Meetup RSK-Xablu

Goal start your mobil development with Xamarin

Blockchain for developer

This repository show how to start coding in RSK in mobile apps

Speakers Dulce Villarreal Dulce is a Developer Advocate with RSK on the San Francisco City Team focusing on Blockhain and Fintech. With a background in economie she works with startups and developers to help them adopt Blockchain and Fintech, talks at industry events and spends her weekends at hackathons.

Sebastian Perez Mobile & Blockchain Developer. Microsoft MVP. Enthusiast of disruptive technologies, looking for innovational projects that generate a positive impact on society. Software developer since more than 10 years, with experience in Web, Mobile and Blockchain. Sportsman, basketball fan.

Agenda:

6:00 pm Latinx food and networking 6:30 pm Discussion: Mobile Apps Security 7:00 pm Worshop: using Nethereum to connect to a RSK-node 7:30 pm Q&A 8:30 Wrap up

Outline

Requirements:

Workshop:

Visual Studio Community 2019 installed with Xamarin
Add Android SDK & emulator

Important URLS:

https://visualstudio.microsoft.com/vs/community/ http://rsk.co

Prerequisites

Basic development knowledge.

Workshop

Open Visual Studio, and Create a new Blank Form Apps (Cross Platform)
Check that Xamarin.Essentials is installed. If not, then install it from NuGet.
Edit Main Page StackLayout Tag:

  <StackLayout>
    <Entry Placeholder="Address" x:Name="entryAddress" />
    <Entry Placeholder="Key" x:Name="entryKey" />
    <Button Text="Store" Clicked="StoreKey"/>
  </StackLayout>

Edit Main.xaml.cs, adding:

  async void StoreKey(System.Object sender, System.EventArgs e)
  {
      try
      {
          await SecureStorage.SetAsync("user-address", entryAddress.Text);
          await SecureStorage.SetAsync("user-key", entryKey.Text);
          await Navigation.PushAsync(new AccountPage());
      }
      catch (Exception exc)
      {
          await DisplayAlert("Error","There was a problem storing user information","OK");
      }
  }

Override this method:

protected async override void OnAppearing()
{
    base.OnAppearing();

    if (await SecureStorage.GetAsync("user-address") != null)
        await Navigation.PushAsync(new AccountPage());
}

Create a new ContentPage called "AccountPage", then edit construtor:

Web3 web3;

public AccountPage()
{
    InitializeComponent();

    web3 = new Web3("https://public-node.testnet.rsk.co");
}

Install Nethereum from NuGet
Get your account balance:

protected async override void OnAppearing()
{
    base.OnAppearing();
    var userAddress = await SecureStorage.GetAsync("user-address");
    var blockNumber = web3.Eth.Blocks.GetBlockNumber.SendRequestAsync();
    var balance = await web3.Eth.GetBalance.SendRequestAsync(userAddress);
    LabelBalance.Text = balance.Value.ToString();
}

Send transaction:

async void Send_Clicked(System.Object sender, System.EventArgs e)
{
    var userKey = await SecureStorage.GetAsync("user-key");
    var userAddress = await SecureStorage.GetAsync("user-address");
    Account account = new Account(userKey);
    account.NonceService = new InMemoryNonceService(account.Address, web3.Client);
    var futureNonce = await account.NonceService.GetNextNonceAsync();
    var transactionInput = new TransactionInput
    {
        From = userAddress,
        To = entryAddressTo.Text,
        Value = new HexBigInteger(new BigInteger(100))
    };
    var txSigned = new Nethereum.Signer.TransactionSigner();
    var signedTx = txSigned.SignTransaction(userKey, transactionInput.To, transactionInput.Value, futureNonce);
    var transaction = new Nethereum.RPC.Eth.Transactions.EthSendRawTransaction(web3.Client);
    var txHash = await transaction.SendRequestAsync(signedTx);
    await DisplayAlert("Transaction Sent","You tx was sent. Hash: " + txHash, "OK");
}

Edit AccountPage.xaml

<StackLayout>
    <Label Text="Balance" />
    <Label x:Name="LabelBalance" />

    <Entry Placeholder="Send funds to..." x:Name="entryAddressTo" />
    <Button Text="Send" Clicked="Send_Clicked" />
</StackLayout>

That's all :)

dulcedu/MeetupRSKXablu