ERC721 Transfer Event issue

Question

Looking at the open-zeppelin ERC721 Contract's code, I see that the very last thing that its mint function is doing is call emit on the contract's pre-defined Transfer event. My question is: how do I capture and respond to this event in my web3 Dapp?

Here's my code:

    // Set up Event:
    MyApp.NFTtokenTransferEvent = MyApp.NFTContractInstance.Transfer();

    // Now tell my app to LISTEN/WATCH for that Event:
    MyApp.NFTtokenTransferEvent.watch(function (error, result) {
      if (!error) {
        // If a Token was Minted or TRANSFERRED, let us know who, what, where:
        console.log("TRANSFER EVENT RESULTS: " + result);
      }
      else {
        console.log("Error with EVENT and its EMISSION!!! Error is: " + error);
      }
    });
  },

The result I'm getting for is - well, nothing.

When I mint new tokens - which I know is happening successfully cause I am verifying it - I don't get any feedback from the Transfer event. I don't get anything in the result argument - nor do I get any errors. I basically don't get anything.

Any suggestions?

(NOTE: my NFTContract obviously inherits from the ERC721Full Contract, so I'm assuming it/I can access the Transfer event without having to do anything special there, correct? )

Answer 1

I was also facing your issue and was about to post the question when I saw your question. Now I realized what I was doing wrong. I was using the default provider in truffle-config which will be http. You have to use a websocket provider to listen to events. See here https://web3js.readthedocs.io/en/1.0/web3.html#providers.

This fixed the issue for me:

in truffle-config.js

  networks: {
    development: {
      provider: function() {
        return new Web3.providers.WebsocketProvider("ws://localhost:7545");
      },
      network_id: "5777"
    }
  },