How subscribe to balance changes?

[raqeta]

Hi, I want to subscribe to balance changes. I want to receive the balance in an event or trigger an event about a change, increase or decrease in the balance. Could you tell me how I can do this? I didn't find this in the documentation. Thanks.

[leonardocustodio]

Hello, I believe you can subscribe to the storage key system.accounts, let me know if it works out.

[raqeta]

I've tried to do it like in code below.
Should I add System and Account? Is it right launch point to subscribe?
And also I didn't get any updates and I suppose I have some mistakes with address encoding.

Future startBalanceListening(String address, Function(BalanceData) onUpdate) async {
// address for example == '5GTCTWCBQ797s8cf9KFBgAGQgpwdAHnoy37aTT1PgC37PEEN'
final account = Address.decode(address);
_subscription = await _myDot.rpc.state.subscribeStorage(
[account.pubkey], // should I add ['System', 'Account'] here and how ?
(set) async {
// do something after changing
},
);
}

[leonardocustodio]

system.account is the storage key, it will subscribe to all balance changes of every account. If you want a specific account would be system.account(the account). I'm not in the computer right now so can't write a sample for you but I can do it in a few hours.

[raqeta]

thanks, I'll try :)

[raqeta]

Thanks to your help, chatGpt and official Polkadot.js documentation I find out everything work correct with this code :)

  final MyChainDot _myChainDot;
  final Map<String, StreamSubscription<StorageChangeSet>> _addressSubscriptionMap = {};

  @override
  Future<void> startBalanceListening(String? address, Function(BalanceData) onUpdate) async {
    if (address == null || address.isEmpty || _addressSubscriptionMap[address] != null) return;
    final accountPubKey = Address.decode(address).pubkey;
    final storageAccountKeyQuery = [_myChainDot.query.system.accountKey(accountPubKey)];
    _addressSubscriptionMap[address] = await _myChainDot.rpc.state.subscribeStorage(
      storageAccountKeyQuery,
      (storageChangeSet) async {
        final accountInfo = await _myChainDot.query.system.account(accountPubKey);
        onUpdate.call(
          BalanceData(
            accountId: address,
            accountNonce: accountInfo.nonce,
            availableBalance: (accountInfo.data.free + accountInfo.data.reserved + accountInfo.data.frozen),
          ),
        );
      },
    );
  }

  @override
  Future<void> stopBalancesListening(String? address) async {
    if (address == null || address.isEmpty || _addressSubscriptionMap[address] == null) return;
    final subscription = _addressSubscriptionMap[address];
    if (subscription == null) return;
    _addressSubscriptionMap.remove(address);
    await subscription.cancel();
  }

[leonardocustodio]

Great, glad it helped