Protocol Interface
Protocol Interface
TRC-721 Standard
A standard interface allows applications to track and transfer NFTs on Tron. Simple TRC-721 smart contracts list as below to track a large number of NFTs. TRC-20 token standard is insufficient for handling NFTs due to each token in TRC-721 being unique. The standard of TRC-721 is inspiring on Tron. It plays an important role as well as TRC-20.
MUST Implemented Interfaces
Every TRC-721 compliant contract must implement the TRC721 and TRC165 interfaces
pragma solidity ^0.4.20;
interface TRC721 {
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 balanceOf(address _owner) external view returns (uint256);
function ownerOf(uint256 _tokenId) external view returns (address);
function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external payable;
function safeTransferFrom(address _from, address _to, uint256 _tokenId) external payable;
function transferFrom(address _from, address _to, uint256 _tokenId) external payable;
function approve(address _approved, uint256 _tokenId) external payable;
function setApprovalForAll(address _operator, bool _approved) external;
function getApproved(uint256 _tokenId) external view returns (address);
function isApprovedForAll(address _owner, address _operator) external view returns (bool);
}
interface TRC165 {
function supportsInterface(bytes4 interfaceID) external view returns (bool);
}
balanceOf(address _owner)
Returns the number of NFTs owned by the specified account
ownerOf(uint256 _tokenId)
Returns the owner of the specified NFT
safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data)
Transfer ownership of an NFT
safeTransferFrom(address _from, address _to, uint256 _tokenId)
Transfer ownership of an NFT
transferFrom(address _from, address _to, uint256 _tokenId)
Transfer the ownership of an NFT (the caller must confirm whether the _to address can receive the NFT normally, otherwise the NFT will be lost)
approve(address _approved, uint256 _tokenId)
Grant other people control of an NFT
setApprovalForAll(address _operator, bool _approved)
Grant/recover control of all NFTs by a third party (_operator)
getApproved(uint256 _tokenId)
Query the authorization of a certain NFT
isApprovedForAll(address _owner, address _operator)
Query whether the operator is the authorized address of the owner
supportsInterface(bytes4 interfaceID)
Query whether a certain interface is supported (interfaceID)
event Approval(address indexed _owner, address indexed _approved, uint256 indexed _tokenId)
Approval event will be triggered after Approval is successful
event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId)
Successful transferFrom and safeTransferFrom will trigger the Transfer event
event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved)
ApprovalForAll event will be triggered after setApprovalForAll succeeds
A wallet/broker/auction application MUST implement the wallet interface if it will accept safe transfers.
interface TRC721TokenReceiver {
function onTRC721Received(address _operator, address _from, uint256 _tokenId, bytes _data) external returns(bytes4);
}
onTRC721Received(address _operator, address _from, uint256 _tokenId, bytes _data)
Works with the safeTransferFrom
method, when _to is the contract address, you need to call this method and check the return value. If the return value is not bytes4(keccak256("onTRC721Received(address,address,uint256,bytes)")) an exception will be thrown. A smart contract that can receive NFT must implement the TRC721TokenReceiver interface.
Note
The hash of bytes4(keccak256("onTRC721Received(address,address,uint256,bytes))) is different from the Ethereum version bytes4(keccak256("onERC721Received(address,address,uint256,bytes))). With the return value of function
onTRC721Received
, please use 0x5175f878 instead of 0x150b7a02.
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.
interface TRC721Metadata {
function name() external view returns (string _name);
function symbol() external view returns (string _symbol);
function tokenURI(uint256 _tokenId) external view returns (string);
}
name()
Returns the contract name
symbol()
Returns the contract symbol
tokenURI(uint256 _tokenId)
Returns the URI of the external file corresponding to _tokenId. External resource files need to include names, descriptions and pictures.
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.
interface TRC721Enumerable {
function totalSupply() external view returns (uint256);
function tokenByIndex(uint256 _index) external view returns (uint256);
function tokenOfOwnerByIndex(address _owner, uint256 _index) external view returns (uint256);
}
totalSupply()
Returns the total amount of NFT
tokenByIndex(uint256 _index)
Returns the corresponding tokenId through _index
tokenOfOwnerByIndex(address _owner, uint256 _index)
Returns the tokenId corresponding to the index in the NFT list owned by the owner
Updated almost 3 years ago