Invocation Transaction example required about neow3j

[gsmachado]

The contract invocation feature is implemented since neow3j version 2.0.0. Check it out for the latest release here.

Anyway, I'm attaching here an example based on neow3j version 2.0.1:

import io.neow3j.contract.ContractInvocation;
import io.neow3j.contract.ContractParameter;
import io.neow3j.protocol.Neow3j;
import io.neow3j.protocol.core.methods.response.InvocationResult;
import io.neow3j.protocol.exceptions.ErrorResponseException;
import io.neow3j.protocol.http.HttpService;
import io.neow3j.transaction.InvocationTransaction;
import io.neow3j.wallet.Account;

import java.io.IOException;
import java.math.BigDecimal;

public class ContractInvocationExample {

    public static void main(String[] args) throws IOException, ErrorResponseException {

        // Crate a connection to an RPC node.
        Neow3j neow3j = Neow3j.build(new HttpService("https://node2.neocompiler.io"));

        // The script hash of the deployed contract. In this case it is the name service smart
        // contract found at this link
        // https://github.com/CityOfZion/python-smart-contract-workshop/blob/master/4-domain.py
        String contractScriptHash = "1a70eac53f5882e40dd90f55463cce31a9f72cd4";

        // Instantiate your account. It will be the originator of the contract invocation.
        Account acct = Account.fromWIF("KxDgvEKzgSBPPfuVfw67oPQBSjidEiqTHURKSDL1R7yGaGYAeYnr").build();

        // Fetch the account's balances. This is needed to pay for potential fees in the invocation.
        acct.updateAssetBalances(neow3j);

        // Build the ContractInvocation according to your needs.
        ContractInvocation invoc = new ContractInvocation.Builder(neow3j)
                .contractScriptHash(contractScriptHash)
                .account(acct)
                // Add parameters in the correct order as they are expected by the contract.
                .parameter(ContractParameter.string("register"))
                .parameter(ContractParameter.array(
                        ContractParameter.string("neow3j.com"),
                        ContractParameter.byteArrayFromAddress(acct.getAddress())))
                // You can add a network fee for priority. Your account needs to own the GAS for it.
                .networkFee(new BigDecimal("0.1"))
                .build();

        // You can get the invocation transaction object if you for example need to create a custom
        // signature from it.
        InvocationTransaction tx = invoc.getTransaction();

        // If you don't need a special signature, simply let the transaction be signed with the
        // account given above.
        invoc.sign();

        // And finally perform the invocation. The RPC node doesn't inform us about the result of
        // the invocation. Therefore this call does not return any information about the call results.
        invoc.invoke();

        // You can also run a test invocation which gives you the GAS consumption of your invocation
        // and the return value that the contract produces when invoked. BUT be careful! If the
        // invocation runs trough a CheckWitness() method call in the smart contract it will fail
        // and return VM state FAULT. This does not mean that your invocation with invoc.incoke()
        // fails. It is just because in this test invoke it is not possible to provide the
        // information for completing the witness check.
        InvocationResult result = invoc.testInvoke();
    }
}