Package org.polkadot.api.promise

Class ApiPromise

  • All Implemented Interfaces:
    Types.ApiBaseInterface<com.onehilltech.promises.Promise>, IApi<com.onehilltech.promises.Promise>
    public class ApiPromise
extends ApiBase<com.onehilltech.promises.Promise>
    # @polkadot/api/promise ## Overview ApiPromise is a standard JavaScript wrapper around the RPC and interfaces on the Polkadot network. As a full Promise-based, all interface calls return Promises, including the static `.create(...)`. Subscription calls utilise `(value) => {}` callbacks to pass through the latest values. The API is well suited to real-time applications where either the single-shot state is needed or use is to be made of the subscription-based features of Polkadot (and Substrate) clients. ## Usage Making rpc calls - ```java import org.polkadot.api.promise.ApiPromise; // initialise via static create ApiPromise api = ApiPromise.create(); // make a subscription to the network head api.rpc.chain.subscribeNewHead((header) => { System.out.print("Chain is at "); System.out.println(header.blockNumber); }); ``` Subscribing to chain state - ```java import org.polkadot.api.promise.ApiPromise; // initialise a provider with a specific endpoint WsProvider provider = new WsProvider("wss://example.com:9944") // initialise via isReady & new with specific provider ApiPromise api = new ApiPromise(provider).isReady; // retrieve the block target time int blockPeriod = api.query.timestamp.blockPeriod().toNumber(); int last = 0; // subscribe to the current block timestamp, updates automatically (callback provided) api.query.timestamp.now((timestamp) => { int elapsed = 0; if(last > 0) elapsed = timestamp - last; last = timestamp.toNumber(); System.out.printf("timestamp %d %d since last %d target", timestamp, elapsed, blockPeriod); }); ``` Submitting a transaction - ```java import org.polkadot.api.promise.ApiPromise; ApiPromise.create().then((api) => { int nonce = api.query.system.accountNonce(keyring.alice.address()); api.tx.balances // create transfer .transfer(keyring.bob.address(), 12345) // sign the transcation .sign(keyring.alice, { nonce }) // send the transaction (optional status callback) .send((status) => { System.out.print("current status "); System.out.println(status.type); }) // retrieve the submitted extrinsic hash .then((hash) => { System.out.print("submitted with hash "); System.out.println(hash); }); }); ```

    • Method Detail

      • create

        public static com.onehilltech.promises.Promise<ApiPromise> create​(IProvider iProvider)
        Creates an ApiPromise instance using the supplied provider. Returns an Promise containing the actual Api instance.
        Parameters:
        provider - provider that is passed to the class contructor. **Example** ```java import org.polkadot.api.promise.ApiPromise; Api.create().then((api) => { int timestamp = await api.query.timestamp.now(); System.out.print("lastest block timestamp "); System.out.println(timestamp); }); ```

      • create

        public static com.onehilltech.promises.Promise<ApiPromise> create()