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Hello World!

Ryan edited this page Feb 15, 2019 · 6 revisions

Hello World!

This code sample is minimalistic. It's goal is to demonstrate how to wire up an application with the XAYA platform quickly and easily.

HelloXaya is a typical "Hello World!" example. It wires up the XAYA platform in a Windows forms project.

HelloXaya lets you say "Hello World!" on the XAYA blockchain. That's all it does.

Download the HelloXaya project here.

NOTE: The only file that is important for this tutorial is "HelloXaya.cs". It would be best to open the solution in Visual Studio, then open the HelloXaya.cs form and it's code. Nothing else is needed to understand the basics of wiring up libxayagame, sending moves and getting data.

Follow along with the tutorial here and you'll be in a solid position to get into more advanced topics. Don't get distracted with other parts of the code.

Get a XAYA Wallet

You'll need a XAYA wallet and some CHI.

To start, download and install the latest XAYA Electron wallet here if you're on Windows, or the the XAYA QT wallet if you're on Linux or Mac. The wallets automatically run the XAYA daemon, i.e. xayad. (This tutorial assumes Windows.)

If you run the QT or xayad, you'll need to set flags manually. They're automatically set in the Electron wallet. For more information on flags, see the Daemon Flags tutorial.

Run the wallet or xayad and give it time to fully synchronise.

You should also get some CHI. You can buy CHI at Liquid.com or ask in the Development forum. 1 CHI is lots more than enough to get started.

Inside HelloXaya

There are 4 distinct elements inside of HelloXaya.

  • HelloXaya project: This is our "game"
  • BitcoinLib project: This is used for RPCs
  • XAYAWrapper project: This wraps the C++ 64-bit libxayagame statically linked libarary in the XayaStateProcessor folder
  • XayaStateProcessor folder: This has the precompiled libxayagame binary for Windows, libxayawrap.dll, and all its dependencies

While this tutorial only explains HelloXaya, you can find more information about other elements elsewhere in the XAYA documentation and tutorials.

Important Considerations

VIDEO Set your XAYA project to 64 bit

Set your XAYA project to 64 bit

The XAYAWrapper DLL (libxayawrap.dll) is 64-bit. Consequently, your project MUST exclude 32-bit or explicitly be set as 64-bit. See this HelloXaya setting:

Uncheck Prefer 32-bit

Otherwise, you must set your project to be 64-bit (x64).

x64

Implementing XAYA Simplified

VIDEO Simplified overview of implementing XAYA

Simplified overview of implementing XAYA

To implement XAYA, all you need to do is to is:

  • Instantiate XAYAWraper (1 line of code)
  • Connect to XAYAWrapper (1 line of code)
  • Set up a listener thread to receive game states
  • Implement game logic in:
    • 3 callbacks
      • initialCallbackResult (20 lines of trivial code)
      • forwardCallbackResult
      • backwardCallbackResult
    • Ancillary game logic
      • JSON classes
      • Helper methods
  • Send moves to the XAYA blockchain
    • This requires RPCs (can be implemented in many ways)

Threading

It's crucial that you create threads for XAYAWrapper.

Portions of XAYAWrapper are blocking operations and MUST be run in separate threads. Specifically, the XAYAWrapper.xayaGameService.WaitForChange and XAYAWrapper.Connect methods.

Threading in HelloXaya

In HelloXaya, we've used BackgroundWorkers. There are more robust threading patterns available, but BackgroundWorkers are simple to understand with little complexity.

You can implement better threading structures on your own.

Instantiate and Connect to XAYAWrapper

VIDEO Instantiate and Connect to XAYAWrapper

Instantiate and Connect to XAYAWrapper

Instantiating and Connecting to XAYAWrapper must be done in a thread. The connection is a blocking operation.

However, once connected, XAYAWrapper will immediately begin sending log data to the console and game state data to the listener, i.e. through calling the XAYAWrapper.xayaGameService.GetCurrentState method. The log data isn't game state data though; that is examined below.

To instantiate the wrapper, call it's constructor:

wrapper = new XayaWrapper(dataPath, // The path to the game's executable file. 
	Properties.Settings.Default.Host, // The host, e.g. localhost or 127.0.0.1
	"8900", // The game host port. Can be any free port.
	ref result, // An error or success message.
	CallbackFunctions.initialCallbackResult, 
	CallbackFunctions.forwardCallbackResult, 
	CallbackFunctions.backwardCallbackResult);

To connect, call the Connect method:

result = wrapper.Connect(dataPath, // The path to the game's executable file. 
	FLAGS_xaya_rpc_url, // The URL for RPC calls.
	"8900",  // The game host port. Can be any free port.
	"0", // Which network to use: Mainnet, Testnet, or Regtestnet.
	"memory", // The storage type: memory, sqlite, or lmdb.
	"helloworld", // The name of the game in the 'g/' namespace.
	dataPath + "\\..\\XayaStateProcessor\\database\\", // Path to the database folder, e.g. SQLite.
	dataPath + "\\..\\XayaStateProcessor\\glogs\\"); // Path to glog output folder.

Listening for New GameStates

VIDEO Listening for new GameStates

Listening for new GameStates

We must listen for updates in a thread. There are 4 important lines of code.

In our listener, we use the wrapper to get game states. The first thing to do is to tell the wrapper to wait until there's a new game state.

wrapper.xayaGameService.WaitForChange();

Once there's a game state, the thread resumes and we get the game state.

BitcoinLib.Responses.GameStateResult actualState = 
	wrapper.xayaGameService.GetCurrentState();

We then cast that as a GameState by deserialising the JSON.

state = JsonConvert.DeserializeObject<GameState>(actualState.gamestate);

The final step in our listening thread is to send the game state to the main UI thread.

sendingWorker.ReportProgress(0, state);

Update the UI with the New GameState

VIDEO Update the UI with the New GameState

Update the UI with the New GameState

Our listener thread casts the event argument as a GameState and sends it to a method that updates the game.

UpdateHelloChat((GameState)e.UserState);

HelloXaya merely updates a text box with what other people have said. It loops through all players and stores data in a StringBuilder.

sb.AppendLine(v.Key + " said \"" + v.Value.hello + "\"");

We then update the textbox in the UI.

txtHelloGameState.Text = sb.ToString();

Sending Moves to the Blockchain

VIDEO Sending Moves to the Blockchain

Sending Moves to the Blockchain

You don't need to be running an instance of a game to send moves.

Moves can be sent arbitrarily in many ways. Here are some ways:

  • From xaya-cli
  • From the XAYA QT console
  • Sending to xayad
  • Etc.

When processing moves, you must guard against invalid moves with robust error checking. See the code for example error checks.

In HelloXaya, we build the move in a string then send it:

string hello = "{\"g\":{\"helloworld\":{\"m\":\"" + txtHelloWorld.Text + "\"}}}";
xayaService.NameUpdate(this.cbxNames.GetItemText(this.cbxNames.SelectedItem), 
	hello, 
	new object());

Done!

Try running HelloXaya and then say hello to everyone!

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