TRC-721

TRC-721 is a set of standard interfaces, for issuing non-fungible tokens(NFT) on the TRON network. TRC-721 is fully compatible with ERC-721.

TRC-721 Smart Contract Interface Implementation

Every TRC-721 compliant contract must implement the TRC721 and TRC165 interfaces. Other extension interfaces can be implemented according to specific business requirements.

TRC-721 & TRC-165 Interfaces

Solidity

pragma solidity ^0.4.20;​  interface TRC721 {    // Returns the number of NFTs owned by the given account    function balanceOf(address _owner) external view returns (uint256);​    //Returns the owner of the given NFT    function ownerOf(uint256 _tokenId) external view returns (address);​    //Transfer ownership of NFT    function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external payable;​    //Transfer ownership of NFT    function safeTransferFrom(address _from, address _to, uint256 _tokenId) external payable;​    //Transfer ownership of NFT    function transferFrom(address _from, address _to, uint256 _tokenId) external payable;​    //Grants address ‘_approved’ the authorization of the NFT ‘_tokenId’    function approve(address _approved, uint256 _tokenId) external payable;​    //Grant/recover all NFTs’ authorization of the ‘_operator’    function setApprovalForAll(address _operator, bool _approved) external;​    //Query the authorized address of NFT    function getApproved(uint256 _tokenId) external view returns (address);​    //Query whether the ‘_operator’ is the authorized address of the ‘_owner’    function isApprovedForAll(address _owner, address _operator) external view returns (bool);​    //The successful ‘transferFrom’ and ‘safeTransferFrom’ will trigger the ‘Transfer’ Event    event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId);​    //The successful ‘Approval’ will trigger the ‘Approval’ event    event Approval(address indexed _owner, address indexed _approved, uint256 indexed _tokenId);​    //The successful ‘setApprovalForAll’ will trigger the ‘ApprovalForAll’ event    event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);​  }​  interface TRC165 {      //Query whether the interface ‘interfaceID’  is supported      function supportsInterface(bytes4 interfaceID) external view returns (bool);  }

A wallet/broker/auction application MUST implement the wallet interface if it will accept safe transfers.Solidity

interface TRC721TokenReceiver {     //This method will be triggered when the ‘_to’ is the contract address during the ‘safeTransferFrom’ execution, and the return value must be checked, If the return value is not bytes4(keccak256("onTRC721Received(address,address,uint256,bytes)")) throws an exception. The smart contract which can receive NFT must implement the TRC721TokenReceiver interface.       function onTRC721Received(address _operator, address _from, uint256 _tokenId, bytes _data) external                returns(bytes4);   }

🚧Note

The hash of bytes4(keccak256("onTRC721Received(address,address,uint256,bytes))) is different from the Ethereum version bytes4(keccak256("onERC721Received(address,address,uint256,bytes))). Please use 0x5175f878 instead of 0x150b7a02.

1.1.2 OPTIONAL Metadata Extension Interface

The metadata extension is OPTIONAL for TRC-721 smart contracts. This allows your smart contract to be interrogated for its name and for details about the assets which your NFTs represent.Solidity

interface TRC721Metadata {     //Return the token name     function name() external view returns (string _name);​      //Return the token symbol     function symbol() external view returns (string _symbol);​       //Returns the URI of the external file corresponding to ‘_tokenId’. External resource files need to include names, descriptions and pictures.      function tokenURI(uint256 _tokenId) external view returns (string);  }

URI is a URI link describing the _tokenId asset, pointing to a JSON file that conforms to the TRC721 metadata description structure. When tokens are minted, each token needs to be assigned a unique URI:JSON

{    "title": "Asset Metadata",    "type": "object",    "properties": {        "name": {            "type": "string",            "description": "Identifies the asset to which this NFT represents"        },        "description": {            "type": "string",            "description": "Describes the asset to which this NFT represents"        },        "image": {            "type": "string",            "description": "A URI pointing to a resource with mime type image/* representing the asset to which this NFT represents. Consider making any images at a width between 320 and 1080 pixels and aspect ratio between 1.91:1 and 4:5 inclusive."        }    }}

1.1.3 OPTIONAL Enumeration Extension Interface

The enumeration extension is OPTIONAL for TRC-721 smart contracts. This allows your contract to publish its full list of NFTs and make them discoverable.Solidity

interface TRC721Enumerable  {    //Return the total supply of NFT    function totalSupply() external view returns (uint256);​    //Return the corresponding ‘tokenId’ through ‘_index’    function tokenByIndex(uint256 _index) external view returns (uint256);​     //Return the ‘tokenId’ corresponding to the index in the NFT list owned by the ‘_owner'    function tokenOfOwnerByIndex(address _owner, uint256 _index) external view returns (uint256);  }