public IObservable <string> CreateAndAnnounceTransaction(ProximaxMessagePayloadModel messagePayload,
string signerPrivateKey,
string recipientPublicKey, string recipientAddress, int transactionDeadline,
List <Mosaic> transactionMosaics, bool useBlockchainSecureMessage)
{
CheckParameter(signerPrivateKey != null, "signerPrivateKey is required");
CheckParameter(messagePayload != null, "messagePayload is required");
var message = BlockchainMessageService.CreateMessage(messagePayload, signerPrivateKey,
recipientPublicKey, recipientAddress, useBlockchainSecureMessage);
var recipient = GetRecipient(signerPrivateKey, recipientPublicKey, recipientAddress);
var transaction = CreateTransaction(recipient, transactionDeadline, transactionMosaics, message);
var signedTransaction = NemUtils.SignTransaction(signerPrivateKey, transaction);
TransactionClient.Announce(signedTransaction, NemUtils.GetAddressFromPrivateKey(signerPrivateKey));
return(Observable.Return(signedTransaction.Hash));
}