ERC-20 Token Transfers

Overview

The Dynamic SDK provides methods to send ERC-20 tokens using the web3dart package. You can interact with token contracts to transfer tokens between addresses.

Prerequisites

Dynamic SDK initialized (see Installation Guide)
User authenticated (see Authentication Guide)
EVM wallet available (see Wallet Creation)
dynamic_sdk_web3dart package installed

Send ERC-20 Tokens

import 'package:dynamic_sdk/dynamic_sdk.dart';
import 'package:dynamic_sdk_web3dart/dynamic_sdk_web3dart.dart';
import 'package:web3dart/web3dart.dart';

final sdk = DynamicSDK.instance;

Future<String> sendERC20({
  required BaseWallet wallet,
  required String tokenAddress,
  required String recipient,
  required String amount, // Human-readable amount (e.g., "1.5")
  int decimals = 18,
}) async {
  // Convert human-readable amount to base units
  final baseUnits = parseDecimalToBaseUnits(amount, decimals: decimals);

  // Get network information
  final network = await sdk.wallets.getNetwork(wallet: wallet);
  final chainId = network.intValue()!;

  // Create public client
  final client = sdk.web3dart.createPublicClient(chainId: chainId);

  // Get gas price
  final gasPrice = await client.getGasPrice();

  // Create ERC-20 contract
  final contract = DeployedContract(
    ContractAbi.fromJson(
      '''[
        {
          "constant": false,
          "inputs": [
            {"name": "_to", "type": "address"},
            {"name": "_value", "type": "uint256"}
          ],
          "name": "transfer",
          "outputs": [{"name": "", "type": "bool"}],
          "type": "function"
        }
      ]''',
      'ERC20',
    ),
    EthereumAddress.fromHex(tokenAddress),
  );

  final transferFunction = contract.function('transfer');

  // Create transaction
  final transaction = Transaction.callContract(
    contract: contract,
    function: transferFunction,
    parameters: [
      EthereumAddress.fromHex(recipient),
      baseUnits,
    ],
    maxFeePerGas: EtherAmount.inWei(
      gasPrice.getValueInUnitBI(EtherUnit.wei) * BigInt.from(2),
    ),
    maxPriorityFeePerGas: EtherAmount.inWei(
      gasPrice.getValueInUnitBI(EtherUnit.wei),
    ),
  );

  // Send transaction
  final txHash = await sdk.web3dart.sendTransaction(
    transaction: transaction,
    wallet: wallet,
  );

  print('ERC20 transfer sent!');
  print('Hash: $txHash');
  return txHash;
}

// Helper function to convert decimal string to base units
BigInt parseDecimalToBaseUnits(String value, {required int decimals}) {
  if (decimals < 0 || decimals > 77) {
    throw Exception('Token decimals must be between 0 and 77');
  }

  final parts = value.split('.');
  final wholePart = parts[0].isEmpty ? '0' : parts[0];
  final fracPartRaw = parts.length == 2 ? parts[1] : '';

  final whole = BigInt.tryParse(wholePart);
  if (whole == null) {
    throw Exception('Invalid token amount');
  }

  // Trim fractional part to token's decimal places
  final trimmedFrac = fracPartRaw.substring(
    0,
    fracPartRaw.length > decimals ? decimals : fracPartRaw.length,
  );
  final fracPadded = trimmedFrac.padRight(decimals, '0');
  final frac = fracPadded.isEmpty ? BigInt.zero : (BigInt.tryParse(fracPadded) ?? BigInt.zero);

  return whole * BigInt.from(10).pow(decimals) + frac;
}

import 'package:flutter/material.dart';
import 'package:dynamic_sdk/dynamic_sdk.dart';
import 'package:dynamic_sdk_web3dart/dynamic_sdk_web3dart.dart';
import 'package:web3dart/web3dart.dart';

class SendERC20Widget extends StatefulWidget {
  final BaseWallet wallet;

  const SendERC20Widget({Key? key, required this.wallet}) : super(key: key);

  @override
  State<SendERC20Widget> createState() => _SendERC20WidgetState();
}

class _SendERC20WidgetState extends State<SendERC20Widget> {
  final sdk = DynamicSDK.instance;
  final _tokenAddressController = TextEditingController();
  final _recipientController = TextEditingController();
  final _amountController = TextEditingController();
  final _decimalsController = TextEditingController(text: '18');

  String? txHash;
  bool isLoading = false;
  String? error;

  @override
  void dispose() {
    _tokenAddressController.dispose();
    _recipientController.dispose();
    _amountController.dispose();
    _decimalsController.dispose();
    super.dispose();
  }

  Future<void> _sendTokens() async {
    setState(() {
      isLoading = true;
      error = null;
      txHash = null;
    });

    try {
      final tokenAddress = _tokenAddressController.text.trim();
      final recipient = _recipientController.text.trim();
      final amount = _amountController.text.trim();
      final decimals = int.parse(_decimalsController.text);

      final baseUnits = parseDecimalToBaseUnits(amount, decimals: decimals);

      // Get network information
      final network = await sdk.wallets.getNetwork(wallet: widget.wallet);
      final chainId = network.intValue()!;

      // Create public client
      final client = sdk.web3dart.createPublicClient(chainId: chainId);

      // Get gas price
      final gasPrice = await client.getGasPrice();

      // Create ERC-20 contract
      final contract = DeployedContract(
        ContractAbi.fromJson(
          '''[
            {
              "constant": false,
              "inputs": [
                {"name": "_to", "type": "address"},
                {"name": "_value", "type": "uint256"}
              ],
              "name": "transfer",
              "outputs": [{"name": "", "type": "bool"}],
              "type": "function"
            }
          ]''',
          'ERC20',
        ),
        EthereumAddress.fromHex(tokenAddress),
      );

      final transferFunction = contract.function('transfer');

      // Create transaction
      final transaction = Transaction.callContract(
        contract: contract,
        function: transferFunction,
        parameters: [
          EthereumAddress.fromHex(recipient),
          baseUnits,
        ],
        maxFeePerGas: EtherAmount.inWei(
          gasPrice.getValueInUnitBI(EtherUnit.wei) * BigInt.from(2),
        ),
        maxPriorityFeePerGas: EtherAmount.inWei(
          gasPrice.getValueInUnitBI(EtherUnit.wei),
        ),
      );

      // Send transaction
      final hash = await sdk.web3dart.sendTransaction(
        transaction: transaction,
        wallet: widget.wallet,
      );

      setState(() => txHash = hash);
    } catch (e) {
      setState(() => error = e.toString());
    } finally {
      setState(() => isLoading = false);
    }
  }

  BigInt parseDecimalToBaseUnits(String value, {required int decimals}) {
    final parts = value.split('.');
    final whole = BigInt.tryParse(parts[0]) ?? BigInt.zero;
    final fracRaw = parts.length == 2 ? parts[1] : '';
    final fracPadded = fracRaw.substring(0, fracRaw.length > decimals ? decimals : fracRaw.length).padRight(decimals, '0');
    final frac = BigInt.tryParse(fracPadded) ?? BigInt.zero;
    return whole * BigInt.from(10).pow(decimals) + frac;
  }

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(16.0),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: [
          TextField(
            controller: _tokenAddressController,
            decoration: const InputDecoration(
              labelText: 'Token Contract (0x...)',
              border: OutlineInputBorder(),
            ),
            autocorrect: false,
          ),
          const SizedBox(height: 16),
          TextField(
            controller: _recipientController,
            decoration: const InputDecoration(
              labelText: 'Recipient (0x...)',
              border: OutlineInputBorder(),
            ),
            autocorrect: false,
          ),
          const SizedBox(height: 16),
          Row(
            children: [
              Expanded(
                flex: 2,
                child: TextField(
                  controller: _amountController,
                  decoration: const InputDecoration(
                    labelText: 'Amount',
                    border: OutlineInputBorder(),
                  ),
                  keyboardType: const TextInputType.numberWithOptions(decimal: true),
                ),
              ),
              const SizedBox(width: 8),
              Expanded(
                child: TextField(
                  controller: _decimalsController,
                  decoration: const InputDecoration(
                    labelText: 'Decimals',
                    border: OutlineInputBorder(),
                  ),
                  keyboardType: TextInputType.number,
                ),
              ),
            ],
          ),
          const SizedBox(height: 16),
          ElevatedButton(
            onPressed: isLoading ? null : _sendTokens,
            child: isLoading
                ? const SizedBox(
                    height: 20,
                    width: 20,
                    child: CircularProgressIndicator(strokeWidth: 2),
                  )
                : const Text('Send Tokens'),
          ),
          if (txHash != null) ...[
            const SizedBox(height: 16),
            Text(
              'Success: $txHash',
              style: const TextStyle(fontSize: 12, color: Colors.green),
            ),
          ],
          if (error != null) ...[
            const SizedBox(height: 16),
            Text(
              error!,
              style: const TextStyle(color: Colors.red, fontSize: 12),
            ),
          ],
        ],
      ),
    );
  }
}

Common Token Decimals

Token	Decimals	Notes
ETH, WETH	18	Most ERC-20 tokens use 18
USDC	6	Circle’s USD Coin
USDT	6	Tether USD
WBTC	8	Wrapped Bitcoin
DAI	18	MakerDAO stablecoin

Best Practices

1. Validate Token Address

Always validate the token contract address before sending:

bool isValidEthereumAddress(String address) {
  final pattern = RegExp(r'^0x[a-fA-F0-9]{40}$');
  return pattern.hasMatch(address);
}

// Usage
if (!isValidEthereumAddress(tokenAddress)) {
  throw Exception('Invalid token address');
}

2. Check Token Balance Before Transfer

import 'package:web3dart/web3dart.dart';

Future<BigInt> getTokenBalance({
  required BaseWallet wallet,
  required String tokenAddress,
  required int chainId,
}) async {
  final client = DynamicSDK.instance.web3dart.createPublicClient(chainId: chainId);

  final contract = DeployedContract(
    ContractAbi.fromJson(
      '''[
        {
          "constant": true,
          "inputs": [{"name": "_owner", "type": "address"}],
          "name": "balanceOf",
          "outputs": [{"name": "balance", "type": "uint256"}],
          "type": "function"
        }
      ]''',
      'ERC20',
    ),
    EthereumAddress.fromHex(tokenAddress),
  );

  final balanceFunction = contract.function('balanceOf');

  final result = await client.call(
    contract: contract,
    function: balanceFunction,
    params: [EthereumAddress.fromHex(wallet.address)],
  );

  return result.first as BigInt;
}

3. Use Appropriate Gas Limits

class GasLimits {
  static const int erc20Transfer = 65000; // ERC-20 token transfer
  static const int erc20Approve = 50000; // ERC-20 approve
}

Handle Token Metadata

class TokenMetadata {
  final String name;
  final String symbol;
  final int decimals;

  TokenMetadata({
    required this.name,
    required this.symbol,
    required this.decimals,
  });
}

Future<TokenMetadata> getTokenMetadata({
  required String tokenAddress,
  required int chainId,
}) async {
  final client = DynamicSDK.instance.web3dart.createPublicClient(chainId: chainId);

  final contract = DeployedContract(
    ContractAbi.fromJson(
      '''[
        {
          "constant": true,
          "inputs": [],
          "name": "name",
          "outputs": [{"name": "", "type": "string"}],
          "type": "function"
        },
        {
          "constant": true,
          "inputs": [],
          "name": "symbol",
          "outputs": [{"name": "", "type": "string"}],
          "type": "function"
        },
        {
          "constant": true,
          "inputs": [],
          "name": "decimals",
          "outputs": [{"name": "", "type": "uint8"}],
          "type": "function"
        }
      ]''',
      'ERC20',
    ),
    EthereumAddress.fromHex(tokenAddress),
  );

  final nameResult = await client.call(
    contract: contract,
    function: contract.function('name'),
    params: [],
  );

  final symbolResult = await client.call(
    contract: contract,
    function: contract.function('symbol'),
    params: [],
  );

  final decimalsResult = await client.call(
    contract: contract,
    function: contract.function('decimals'),
    params: [],
  );

  return TokenMetadata(
    name: nameResult.first as String,
    symbol: symbolResult.first as String,
    decimals: (decimalsResult.first as BigInt).toInt(),
  );
}

Next Steps

Send ETH Transactions - Basic ETH transfers
Smart Contract Interactions - Advanced contract calls
Gas Management - Optimize gas usage
Token Balances - Query token balances

Getting Started

Authentication

Wallets

Gasless

Flutter Specific

SDK Reference

ERC-20 Token Transfers

Overview

Prerequisites

Send ERC-20 Tokens

Complete ERC20 Transfer Widget

Common Token Decimals

Best Practices

1. Validate Token Address

2. Check Token Balance Before Transfer

3. Use Appropriate Gas Limits

Handle Token Metadata

Next Steps

Getting Started

Authentication

Wallets

Gasless

Flutter Specific

SDK Reference

​Overview

​Prerequisites

​Send ERC-20 Tokens

​Complete ERC20 Transfer Widget

​Common Token Decimals

​Best Practices

​1. Validate Token Address

​2. Check Token Balance Before Transfer

​3. Use Appropriate Gas Limits

​Handle Token Metadata

​Next Steps

Overview

Prerequisites

Send ERC-20 Tokens

Complete ERC20 Transfer Widget

Common Token Decimals

Best Practices

1. Validate Token Address

2. Check Token Balance Before Transfer

3. Use Appropriate Gas Limits

Handle Token Metadata

Next Steps