こんにちは！友好的な注意点：このページは、 Dart/Flutter リクエストの操作に関する確かな概要を提供することを目的としています。実践的なコード例については、 API Methods documentation をチェックしてください。そこにはすべてのサポートされている言語ですぐに使用できる例があります！

# Web3Dart Library

The primary Ethereum library for Dart and Flutter ecosystems, providing comprehensive blockchain interaction capabilities.

import 'package:web3dart/web3dart.dart';
import 'package:http/http.dart';

class EthereumService {
  final Web3Client client;

  EthereumService(String rpcUrl) : client = Web3Client(rpcUrl, Client());

  Future<EtherAmount> getBalance(String address) async {
    final addr = EthereumAddress.fromHex(address);
    return await client.getBalance(addr);
  }

  Future<String> sendTransaction({
    required Credentials credentials,
    required String to,
    required BigInt amount,
  }) async {
    final transaction = await client.sendTransaction(
      credentials,
      Transaction(
        to: EthereumAddress.fromHex(to),
        value: EtherAmount.fromBigInt(EtherUnit.wei, amount),
      ),
    );
    return transaction;
  }
}

GitHub: web3dart
Pub.dev: web3dart package
Features:
- Flutter support for cross-platform mobile dApps
- Seamless integration with Flutter widgets
- Complete contract interaction capabilities
- Secure transaction signing and verification
- HD wallet integration with BIP-39/44 support
- ENS resolution and integration
- ERC-20 and ERC-721 token standards support
- Gas estimation and optimization

Important Note: Always specify a gas limit when creating transactions to prevent unexpected transaction failures. The Web3Dart library will attempt to estimate gas but explicit values are recommended for production applications.

# Flutter Integration Examples

Example of a Flutter widget using Web3Dart to display wallet balance:

import 'package:flutter/material.dart';
import 'package:web3dart/web3dart.dart';

class WalletWidget extends StatefulWidget {
  @override
  _WalletWidgetState createState() => _WalletWidgetState();
}

class _WalletWidgetState extends State<WalletWidget> {
  final ethereum = EthereumService('YOUR_ETHEREUM_NODE_URL');
  EtherAmount? balance;

  Future<void> updateBalance() async {
    final newBalance = await ethereum.getBalance('YOUR_ADDRESS');
    setState(() {
      balance = newBalance;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Card(
      child: Padding(
        padding: EdgeInsets.all(16.0),
        child: Column(
          children: [
            Text('Balance: ${balance?.getValueInUnit(EtherUnit.ether)} ETH'),
            ElevatedButton(
              onPressed: updateBalance,
              child: Text('Refresh Balance'),
            ),
          ],
        ),
      ),
    );
  }
}

Performance Tip: For production Flutter apps, consider implementing caching mechanisms and background refresh patterns to avoid excessive RPC calls that might impact app responsiveness.

# Smart Contract Integration

Working with smart contracts in Dart with complete type safety:

class SmartContractService {
  final Web3Client client;
  final DeployedContract contract;

  SmartContractService(String rpcUrl, String contractAddress, String abi)
      : client = Web3Client(rpcUrl, Client()),
        contract = DeployedContract(
          ContractAbi.fromJson(abi, 'YourContract'),
          EthereumAddress.fromHex(contractAddress),
        );

  Future<List<dynamic>> callFunction(
    String functionName,
    List<dynamic> params,
  ) async {
    final function = contract.function(functionName);
    final result = await client.call(
      contract: contract,
      function: function,
      params: params,
    );
    return result;
  }
}

Security Note: When handling private keys in Flutter applications, use secure storage solutions like flutter_secure_storage to protect sensitive credentials. Never hardcode private keys in your application code.

# Error Handling and Utilities

Proper error handling in Dart for robust Ethereum applications:

class EthereumException implements Exception {
  final String message;
  final dynamic originalError;

  EthereumException(this.message, [this.originalError]);

  @override
  String toString() => 'EthereumException: $message';
}

extension EtherAmountExtension on EtherAmount {
  String formatEther([int decimals = 4]) {
    return getValueInUnit(EtherUnit.ether).toStringAsFixed(decimals);
  }
}

Dart & Flutter Tools for Ethereum

# Web3Dart Library

# Flutter Integration Examples

# Smart Contract Integration

# Error Handling and Utilities

See also