用于不可替代的令牌的标准接口，也称为行为。
以下标准允许在智能合约中实施NFT的标准API。该标准提供了跟踪和传输NFT的基本功能。
我们认为NFT的使用案例由个人拥有和交易，以及托运给第三方经纪人/钱包/拍卖商（“运营商”）。NFT可以代表对数字或实物资产的所有权。我们考虑了各种各样的资产，我们知道你会想到更多：
- 物理财产 - 房屋，独特的艺术品
- 虚拟收藏品 - 小猫，可收集卡片的独特图片
- “负值”资产 - 贷款，负担和其他责任
一般来说，所有房屋都是独特的，没有两只小猫是相同的。NFT是可区分的，您必须分别跟踪每个NFT 的所有权。
每个符合NRC-721标准的合同都必须实施NRC721和NRC165接口（以下“注意事项”）：
package io.nuls.token.interfaces;
import io.nuls.contract.sdk.Address;
import io.nuls.contract.sdk.Event;
import io.nuls.contract.sdk.annotation.View;
import java.math.BigInteger;
public interface INRC721 {
/**
* Count all NFTs assigned to an owner
* @param owner An address for whom to query the balance
* @return The number of NFTs owned by `owner`, possibly zero
*/
@View
int balanceOf(Address owner);
/**
* Find the owner of an NFT
* @param tokenId The identifier for an NFT
* @return The address of the owner of the NFT
*/
@View
Address ownerOf(BigInteger tokenId);
/**
* Transfers the ownership of an NFT from one address to another address.
* When transfer is complete, this function checks if `to` is a smart contract.
* If so, it calls `onNRC721Received` on `to` and throws if the return value is `false`.
* @throws revert unless `Msg.sender()` is the current owner, an authorized
* operator, or the approved address for this NFT.
* @throws revert if `from` is not the current owner.
* @throws revert if `tokenId` is not a valid NFT.
* @param from The current owner of the NFT
* @param to The new owner
* @param tokenId The NFT to transfer
* @param data Additional data with no specified format, sent in call to `to`
*/
void safeTransferFrom(Address from, Address to, BigInteger tokenId, String data);
/**
* Transfers the ownership of an NFT from one address to another address.
* This works identically to the other function with an extra data parameter,
* except this function just sets data to "".
* @param from The current owner of the NFT
* @param to The new owner
* @param tokenId The NFT to transfer
*/
void safeTransferFrom(Address from, Address to, BigInteger tokenId);
/**
* Transfer ownership of an NFT -- THE CALLER IS RESPONSIBLE
* TO CONFIRM THAT `to` IS CAPABLE OF RECEIVING NFTS OR ELSE
* THEY MAY BE PERMANENTLY LOST
* @throws Revert unless `Msg.sender()` is the current owner, an authorized
* operator, or the approved address for this NFT.
* @throws Revert if `from` is not the current owner.
* @throws Revert if `tokenId` is not a valid NFT.
* @param from The current owner of the NFT
* @param to The new owner
* @param tokenId The NFT to transfer
*/
void transferFrom(Address from, Address to, BigInteger tokenId);
/**
* Change or reaffirm the approved address for an NFT
* @throws revert unless `Msg.sender()` is the current NFT owner, or an authorized
* operator of the current owner.
* @param approved The new approved NFT controller
* @param tokenId The NFT to approve
*/
void approve(Address to, BigInteger tokenId);
/**
* Enable or disable approval for a third party ("operator") to manage
* all of `Msg.sender()`'s assets.
* Emits the ApprovalForAll event. The contract MUST allow multiple operators per owner.
* @param operator Address to add to the set of authorized operators
* @param approved True if the operator is approved, false to revoke approval
*/
void setApprovalForAll(Address operator, boolean approved);
/**
* Get the approved address for a single NFT.
* @throws revert if there is none or if `tokenId` is not a valid NFT.
* @param tokenId The NFT to find the approved address for
* @return The approved address for this NFT.
*/
Address getApproved(BigInteger tokenId);
/**
* Query if an address is an authorized operator for another address
* @param owner The address that owns the NFTs
* @param operator The address that acts on behalf of the owner
* @return True if `operator` is an approved operator for `owner`, false otherwise
*/
@View
boolean isApprovedForAll(Address owner, Address operator);
/**
* This emits when ownership of any NFT changes by any mechanism.
* This event emits when NFTs are created (`from` is NULL) and destroyed.
* At the time of any transfer, the approved address for that NFT (if any) is reset to none.
* <p>Exception: during contract creation, any number of NFTs may be created and assigned without emitting Transfer.</p>
*/
class Transfer implements Event {
private Address from;
private Address to;
private BigInteger tokenId;
public Transfer(Address from, Address to, BigInteger tokenId) {
this.from = from;
this.to = to;
this.tokenId = tokenId;
}
public Address getFrom() {
return from;
}
public void setFrom(Address from) {
this.from = from;
}
public Address getTo() {
return to;
}
public void setTo(Address to) {
this.to = to;
}
public BigInteger getTokenId() {
return tokenId;
}
public void setTokenId(BigInteger tokenId) {
this.tokenId = tokenId;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Transfer that = (Transfer) o;
if (from != null ? !from.equals(that.from) : that.from != null) return false;
if (to != null ? !to.equals(that.to) : that.to != null) return false;
return tokenId != null ? tokenId.equals(that.tokenId) : that.tokenId == null;
}
@Override
public int hashCode() {
int result = from != null ? from.hashCode() : 0;
result = 31 * result + (to != null ? to.hashCode() : 0);
result = 31 * result + (tokenId != null ? tokenId.hashCode() : 0);
return result;
}
@Override
public String toString() {
final StringBuilder sb = new StringBuilder("{");
sb.append("\"from\":")
.append('\"').append(from).append('\"');
sb.append(",\"to\":")
.append('\"').append(to).append('\"');
sb.append(",\"tokenId\":")
.append('\"').append(tokenId).append('\"');
sb.append('}');
return sb.toString();
}
}
/**
* This emits when the approved address for an NFT is changed or reaffirmed.
* When a Transfer event emits, this also indicates that the approved address for that NFT (if any) is reset to none.
*/
class Approval implements Event {
private Address owner;
private Address approved;
private BigInteger tokenId;
public Approval(Address owner, Address approved, BigInteger tokenId) {
this.owner = owner;
this.approved = approved;
this.tokenId = tokenId;
}
public Address getOwner() {
return owner;
}
public void setOwner(Address owner) {
this.owner = owner;
}
public Address getApproved() {
return approved;
}
public void setApproved(Address approved) {
this.approved = approved;
}
public BigInteger getTokenId() {
return tokenId;
}
public void setTokenId(BigInteger tokenId) {
this.tokenId = tokenId;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Approval approval = (Approval) o;
if (owner != null ? !owner.equals(approval.owner) : approval.owner != null) return false;
if (approved != null ? !approved.equals(approval.approved) : approval.approved != null) return false;
if (tokenId != null ? !tokenId.equals(approval.tokenId) : approval.tokenId != null) return false;
return true;
}
@Override
public int hashCode() {
int result = owner != null ? owner.hashCode() : 0;
result = 31 * result + (approved != null ? approved.hashCode() : 0);
result = 31 * result + (tokenId != null ? tokenId.hashCode() : 0);
return result;
}
@Override
public String toString() {
final StringBuilder sb = new StringBuilder("{");
sb.append("\"owner\":")
.append('\"').append(owner).append('\"');
sb.append(",\"approved\":")
.append('\"').append(approved).append('\"');
sb.append(",\"tokenId\":")
.append('\"').append(tokenId).append('\"');
sb.append('}');
return sb.toString();
}
}
/**
* This emits when an operator is enabled or disabled for an owner.
* The operator can manage all NFTs of the owner.
*/
class ApprovalForAll implements Event {
private Address owner;
private Address operator;
private Boolean approved;
public ApprovalForAll(Address owner, Address operator, Boolean approved) {
this.owner = owner;
this.operator = operator;
this.approved = approved;
}
public Address getOwner() {
return owner;
}
public void setOwner(Address owner) {
this.owner = owner;
}
public Address getOperator() {
return operator;
}
public void setOperator(Address operator) {
this.operator = operator;
}
public Boolean getApproved() {
return approved;
}
public void setApproved(Boolean approved) {
this.approved = approved;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
ApprovalForAll that = (ApprovalForAll) o;
if (owner != null ? !owner.equals(that.owner) : that.owner != null) return false;
if (operator != null ? !operator.equals(that.operator) : that.operator != null) return false;
if (approved != null ? !approved.equals(that.approved) : that.approved != null) return false;
return true;
}
@Override
public int hashCode() {
int result = owner != null ? owner.hashCode() : 0;
result = 31 * result + (operator != null ? operator.hashCode() : 0);
result = 31 * result + (approved != null ? approved.hashCode() : 0);
return result;
}
@Override
public String toString() {
final StringBuilder sb = new StringBuilder("{");
sb.append("\"owner\":")
.append('\"').append(owner).append('\"');
sb.append(",\"operator\":")
.append('\"').append(operator).append('\"');
sb.append(",\"approved\":")
.append(approved);
sb.append('}');
return sb.toString();
}
}
}package io.nuls.token.interfaces;
public interface INRC165 {
/**
* Query if a contract implements an interface
* @param interfaceName The interface name, as specified in the implementation class of NRC-165.
* eg. interfaceName: ['INRC165', 'INRC721', 'INRC721Enumerable', 'INRC721Metadata']
* @return `true` if the contract implements `interfaceName`, `false` otherwise
*/
boolean supportsInterface(String interfaceName);
}钱包/经纪/拍卖应用程序必须实现钱包接口， 如果它将接受安全转移。
package io.nuls.token.interfaces;
import io.nuls.contract.sdk.Address;
import java.math.BigInteger;
public interface INRC721TokenReceiver {
/**
* Handle the receipt of an NFT.
* The NRC721 smart contract calls this function on the recipient
* after a `transfer`. This function MAY revert and reject the
* transfer.
* Note: the contract address is always the message sender.
* @param operator The address which called `safeTransferFrom` function
* @param from The address which previously owned the token
* @param tokenId The NFT identifier which is being transferred
* @param data Additional data with no specified format
* @return `true` if it accepts NFTs from other contracts, otherwise `false`
*/
boolean onNRC721Received(Address operator, Address from, BigInteger tokenId, String data);
}对于NRC-721智能合约，元数据扩展是可选的（参见下面的“警告”）。这样可以查询您的智能合约的名称以及您的NFT所代表的资产的详细信息。
package io.nuls.token.interfaces;
import io.nuls.contract.sdk.annotation.View;
import java.math.BigInteger;
public interface INRC721Metadata {
/**
* @return A descriptive name for a collection of NFTs in this contract
*/
@View
String name() ;
/**
* @return An abbreviated name for NFTs in this contract
*/
@View
String symbol() ;
/**
* @return A distinct Uniform Resource Identifier (URI) for a given asset.
* NULL if `tokenId` is not a valid NFT.
*/
@View
String tokenURI(BigInteger tokenId) ;
}对于NRC-721智能合约，枚举扩展是可选的（参见下面的“警告”）。这允许您的合同发布其完整的NFT列表并使其可被发现。
package io.nuls.token.interfaces;
import io.nuls.contract.sdk.Address;
import io.nuls.contract.sdk.annotation.View;
import java.math.BigInteger;
public interface INRC721Enumerable {
/**
* Count NFTs tracked by this contract
* @return A count of valid NFTs tracked by this contract, where each one of
* them has an assigned and queryable owner
*/
@View
int totalSupply();
/**
* Enumerate valid NFTs
* @param index A counter less than `totalSupply()`
* @return The token identifier for the `index` NFT,
* (sort order not specified), NULL if `index` >= `totalSupply()`.
*/
@View
BigInteger tokenByIndex(int index);
/**
* Enumerate NFTs assigned to an owner
* @param owner An address where we are interested in NFTs owned by them
* @param index A counter less than `balanceOf(_owner)`
* @return The token identifier for the `index` NFT assigned to `owner`,
* (sort order not specified), NULL if `index` >= `balanceOf(owner)` or invalid NFTs.
*/
@View
BigInteger tokenOfOwnerByIndex(Address owner, int index);
}此智能合约的许多建议用途依赖于跟踪可区分的资产。现有或计划的NFT的示例是Decentraland中的LAND，CryptoPunks中的同名朋友，以及使用DMarket或EnjinCoin等系统的游戏内物品。未来的用途包括跟踪现实世界的资产，如房地产（如Ubitquity或Propy等公司所设想的那样。在这些情况中，这些项目在分类账中不是“集中在一起”，而是每个资产，这一点至关重要。必须拥有单独和原子跟踪的所有权。无论这些资产的性质如何，如果我们拥有允许跨功能资产管理和销售平台的标准化界面，生态系统将更加强大。
NFT标识符
每个NFT都由BigIntegerNRC-721智能合约中的唯一ID标识。该识别号码在合同期限内不得更改。该对(Address contractAddress, BigInteger tokenId)然后将用于在链上特定资产的全局唯一和完全合格的标识符。虽然一些NRC-721智能合约可能会发现从ID 0开始并且每个新NFT只增加一个是方便的，但是呼叫者不应该假设ID号具有任何特定模式，并且必须将ID视为“黑匣子” ”。另请注意，NFT可能无效（被销毁）。请参阅支持的枚举接口的枚举函数。
转移机制
NRC-721标准化了安全传递函数safeTransferFrom（带有和不带String参数的重载方法）和不安全的功能transferFrom。转移可以通过以下方式启动：
- NFT的所有者
- NFT当前经批准的地址
- NFT当前所有者的授权操作者
另外，授权操作者可以设置NFT的批准地址。这为钱包，经纪人和拍卖应用程序提供了一套强大的工具，可以快速使用大量的NFT。
创建NFT（“铸造”）和销毁NFT（“燃烧”）不包括在规范中。您的合同可以通过其他方式实现。
NRC-165接口
我们选择标准接口检测（NRC-165）来公开NRC-721智能合约支持的接口。
气体和复杂性（关于枚举扩展）
该规范设想了管理少量和任意大量 NFT的实现。如果您的应用程序能够增长，那么请避免在代码中使用for / while循环。这些表明您的合同可能无法扩展，燃气成本将随着时间的推移不断增加。
隐私
在激励部分中确定的钱包/经纪人/拍卖者非常需要确定所有者拥有哪些NFT。
考虑一个NFT不可枚举的用例可能很有意思，例如财产所有权的私人注册表或部分私有注册表。但是，无法获得隐私，因为攻击者可以为所有可能的tokenId简单地调用ownerOf。
元数据选择（元数据扩展）
我们在元数据扩展中需要name和symbol功能。
我们提醒实现作者，空字符串是一个有效的响应name，symbol，如果你抗议使用这种机制。我们也提醒大家，任何智能合同可以使用相同的名称和符号作为你的合同。客户如何确定哪些NRC-721智能合约是众所周知的（规范的）超出了本标准的范围。
提供了一种将NFT与URI相关联的机制。我们希望许多实现将利用此功能为每个NFT提供元数据，URI可能是可变的（即它会不时变化）。我们考虑了代表房屋所有权的NFT，在这种情况下，关于房屋的元数据（图像，居住者等）可以自然地改变。
元数据作为字符串值返回。
考虑的替代方案：将每个资产的所有元数据放在区块链上（太贵），使用URL模板查询元数据部分
- 最基本实现 https://github.com/MIMIEYES/NULS-NRC721-baselib
- NRC721Metadata基本功能实现 https://github.com/MIMIEYES/NRC721Metadata
- NRC721Enumerable基本功能实现 https://github.com/MIMIEYES/NRC721Enumerable
- NRC721Full基本功能实现 https://github.com/MIMIEYES/NRC721Full
- NRC721Receiver基本功能实现 https://github.com/MIMIEYES/NRC721Receiver