智能合約在區(qū)塊鏈上的可執(zhí)行代碼是一種類似匯編語言的指令集，這些指令集通過EVM的解釋和執(zhí)行，對區(qū)塊鏈的狀態(tài)進行讀寫，實現(xiàn)合約規(guī)定的業(yè)務(wù)邏輯。Therefore,through Solidity,a high-level programming language,and Solidity compiler,you can compile High-level programming language into assembly instruction set code,and then deploy it to the blockchain for execution.

　　一套完整的區(qū)塊鏈DAPP，除智能合約這些可以查詢和改變區(qū)塊鏈狀態(tài)的代碼外，還需要用戶操作界面及連接用戶操作與智能合約代碼的接口。

　　pragma solidity^0.8.0;

　　import"../IERC721.sol";

　　/**

　　*title ERC-721 Non-Fungible Token Standard,optional enumeration extension

　　*dev See https://eips.ethereum.org/EIPS/eip-721

　　*/

　　interface IERC721Enumerable is IERC721{

　　/**

　　*dev Returns the total amount of tokens stored by the contract.

　　*返回NFT總量

　　*/

　　function totalSupply()external view returns(uint256);

　　/**

　　*dev Returns a token ID owned by`owner`at a given`index`of its token list.

　　*Use along with{balanceOf}to enumerate all of``owner``'s tokens.

　　*所有者可以一次擁有多個的NFT,此函數(shù)返回_owner擁有的NFT列表中對應(yīng)索引的tokenId

　　*/

　　function tokenOfOwnerByIndex(address owner,uint256 index)external view returns(uint256 tokenId);

　　/**

　　*dev Returns a token ID at a given`index`of all the tokens stored by the contract.

　　*Use along with{totalSupply}to enumerate all tokens.

　　*通過索引返回對應(yīng)的tokenId

　　*/

　　function tokenByIndex(uint256 index)external view returns(uint256);

　　}