Questions tagged [erc-721]

Relating to ERC-721, the standard for Non-Fungible Tokens (also known as Deeds)

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When extending a contract how to call the external constructor and pass parameters?

I have the following contract import "zeppelin-solidity/contracts/token/ERC721/ERC721Token.sol"; contract Contract is ERC721Token { function Contract(string _name, string _symbol) public { ...
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erc-721 erc-20 solidity code check effects interaction pattern

Where can one locate a formally verified ERC20/ERC721 solidity code/template that adheres to security design patterns such as check effects interaction patterns?
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Use of the “indexed” keyword and token standards

Long story short, while making a blockchain crawler that would extract all ERC20 transactions I learned the hard way that ERC721 has the same "signature" as ERC20 (and probably many others that I ...
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How are ERC-721 protocol tokens different from Ardor assets? Is there a pro/con data sheet?

ERC-721 protocol is used to create unique tokens like crypto kitties, but I'm curious has anyone compared it to the Ardor Ignis singleton assets as it seems like it does something similar. Is there a ...
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694 views

Transfer an ERC721 Token from another contract

I'm getting a revert when trying to transfer a token from another contract, I'm calling the function from an Auctions contract, for example, when the max bidder claims the reward they get the token ...
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Truffle test failing due to different data type than expected

I am using truffle and ganache to make a token demo for myself. I'm following this guide then making my own changes according to my project. When I try running tests to verify that my contract is ...
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685 views

List ERC721 tokens owned by a user on a web page

Let's say that I have an ERC721 (NFT) contract that represents a set of playing cards. Is there sample code out there that shows listing all of the tokens of that ERC721 contract that a user owns on ...
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1answer
48 views

Does ERC-20 or ERC-721 compliance mean anything of consequence? Are these standards necessary to use

Why do we have to use these standards? Is complying with these standards a necessity if we want our token to be listed anywhere? If our token doesn't fit within the listed standard, can we still have ...
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Can hd wallets have different withdrawal permission levels?

Specifically, is it possible for a wallet to have a key which can spend an ERC721 collectible, but its child keys not?
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1answer
238 views

Calling function from another contract reverts

I've been developing a dApp that needs ERC721 tokens. I have three contracts, a base contract, the one to mint tokens and another one for auctions. The inheritance looks like Base > Token > Auctions. ...
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Tokens standards on go-ethereum and Quorum - ERC721

Someone just told me that Quorum does not implement EIP721, so it does not support ERC721 tokens. I always though token standards are just standards you should follow in your smart contract code and ...
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523 views

Calling a function inheriting onlyOwner via other contract

I need to call mint() function in MyNFToken.sol via MyContract.sol. Ownable.sol pragma solidity ^0.4.20; contract Ownable { address public owner; function Ownable() public { owner = msg.sender;...
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260 views

ERC 721 rental contract

I am trying to write a contract for renting cars . I have implemented the following addCar -> to add a new car to the lot rentCar -> trasfers te ownership of the car to the rentee,and creates a rent ...
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365 views

Adding metadata to ERC721 tokens

could the metadata inn ERC721 be altered after issuing a token ? I want to create an contract allowing people changing the Token metadata content (on the tokens purchased in ICO).
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What Are Good Specific Reasons The onERC721Received Function Returns A Magic Value?

The ERC721 standard says the following: The onERC721Received function specifically works around old deployed contracts which may inadvertently return 1 (true) in certain circumstances even if they ...
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269 views

Can ERC-721 accept ERC-20 Tokens as a payment method

I am using OpenZeppelin as my open sourced framework for my blockchain development. I am interested to see if there is a work around to accept ERC-20 tokens as payment for the ERC-721 token? Example:...
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200 views

cross-chain atomic swaps for ERC721

Can cross-chain atomic swaps be implemented for ERC721 too? What are some limitations, if any?
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284 views

Does each ERC-721 token have its own address?

I'm trying to create NFTs (non-fungible tokens), but I don't quite understand this part - is each token its own contract? or are all of them stored in the NFT equivalent of a 'balances' mapping in a ...
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1answer
148 views

Execution of ERC721 Token

I have a Node-js application where cards are generated with unique number (ID11234). So I am planning to map a token for each card. In order to get uniqueness, I went through some of the documents, at-...
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Hardware wallet support of ERC-721 or Storing cryptokitties on Ledger Nano

I have a question related to hardware wallet support of ERC 721 tokens. I plan to move a cryptokittie to a Ledger Nano wallet. It's relatively easy to send it to an account controlled by Ledger. In ...
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What are the main design pattern examples for using Callbacks in Smart Contracts?

In the ERC721 standard, there is a Wallet interface standard called ERC721TokenReceiver which includes a function called onERC721Received. I believe this is so that Wallets can listen to events and ...
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1answer
72 views

Creating a token order book without costing gas

I'm building a DApp for ERC721 collectibles. I want to make it more like rarepepewallet.com than CryptoKitties: RarePepeWallet has an order book for each token, matching asks with bids, just like any ...
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319 views

erc721 token uniqueness

I am doing research on using the erc721 interface to represent a digital good on an exchange. For simplicity's sake, let's say that these goods are a digital representation of a collectible card game (...
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526 views

ERC721 Scalability

I've just implemented several SCs in order to accomplish the ERC721 functionality but I'm facing a critical issue related to the scalability when I want to create a great number of tokens. I'm storing ...
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1answer
176 views

How do OpenZeppelin ERC721 tests pass?

I don't understand how the following test can pass. I tried it in my application and it fails. The entry point is the description 'when called by the owner'. In this function two test cases are ...
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521 views

ERC721 Token unique string

I am trying to understand how to use the ERC721 token.I want to change the function mint with parameter of type uint256 to parameter of type string and create a unique string, it's possible to replace ...
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1answer
318 views

How to get value history from ERC721 Token

I'm trying to figure out HOW to get a sort of "history" of values for a specific ERC721 (for instance KnownOrigin) What are the important items to consider? Is something feasible via Smart Contract ...
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Does an ERC721 contract have to rely on an external agent to be the approved spender?

I am creating a dApp that services a game. The "house" in the game is my game server that creates the smart contract using Web3.js. It also owns all the non-fungible assets at the start of the game, ...
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1answer
624 views

What's the point of ERC721Receiver.sol and ERC721Holder.sol in OpenZeppelin's implementation?

I'm studying OpenZeppelin's ERC721 token implementation and I'm having a hard time making sense of ERC721Receiver.sol and ERC721Holder.sol and how they relate to eachother. In the file ...
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What is the difference between an approved address and an operator address?

I'm looking at OpenZeppelin's implementation of an ERC721 token and I'm lost at what the difference is between an approved address and an operator address. Here's a code snippet: /// @dev Checks msg....
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ERC20 Interfaces overwriting ERC721 functions - Possible to adhere to standard?

Is it possible to have a contract that both generates and manages its own NFT according to the ERC721 Standard, and is able to make calls to outside ERC20 contracts? My contract currently inherits the ...
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81 views

Extend ERC721 without breaking standard

I want to make some extension to the ERC721. Per example, set some tokens as "requestable" (anyone can request it), if the requester know the "key" of each token So, I added a mapping with string ...
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Can't wrap my head around a mapping of mappings

I'm trying to fully comprehend what is going on in a standard ERC721 token. But this statement is really tripping me up: // Mapping from owner to operator approvals mapping (address => mapping (...
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659 views

How can I use ERC20 tokens in a way to buy an ERC721 token?

I would like to do a smart contract that allow me to buy an ERC721 token using an ERC20 token to pay In my mind is something like: -I create a ERC721 token -I create a ERC20 token -I have a ...
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Correct Open Zeppelin contract for external agent contract that handles sales logic on behalf of an ERC721 contract?

I just finished this article on the Open Zeppelin ERC721 token implementation: https://medium.com/blockchannel/walking-through-the-erc721-full-implementation-72ad72735f3c I about to start ...
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2k views

How to get metadata from ERC721

I'm trying to get Metadata from ERC721 token. Actually I'm trying to do it via ETHERSCAN and blockcypher APIs but I can't find the metadata in the response (like the Picture URL or the IPFS ID) Can ...
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447 views

How to display a list of ERC721 items starting from a pubblic address

I'd like to understand more about this ERC721 non-fungible tokens. I bought some cryptokitties (non 721), some art on KnownOrigin and now I want to display them in a web page. For Cryptokitties I'm ...
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Error encountered bailing. network state unknown. TypeError: contract.detectNetwork is no a fnction

I used "Zeppelin-solidity" to publish the ERC 721 token and compiled the sample code with truffle. However When migrating with "truffle", the following error occurs. Why? Error encountered, ...
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810 views

Inheritance of constructor [duplicate]

Why does warning appear with inheritance of constructor? contract MyToken is ERC721Token{ function MyToken(string _name, string _symbol) ERC721Token(_name, _symbol) public { } The content of the ...
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Is it possible to make a token that is unique to a pair of addresses?

As we know, each ERC721 token is unique in the sense that each of them is assigned to an address. I wonder if it is possible to go further and make tokens that is unique to a pair of addresses? i.e. ...
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How exactly is ERC721 tokens non-fungible?

What makes them unique as compared to the ERC20? Is it the owner's address as included in the form of token id? So what makes them unique is the historical chain of addresses attached to it?
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Can erc721 belong to another erc721 token?

I learnt somewhere today that an erc721 token doesn't have to belong to an account, it could belong to another erc721! How can this be implemented? where can I read more of this? Thanks
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291 views

Tracking transfers of ERC-721 tokens from another contract

I have an ERC-721 token manager contract and an ERC-721 token contract. The manager contract is responsible for creating new ERC-721 contracts and minting new tokens within those contracts, as well as ...
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149 views

Extending ERC-721 with additional functionality

I am building a DAPP using ERC-721 tokens. I have some additional functionality I am layering on the ERC-721 contract while keeping all the required interfaces intact. Will it still be an ERC-721 ...
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1answer
95 views

ERC721 “Digibles”: different than Bitcoin colored coin concept?

As I understand ERC721 contracts, in particular Cryptokitties, a cryptokitty is not associated with a piece of ETH but rather is just some storage associated with the Cryptokitty smart contract. Is ...
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953 views

ERC-165 query on ERC-721 implementation

While testing ERC-721 implementation from https://github.com/m0t0k1ch1/ERC721-token-sample/blob/master/contracts/MyNonFungibleToken.sol and trying to query the method supportsInterface I got the ...
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Why does an ERC721 contract need to conform to the ERC721 and ERC165 standard?

Reading through the EIP for ERC 721 I notice that it is required to implement 2 different interfaces. Why is this? I noticed this portion in the documentation, but I think some clarification is ...
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165 views

What happens when two people call a transfer function at the same time?

I am doing a decentralized market of tokens ERC 721 and I have the problem that if two people give to buy the token at the same time, I do not know what would happen. Is there any way, without ...
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Most efficient way of generating random ERC 721 NFT

I'm just getting into Solidity by building a first project around collectibles, ERC 721. There's for example 1500 different collectibles, each has an available amount defined by a criteria. These ...
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ERC-721 safeTransferFrom is overloaded?

According to ERC-721 interface the function safeTransferFrom seems to be overloaded: function safeTransferFrom(address _from, address _to, uint256 _tokenId) public; function safeTransferFrom(address ...