Polkadart

Polkadart is the most comprehensive Dart/Flutter SDK for interacting with Polkadot, Substrate, and other compatible blockchain networks. Designed with a Dart-first approach and type-safe APIs, it provides everything developers need to build powerful decentralized applications.

This page will outline some of the core components of Polkadart. For more details, refer to the official documentation.

Installation

Add Polkadart to your pubspec.yaml:

All packages

dart pub add polkadart polkadart_cli polkadart_keyring polkadart_scale_codec secp256k1_ecdsa sr25519 ss58 substrate_bip39 substrate_metadata

Core only

dart pub add polkadart polkadart_cli polkadart_keyring

For type-safe API generation, add the following to your pubspec.yaml:

pubspec.yaml

polkadart:
  output_dir: lib/generated
  chains:
    polkadot: wss://rpc.polkadot.io
    kusama: wss://kusama-rpc.polkadot.io
    custom: wss://your-node.example.com

Get Started

Type Generation

Polkadart provides a CLI tool to generate type definitions from any Polkadot-SDK compatible blockchain network. This allows you to build type-safe Dart applications without dealing with the low-level details of the blockchain.

Run Generator

dart run polkadart_cli:generate -v

Use Generated Types

import 'package:your_app/generated/polkadot/polkadot.dart';
import 'package:polkadart/polkadart.dart';
import 'package:ss58/ss58.dart';

final provider = Provider.fromUri(Uri.parse('wss://rpc.polkadot.io'));
final polkadot = Polkadot(provider);

// Account from SS58 address
final account = Address.decode('19t9Q2ay58hMDaeg6eeBhqmHsRnc2jDMV3cYYw9zbc59HLj');

// Retrieve Account Balance
final accountInfo = await polkadot.query.system.account(account.pubkey);
print('Balance: ${accountInfo.data.free}')

Creating an API Instance

An API instance is required to interact with the blockchain. Polkadart provides a Provider class that allows you to connect to any network.

import 'package:demo/generated/polkadot/polkadot.dart';
import 'package:polkadart/provider.dart';

Future<void> main(List<String> arguments) async {
  final provider = Provider.fromUri(Uri.parse('wss://rpc.polkadot.io'));
  final polkadot = Polkadot(provider);
}

Reading Chain Data

Besides querying the data using the query from the generated API, you can also use the State API for querying storage data, metadata, runtime information, and other chain information.

final stateApi = StateApi(provider);

// Get current runtime version
final runtimeVersion = await stateApi.getRuntimeVersion();
print(runtimeVersion.toJson());

// Get metadata
final metadata = await stateApi.getMetadata();
print('Metadata version: ${metadata.version}');

Subscribe to New Blocks

You can subscribe to new blocks on the blockchain using the subscribe method.

final subscription = await provider.subscribe('chain_subscribeNewHeads', []);

subscription.stream.forEach((response) {
  print('New head: ${response.result}');
});

Send a Transaction

Perhaps the most common operation done in any blockchain is transferring funds. Here you can see how that can be done using Polkadart:

final wallet = await KeyPair.sr25519.fromUri("//Alice");
print('Alice\' wallet: ${wallet.address}');

// Get information necessary to build a proper extrinsic
final runtimeVersion = await polkadot.rpc.state.getRuntimeVersion();
final currentBlockNumber = (await polkadot.query.system.number()) - 1;
final currentBlockHash = await polkadot.query.system.blockHash(currentBlockNumber);
final genesisHash = await polkadot.query.system.blockHash(0);
final nonce = await polkadot.rpc.system.accountNextIndex(wallet.address);

// Make the encoded call
final multiAddress = $MultiAddress().id(wallet.publicKey.bytes);
final transferCall = polkadot.tx.balances.transferKeepAlive(dest: multiAddress, value: BigInt.one).encode();

// Make the payload
final payload = SigningPayload(
    method: transferCall,
    specVersion: runtimeVersion.specVersion,
    transactionVersion: runtimeVersion.transactionVersion,
    genesisHash: encodeHex(genesisHash),
    blockHash: encodeHex(currentBlockHash),
    blockNumber: currentBlockNumber,
    eraPeriod: 64,
    nonce: nonce,
    tip: 0,
).encode(polkadot.registry);

// Sign the payload and build the final extrinsic
final signature = wallet.sign(payload);
final extrinsic = ExtrinsicPayload(
  signer: wallet.bytes(),
  method: transferCall,
  signature: signature,
  eraPeriod: 64,
  blockNumber: currentBlockNumber,
  nonce: nonce,
  tip: 0,
).encode(polkadot.registry, SignatureType.sr25519);

// Send the extrinsic to the blockchain
final author = AuthorApi(provider);
await author.submitAndWatchExtrinsic(extrinsic, (data) {
  print(data);
});

Where to Go Next

To dive deeper into Polkadart, refer to the official Polkadart documentation, where you can find comprehensive guides for common use cases and advanced usage.