1.首先我们在bsc testnet 和 rinkeby 上各发一份erc721合约 开放mint权限 实现一个nft跨链

    function mint(uint256 tokenId,address receiver) external  whenNotPaused  {
        require(!_exists(tokenId), 'Token does  exist');
        _safeMint(receiver, tokenId );
    }

分别以 bsc_nft,rinkeby_nft 表示

2.分别在bsc_testnet 与 rinkeby 链上分别部署一份跨链合约
RinkebyToBsc

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.6;

import "./NonblockingReceiver.sol";

interface Nft {

    
    function mint(uint256 tokenId,address receiver) external;
    function burn(uint256 tokenId) external;
}
// chainId: 10001
// endpoint: 0x79a63d6d8BBD5c6dfc774dA79bCcD948EAcb53FA
// nft 0x72a8d73C145b4Aeb1D89530049edc2e66D34CeE3
// 
contract RinkebyToBsc is NonblockingReceiver {

    uint gasForDestinationLzReceive = 350000;

    address public _nft;

    uint16 public _chainId;

    constructor(uint16 chainId, address nft,address _layerZeroEndpoint){ 
       
        endpoint = ILayerZeroEndpoint(_layerZeroEndpoint);
        _nft = nft;
        _chainId = chainId;
    }

    function _LzReceive(uint16 _srcChainId, bytes memory _srcAddress, uint64 _nonce, bytes memory _payload) override internal {
        _srcChainId;
        _nonce;
        _srcAddress;
        // decode
        (address toAddr, uint tokenId) = abi.decode(_payload, (address, uint));
         Nft(_nft).mint(tokenId,toAddr);
    } 

    function crossChain(uint256 tokenId) public payable {
        //require(msg.sender == ownerOf(tokenId), "You must own the token to traverse");
        require(trustedRemoteLookup[_chainId].length > 0, "This chain is currently unavailable for travel");
         Nft(_nft).burn(tokenId);
         bytes memory payload = abi.encode(msg.sender, tokenId);

         uint16 version = 1;
        bytes memory adapterParams = abi.encodePacked(version, gasForDestinationLzReceive);

        // get the fees we need to pay to LayerZero + Relayer to cover message delivery
        // you will be refunded for extra gas paid
        (uint messageFee, ) = endpoint.estimateFees(_chainId, address(this), payload, false, adapterParams);
        
        require(msg.value >= messageFee, "GG: msg.value not enough to cover messageFee. Send gas for message fees");

        endpoint.send{value: msg.value}(
            _chainId,                           // destination chainId
            trustedRemoteLookup[_chainId],      // destination address of nft contract
            payload,                            // abi.encoded()'ed bytes
            payable(msg.sender),                // refund address
            address(0x0),                       // 'zroPaymentAddress' unused for this
            adapterParams                       // txParameters 
        );
        
    } 
}

BscToRinkey

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.6;

import "./NonblockingReceiver.sol";

interface Nft {

    
    function mint(uint256 tokenId,address receiver) external;
    function burn(uint256 tokenId) external;
}

// chainId: 10002
// endpoint: 0x6Fcb97553D41516Cb228ac03FdC8B9a0a9df04A1
// nft 0x0cE833406B536588eaB8cd6fA1be26Ef2FE43B8c
//0xC4AfE6Df930EF422f00A4270419Ce65FBeB9C640
contract BscToRinkey is NonblockingReceiver {

    uint gasForDestinationLzReceive = 350000;

    address public _nft;

    uint16 public _chainId;

    constructor(uint16 chainId, address nft,address _layerZeroEndpoint){  //在构造方法中 初始化号一些基本参数 内容可以在这里找到 https://layerzero.gitbook.io/docs/technical-reference/testnet/testnet-addresses
       
        endpoint = ILayerZeroEndpoint(_layerZeroEndpoint); 
        _nft = nft;
        _chainId = chainId;
    }

    function _LzReceive(uint16 _srcChainId, bytes memory _srcAddress, uint64 _nonce, bytes memory _payload) override internal { //接收到跨链请求后需要的操作  也就是给用户在当前链mint的一个当前链的nft ，这个函数由ILayerZeroEndpoint 调用传递跨链_payload到目标链
        _srcChainId;
        _nonce;
        _srcAddress;
        // decode
        (address toAddr, uint tokenId) = abi.decode(_payload, (address, uint));
         Nft(_nft).mint(tokenId,toAddr);
    } 
 
    function crossChain(uint256 tokenId) public payable {                                        //跨链 
        //require(msg.sender == ownerOf(tokenId), "You must own the token to traverse");
        require(trustedRemoteLookup[_chainId].length > 0, "This chain is currently unavailable for travel");
         Nft(_nft).burn(tokenId);
         bytes memory payload = abi.encode(msg.sender, tokenId);  // encode 参数

         uint16 version = 1;
        bytes memory adapterParams = abi.encodePacked(version, gasForDestinationLzReceive);

        // get the fees we need to pay to LayerZero + Relayer to cover message delivery
        // you will be refunded for extra gas paid
        (uint messageFee, ) = endpoint.estimateFees(_chainId, address(this), payload, false, adapterParams);
        
        require(msg.value >= messageFee, "GG: msg.value not enough to cover messageFee. Send gas for message fees"); //跨链费

        endpoint.send{value: msg.value}(      //ILayerZeroEndpoint  跨链并带上参数
            _chainId,                           // destination chainId
            trustedRemoteLookup[_chainId],      // destination address of nft contract  //你需要让layerzero跨链后传递消息的目标地址，这个是手动set进去的 以chainId为key的mapping  其实就是我们部署的RinkebyToBsc 地址；
            payload,                            // abi.encoded()'ed bytes
            payable(msg.sender),                // refund address
            address(0x0),                       // 'zroPaymentAddress' unused for this
            adapterParams                       // txParameters 
        ); 
        
    } 
}

调用

function setTrustedRemote(uint16 _chainId, bytes calldata _trustedRemote) external  {
        trustedRemoteLookup[_chainId] = _trustedRemote;
    }

set 目标链的目标地址
合约涉及的其他合约可以在官方文档找到 https://layerzero.gitbook.io/docs/guides/interfaces/evm-solidity-interfaces

整个过程还是比较简单 首先layerzero在各个链都有部署了endpoint，endpoint定义的跨链的参数等等， 在执行跨链时 endpoint 会调用当前链的轻节点合约会通知chainLink，和 relayer。chainLink去链下拿到交易在当前链发生的最终证明好像是一个区块的receipthash，relayer 去准备这笔交易的proof ，分别提交到目标链 。目标链的轻节点合约拿到chainLink与relayer 的东西来验证跨链交易 验证通过后 调用 endpoint去调用目标合约的LzReceive 方法 完成跨链。