kyawsanoo / mmcoin

A sample flutter dapp that interact with solidity smart contract deployed on ethereum TestNet using web3dart package.

mmcoin

A sample flutter dapp that interact with a solidity smart contract deployed on ethereum TestNet using web3dart package.

app ui

The app use sample ui to show balance of MMCoin, deposit and withdraw in interaction of the smart contract.

smart contract info

mmcoin.sol is a smart contract on ethereum TestNet I have compiled and deployed. The app will interact with that contract. Here is the whole contract code:

    // SPDX-License-Identifier: MIT
pragma solidity 0.8.7;
contract MMCoin{
    int balance;

    constructor(){
        balance = 0;
    }

    function getBalance() public view returns (int ) {
        return balance;
    }

    function depositBalance(int depositAmount) public{
        balance = balance + depositAmount;
    }

    function withdrawBalance(int withdrawAmount) public{
        balance = balance - withdrawAmount;
    }
}

abi and smart contract address

Since the app interact with a smart contract, we needs abi of that smart contract to make interaction through. We can find smart contract abi under assets folder named abi.json, you got it when you deployed a smart contract. We also need the smart contract address. Using abi and smart contract address, flutter can load deployed smart contract. Here is the code in flutter:

    Future<DeployedContract> loadContract() async {
  String abi = await rootBundle.loadString("assets/abi.json");
  //print(abi);
  String contractAddress = "0xbF16FFA4860112707d387D12266f51bdC434b754";
  final contract = DeployedContract(ContractAbi.fromJson(abi, "MMCoin"),
      EthereumAddress.fromHex(contractAddress));
  return contract;
}

ethereum client

Since the app interact with smart contract on ethereum testnet, we need to access testnet through ethereum client name Infura. web3dart will connect a JSON rpc API url of your project, you can create it on Infura. I used goerli testnet.
Here is the code in flutter:

   @override
void initState() {
  super.initState();
  httpClient = Client();
  ethClient = Web3Client(
      "https://goerli.infura.io/v3/850bbd87f23c48119f22119992cb901e",
      httpClient);
}

smart contract calls in app

To make a smart contract call with app, we need to change private key of your wallet address. Here is the code in flutter:

   Future<String> submit(String functionName, List<dynamic> args) async {
  EthPrivateKey credential = EthPrivateKey.fromHex(
      "your wallet address private key");
  DeployedContract contract = await loadContract();
  final ethFunction = contract.function(functionName);
  final result = await ethClient.sendTransaction(
      credential,
      Transaction.callContract(
        contract: contract,
        function: ethFunction,
        parameters: args,
        maxGas: 100000,
      ),
      chainId: 5);
  print(result.toString());
  return result;
}

• Remix IDE
• Infura

I followed this tutorial, view the original tutorial, which offers a full reference.