如何监听 Flow 区块链上的智能合约中的事件？

Question

我使用了一些服务来监听以太坊上智能合约中的事件。但我找不到任何与使用 Flow Blockchain 时类似的文档。我怎样才能做到这一点？

Answer 1

对于一项常见任务来说，这是一个非常好的问题！ @onflow/fcl包为您提供了一个有用的方法events，可用于“订阅”特定事件。您可以在 Flow Docs 站点上查看事件描述。或者您可以复制/粘贴下面的代码并使用它：

import * as fcl from "@onflow/fcl";

// We need to point FCL to some access node.
// We will use Mainnet REST endpoint for this, as the contract
// we want to listen to is deployed there

fcl.config({
  "accessNode.api": "https://rest-mainnet.onflow.org",
  // we will set the poll rate for events to 3 seconds
  "fcl.eventPollRate": 3000
});

// FlowFees is the most active contract, since every transaction will
// trigger "FeesDeducted" event, so it will be easier to see that our code
// is working correctly
const contractAddress = "f919ee77447b7497";
const contractName = "FlowFees";
const eventName = "FeesDeducted";

// Event name consist of 2 or 4 parts
// 2 part event name have only system events
// For deployed contract, event should be constructed from 4 parts
// - "A" prefix, stands for "account"
// - address where contract, holding definition of event is deployed
// - contract name
// - event name
const event = `A.${contractAddress}.${contractName}.${eventName}`;

console.log(
  `Listening for event "${eventName}" from "${contractName}" deployed on account 0x${contractAddress}`
);
fcl.events(event).subscribe((eventData) => {
  console.log(eventData);
});

您还可以尝试使用Codesandbox 示例