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03-erc721-3.md

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title actions requireLogin material
balanceOf 和 ownerOf
checkAnswer
hints
true
editor
language startingCode answer
sol
zombieownership.sol zombieattack.sol zombiehelper.sol zombiefeeding.sol zombiefactory.sol ownable.sol erc721.sol
pragma solidity ^0.4.19; import "./zombieattack.sol"; import "./erc721.sol"; contract ZombieOwnership is ZombieAttack, ERC721 { function balanceOf(address _owner) public view returns (uint256 _balance) { // 1. 在这里返回 `_owner` 拥有的僵尸数 } function ownerOf(uint256 _tokenId) public view returns (address _owner) { // 2. 在这里返回 `_tokenId` 的所有者 } function transfer(address _to, uint256 _tokenId) public { } function approve(address _to, uint256 _tokenId) public { } function takeOwnership(uint256 _tokenId) public { } }
pragma solidity ^0.4.19; import "./zombiehelper.sol"; contract ZombieBattle is ZombieHelper { uint randNonce = 0; uint attackVictoryProbability = 70; function randMod(uint _modulus) internal returns(uint) { randNonce++; return uint(keccak256(now, msg.sender, randNonce)) % _modulus; } function attack(uint _zombieId, uint _targetId) external ownerOf(_zombieId) { Zombie storage myZombie = zombies[_zombieId]; Zombie storage enemyZombie = zombies[_targetId]; uint rand = randMod(100); if (rand <= attackVictoryProbability) { myZombie.winCount++; myZombie.level++; enemyZombie.lossCount++; feedAndMultiply(_zombieId, enemyZombie.dna, "zombie"); } else { myZombie.lossCount++; enemyZombie.winCount++; _triggerCooldown(myZombie); } } }
pragma solidity ^0.4.19; import "./zombiefeeding.sol"; contract ZombieHelper is ZombieFeeding { uint levelUpFee = 0.001 ether; modifier aboveLevel(uint _level, uint _zombieId) { require(zombies[_zombieId].level >= _level); _; } function withdraw() external onlyOwner { owner.transfer(this.balance); } function setLevelUpFee(uint _fee) external onlyOwner { levelUpFee = _fee; } function levelUp(uint _zombieId) external payable { require(msg.value == levelUpFee); zombies[_zombieId].level++; } function changeName(uint _zombieId, string _newName) external aboveLevel(2, _zombieId) ownerOf(_zombieId) { zombies[_zombieId].name = _newName; } function changeDna(uint _zombieId, uint _newDna) external aboveLevel(20, _zombieId) ownerOf(_zombieId) { zombies[_zombieId].dna = _newDna; } function getZombiesByOwner(address _owner) external view returns(uint[]) { uint[] memory result = new uint[](ownerZombieCount[_owner]); uint counter = 0; for (uint i = 0; i < zombies.length; i++) { if (zombieToOwner[i] == _owner) { result[counter] = i; counter++; } } return result; } }
pragma solidity ^0.4.19; import "./zombiefactory.sol"; contract KittyInterface { function getKitty(uint256 _id) external view returns ( bool isGestating, bool isReady, uint256 cooldownIndex, uint256 nextActionAt, uint256 siringWithId, uint256 birthTime, uint256 matronId, uint256 sireId, uint256 generation, uint256 genes ); } contract ZombieFeeding is ZombieFactory { KittyInterface kittyContract; modifier ownerOf(uint _zombieId) { require(msg.sender == zombieToOwner[_zombieId]); _; } function setKittyContractAddress(address _address) external onlyOwner { kittyContract = KittyInterface(_address); } function _triggerCooldown(Zombie storage _zombie) internal { _zombie.readyTime = uint32(now + cooldownTime); } function _isReady(Zombie storage _zombie) internal view returns (bool) { return (_zombie.readyTime <= now); } function feedAndMultiply(uint _zombieId, uint _targetDna, string _species) internal ownerOf(_zombieId) { Zombie storage myZombie = zombies[_zombieId]; require(_isReady(myZombie)); _targetDna = _targetDna % dnaModulus; uint newDna = (myZombie.dna + _targetDna) / 2; if (keccak256(_species) == keccak256("kitty")) { newDna = newDna - newDna % 100 + 99; } _createZombie("NoName", newDna); _triggerCooldown(myZombie); } function feedOnKitty(uint _zombieId, uint _kittyId) public { uint kittyDna; (,,,,,,,,,kittyDna) = kittyContract.getKitty(_kittyId); feedAndMultiply(_zombieId, kittyDna, "kitty"); } }
pragma solidity ^0.4.19; import "./ownable.sol"; contract ZombieFactory is Ownable { event NewZombie(uint zombieId, string name, uint dna); uint dnaDigits = 16; uint dnaModulus = 10 ** dnaDigits; uint cooldownTime = 1 days; struct Zombie { string name; uint dna; uint32 level; uint32 readyTime; uint16 winCount; uint16 lossCount; } Zombie[] public zombies; mapping (uint => address) public zombieToOwner; mapping (address => uint) ownerZombieCount; function _createZombie(string _name, uint _dna) internal { uint id = zombies.push(Zombie(_name, _dna, 1, uint32(now + cooldownTime), 0, 0)) - 1; zombieToOwner[id] = msg.sender; ownerZombieCount[msg.sender]++; NewZombie(id, _name, _dna); } function _generateRandomDna(string _str) private view returns (uint) { uint rand = uint(keccak256(_str)); return rand % dnaModulus; } function createRandomZombie(string _name) public { require(ownerZombieCount[msg.sender] == 0); uint randDna = _generateRandomDna(_name); randDna = randDna - randDna % 100; _createZombie(_name, randDna); } }
pragma solidity ^0.4.19; /** * @title Ownable * @dev The Ownable contract has an owner address, and provides basic authorization control * functions, this simplifies the implementation of "user permissions". */ contract Ownable { address public owner; event OwnershipTransferred(address indexed previousOwner, address indexed newOwner); /** * @dev The Ownable constructor sets the original `owner` of the contract to the sender * account. */ function Ownable() public { owner = msg.sender; } /** * @dev Throws if called by any account other than the owner. */ modifier onlyOwner() { require(msg.sender == owner); _; } /** * @dev Allows the current owner to transfer control of the contract to a newOwner. * @param newOwner The address to transfer ownership to. */ function transferOwnership(address newOwner) public onlyOwner { require(newOwner != address(0)); OwnershipTransferred(owner, newOwner); owner = newOwner; } }
contract ERC721 { event Transfer(address indexed _from, address indexed _to, uint256 _tokenId); event Approval(address indexed _owner, address indexed _approved, uint256 _tokenId); function balanceOf(address _owner) public view returns (uint256 _balance); function ownerOf(uint256 _tokenId) public view returns (address _owner); function transfer(address _to, uint256 _tokenId) public; function approve(address _to, uint256 _tokenId) public; function takeOwnership(uint256 _tokenId) public; }
pragma solidity ^0.4.19; import "./zombieattack.sol"; import "./erc721.sol"; contract ZombieOwnership is ZombieAttack, ERC721 { function balanceOf(address _owner) public view returns (uint256 _balance) { return ownerZombieCount[_owner]; } function ownerOf(uint256 _tokenId) public view returns (address _owner) { return zombieToOwner[_tokenId]; } function transfer(address _to, uint256 _tokenId) public { } function approve(address _to, uint256 _tokenId) public { } function takeOwnership(uint256 _tokenId) public { } }

太棒了,我们来深入讨论一下 ERC721 的实现。

我们已经把所有你需要在本课中实现的函数的空壳复制好了。

在本章节,我们将实现头两个方法: balanceOfownerOf

balanceOf

  function balanceOf(address _owner) public view returns (uint256 _balance);

这个函数只需要一个传入 address 参数,然后返回这个 address 拥有多少代币。

在我们的例子中,我们的“代币”是僵尸。你还记得在我们 DApp 的哪里存储了一个主人拥有多少只僵尸吗?

ownerOf

  function ownerOf(uint256 _tokenId) public view returns (address _owner);

这个函数需要传入一个代币 ID 作为参数 (我们的情况就是一个僵尸 ID),然后返回该代币拥有者的 address

同样的,因为在我们的 DApp 里已经有一个 mapping (映射) 存储了这个信息,所以对我们来说这个实现非常直接清晰。我们可以只用一行 return 语句来实现这个函数。

注意:要记得, uint256 等同于uint。我们从课程的开始一直在代码中使用 uint,但从现在开始我们将在这里用 uint256,因为我们直接从规范中复制粘贴。

实战演习

我将让你来决定如何实现这两个函数。

每个函数的代码都应该只有1行 return 语句。看看我们在之前课程中写的代码,想想我们都把这个数据存储在哪。如果你觉得有困难,你可以点“我要看答案”的按钮来获得帮助。

  1. 实现 balanceOf 来返回 _owner 拥有的僵尸数量。

  2. 实现 ownerOf 来返回拥有 ID 为 _tokenId 僵尸的所有者的地址。