在 React 组件中渲染返回的 Solidity 映射值

Question

Here is a Solidity contract:

pragma solidity ^0.8.7;

contract SomeContract {

  address public manager;
  uint public theNumberNine;
  mapping (string => mapping (address => uint)) public stringToAddrToInt;

  constructor() {
    manager = msg.sender;
    theNumberNine = 9;
  }

  function setInt(string memory someString) public {
    stringToAddrToInt[someString][msg.sender] = theNumberNine;
  }

  function getIntFromMapping(string memory someString) public view returns (uint) {
    return stringToAddrToInt[someString][msg.sender];
  }
}

Here is a JSX frontend:

import React, { Component } from 'react';
import { Button } from 'semantic-ui-react';
import SomeContract from 'someContract';
import Web3 from 'web3';

class SomeClass extends Component {
  static async getInitialProps(props) {
    const { address, myString } = props.query;
    const contractInstance = SomeContract(address);
    const provider = new Web3.providers.HttpProvider(
      'https://kovan.infura.io/my-endpoint-here'
    );
    const web3 = new Web3(provider);
    const accounts = await web3.eth.getAccounts();
    await contractInstance.methods.setInt(myString).send({
      from: accounts[0]
    });
    const intFromSolidity = await contractInstance.methods.getIntFromMapping(myString).call();

    return { intFromSolidity };
  }

  onSubmit = async () => {
    console.log(this.props.intFromSolidity);
  }

  render() {
    return (
      <Button basic onClick={this.onSubmit}>
        I should output 9
      </Button>
    );
  }
}

Expected output: 9
Actual output: undefined

The console log is undefined, but when calling getIntFromMapping in Remix, it outputs 9 as expected. I would appreciate a little enlightenment on the reason for this behavior, and how to properly return solidity mapping values for use in React components.

Answer 1

Depending on next.js version that you are using, you might need to return from initialProps like this

return { props:{intFromSolidity} }