near_contract_standards::non_fungible_token::core

Trait NonFungibleTokenResolver

Source 
pub trait NonFungibleTokenResolver {
    // Required method
    fn nft_resolve_transfer(
        &mut self,
        previous_owner_id: AccountId,
        receiver_id: AccountId,
        token_id: TokenId,
        approved_account_ids: Option<HashMap<AccountId, u64>>,
    ) -> bool;
}
Expand description

Used when an NFT is transferred using nft_transfer_call. This is the method that’s called after nft_on_transfer. This trait is implemented on the NFT contract.

§Examples

use std::collections::HashMap;
use near_sdk::{PanicOnDefault, AccountId, PromiseOrValue, near};
use near_contract_standards::non_fungible_token::{NonFungibleToken, NonFungibleTokenResolver, TokenId};

#[near(contract_state)]
#[derive(PanicOnDefault)]
pub struct Contract {
   tokens: NonFungibleToken,
}
#[near]
impl NonFungibleTokenResolver for Contract {
    #[private]
    fn nft_resolve_transfer(&mut self, previous_owner_id: AccountId, receiver_id: AccountId, token_id: TokenId, approved_account_ids: Option<HashMap<AccountId, u64>>) -> bool {
        self.tokens.nft_resolve_transfer(previous_owner_id, receiver_id, token_id, approved_account_ids)
    }
}

Required Methods§

Source

fn nft_resolve_transfer( &mut self, previous_owner_id: AccountId, receiver_id: AccountId, token_id: TokenId, approved_account_ids: Option<HashMap<AccountId, u64>>, ) -> bool

Finalize an nft_transfer_call chain of cross-contract calls.

The nft_transfer_call process:

  1. Sender calls nft_transfer_call on FT contract
  2. NFT contract transfers token from sender to receiver
  3. NFT contract calls nft_on_transfer on receiver contract 4+. [receiver contract may make other cross-contract calls] N. NFT contract resolves promise chain with nft_resolve_transfer, and may transfer token back to sender

Requirements:

  • Contract MUST forbid calls to this function by any account except self
  • If promise chain failed, contract MUST revert token transfer
  • If promise chain resolves with true, contract MUST return token to sender_id

Arguments:

  • previous_owner_id: the owner prior to the call to nft_transfer_call
  • receiver_id: the receiver_id argument given to nft_transfer_call
  • token_id: the token_id argument given to ft_transfer_call
  • approved_account_ids: if using Approval Management, contract MUST provide set of original approved accounts in this argument, and restore these approved accounts in case of revert.

Returns true if token was successfully transferred to receiver_id.

Implementors§