How to get storageKeys for storage subscription?

[poka-IT]

How to use subscribeStorage ? I don't find examples.
I can find the storageKeys on polakdot.js UI, but I don't understand how to get it from this lib?

How to subscribe new blocks, or subscribe to account balance for instance?

duniterApi.rpc.state.subscribeStorage(storageKeysForAccountBalance, (data) {
  print(data.data.free);
});

Thank you!

[leonardocustodio]

You can refer to a sample here: #385 (comment)
But just so you know, may you ever need to subscribe to a storage key; besides being able to look at the Chain State tab on Polkadot-JS, the encodedStorageKey shall you ever need to encode it, it is basically:

Twox128(pallet) + Twox128(method)

Anyway, those should also be available through the lib as in the example above:

[poka-IT]

Thank you, his example works :)

So this is my test code working:

Future<void> startBlockListening() async {
  final storageBlockKeyQuery = [duniterApi.query.system.numberKey()];
  await duniterApi.rpc.state.subscribeStorage(
    storageBlockKeyQuery,
    (storageChangeSet) async {
      final blockNumber = await duniterApi.query.system.number();
      log.d(blockNumber);
    },
  );
}

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

Future<void> startBalanceListening(String address) async {
  if (_addressSubscriptionMap[address] != null) return;
  final accountPubKey = Address.decode(address).pubkey;
  final storageAccountKeyQuery = [
    duniterApi.query.system.accountKey(accountPubKey)
  ];
  _addressSubscriptionMap[address] =
      await duniterApi.rpc.state.subscribeStorage(
    storageAccountKeyQuery,
    (storageChangeSet) async {
      final accountInfo =
          await duniterApi.query.system.account(accountPubKey);
      log.d(accountInfo.data.free);
    },
  );
}

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

But the thing is, here we resend a request for each changes:
final blockNumber = await duniterApi.query.system.number();

Isn't there a way to avoid this by retrieving the correct data directly from storageChangeSet?

[leonardocustodio]

The best way to subscribe to blocks is not to subscribe directly to the storage but to use the RPC.
There are chain_subscribeNewHeads and chain_subscribeFinalizedHeads. You can use either one.
If you are wondering how to do that on Polkadart, you can use the Provider class, initialize it, and call subscribe using the method/args you want.