}// 这里我忽略了data这个元数据的作用function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external {_transferFrom(_from, _to, _tokenId);if(_isContractAdd(_to)) {if(_checkIfFunctionExists(_to)) {_externalTransfer(_from, _to, _tokenId);emit Transfer(_from, _to, _tokenId);}}}function safeTransferFrom(address _from, address _to, uint256 _tokenId) external {_transferFrom(_from, _to, _tokenId);if(_isContractAdd(_to)) {if(_checkIfFunctionExists(_to)) {_externalTransfer(_from, _to, _tokenId);emit Transfer(_from, _to, _tokenId);}}}function transferFrom(address _from, address _to, uint256 _tokenId) external {_transferFrom(_from, _to, _tokenId);}function approve(address _approved, uint256 _tokenId) external {require(_approved != address(0),"approved is not empty address!");address owner = msg.sender;approveMap[_tokenId] = _approved; emit Approval(owner,_approved,_tokenId);}function setApprovalForAll(address _operator, bool _approved) external {require(_operator != address(0),"operator is not empty address!");address owner = msg.sender;approveAllMap[_operator][owner] = _approved;emitApprovalForAll(owner,_operator,_approved);}function getApproved(uint256 _tokenId) external view returns (address) {return _getApproved(_tokenId);}function isApprovedForAll(address _owner, address _operator) external view returns (bool) {return _isApprovedForAll(_owner,_operator);}function _checkIfFunctionExists(address _add)publicreturns (bool) {bytes4 functionSelector = bytes4(keccak256("onERC721Received(address,address,uint256,bytes)")); // 函数选择器，基础原型前4个字节bytes memory data = abi.encodeWithSelector(functionSelector, address(0),address(0),0,"");bool success = _add.call(data);return success;}function _transferFrom(address _from, address _to, uint256 _tokenId) private {// from不能是零地址。require(_from != address(0),"from is not empty address!");// to不能是零地址。require(_to != address(0),"from is not empty address!");// tokenId令牌必须存在并由from拥有。require(tokenIdMap[_tokenId] == _from,"The tokenIdmust exist and be owned by from!");// 接受者一方不是合约地址if (!_isContractAdd(_to)) {if (_isApproved(_from, _to, _tokenId)) { // TODO_externalTransfer(_from, _to, _tokenId);emit Transfer(_from, _to, _tokenId);}}}function _externalTransfer(address _from,address _to,uint256 _tokenId) private {// 删除代币批准if(_getApproved(_tokenId) == _to) {approveMap[_tokenId] = address(0); }// 转账_deleteAccountToken(_from,_tokenId);tokenIdMap[_tokenId] = _to;balanceMap[_to].push(_tokenId);}function _deleteAccountToken(address _owner,uint256 _tokenId) private {uint256[] storage tokenIds = balanceMap[_owner];uint len =tokenIds.length;for (uint i = 0; i 0;}function _getApproved(uint256 _tokenId) private view returns(address) {return approveMap[_tokenId];}function _isApproved(address _owner, address _operator,uint256 _tokenId) private view returns (bool) {bool approved = _getApproved(_tokenId) == _operator;return approved || _isApprovedForAll(_owner, _operator);}function _isApprovedForAll(address _owner, address _operator) private view returns(bool) {return approveAllMap[_operator][_owner];}}2.Jzm721Receiver
在这里我就是想要满足合约地址的合约实现ERC721Receiver接口的标准。原合约，这里该函数涉及代币的转账，由于环境的原因，不支持payable关键字，我这里是无法满足的。
pragma solidity ^0.4.25;import "./ERC721Receiver.sol";contract Jzm721Receiver is ERC721Receiver {function onERC721Received(address operator, address from, uint256 tokenId, bytes data) externalreturns (bytes) {return data;}}