KOTLIN CORE SDK

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Getting Started

This is a simple integration guide for the XYO Core Kotlin Library. We do recommend experience with Kotlin and Android development but have included guides to get you started.

For the source code from this guide refer to this link

For the complete XYO Core Kotlin SDK on GitHub refer to this link

Table of Contents

App Structure

  • Kotlin with Android Studio

Click here for an introduction from Google

Versions used in this sample

  • Android Studio 3.4.2
  • Java 12.0.1

Using Android Studio

We are using Android Studio to create this simple app, make sure it is updated to the latest versions.

Virtual Device Emulator

When creating the configuration for the emulator, we recommend using a mid-range device definition for a wider range of coverage for android devices. (Such as a Pixel 3a, Samsung Galaxy S10e) feel free to use whatever example Android device you would like.

This sample app is best for mobile devices

This Sample App Example is best for mobile devices since bound witnessing is optimal on mobile. Integration into your application should be based on a mobile app architecture.

For this app we will only use one screen with one activity.

Please note that the complete code for part one of this guide is in the Sample folder. We encourage you to go through this tutorial to better understand the process of creating an origin chain utilizing this sdk.

Create the project

  1. Open Android Studio

  2. In the main Welcome to Android Studio dialog, click Start a new Android Studio project

  3. In the New Project dialog, give your application a name

  4. Go ahead and accept the defaults

  5. Check the box that includes Kotlin support

  6. Accept default location, then click Next

  7. In the Target Android Devices dialog, accept the defaults. Click Next

  8. Select Empty Activity. Click Next

  9. In the Customize the Activity dialog, accept the defaults

  10. Click Finish

Briefly examine the file structure. If you need a refresher, please refer to the aforementioned Google Introduction

We also recommend that you run your app on a physical device (if you have one available) otherwise you could use an emulator.

There are two gradle scripts in Android Studio that you will need to update. Please note that these are additions and not meant to replace anything generated from Android Studio

build.gradle: (Project: YourAppName ) as seen in the android studio project structure

allProjects {
  repositories {
    mavenCentral()
    maven {
      url  "https://dl.bintray.com/xyoraclenetwork/xyo"
    }
  }
}

build.gradle (Module: app) as seen in the android studio project structure

dependencies {
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.2.0"
    implementation "network.xyo:sdk-core-kotlin:3.0.3"
    implementation "org.bouncycastle:bcpkix-jdk15on:1.58"
}

// you may need to include this 

packagingOptions {
    exclude 'META-INF/atomicfu.kotlin_module'
}

Project Design

Since this is a simple app, we won't need to do much design, we are only creating a button to create, sign and display an origin chain hash.

Code or design: your choice

If you are an experienced Android developer, you will already have your process.

activity_main.xml

Here is the code you should start up with, which has an empty Constraint Layout

<?xml version="1.0" encoding="utf-8"?>

<android.support.constraint.ConstraintLayout
        xmlns:android="<http://schemas.android.com/apk/res/android>"
        xmlns:tools="<http://schemas.android.com/tools>"
        xmlns:app="<http://schemas.android.com/apk/res-auto>"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity" 
        android:background="@color/screenBackground">
</android.support.constraint.ConstraintLayout>

Here is the code after adding the TextView for the hash and the button to initiate an origin chain

<TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="0"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintTop_toTopOf="parent" 
        android:textSize="12sp"
        app:layout_constraintVertical_bias="0.3"
        android:textColor="@android:color/white" 
        android:id="@+id/bwHashTextView"
        app:layout_constraintStart_toStartOf="parent"
        android:layout_marginEnd="32dp"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_marginRight="32dp" 
        android:layout_marginLeft="32dp"
        android:layout_marginStart="32dp"/>

<Button
        android:text="Create Origin"
        android:background="@color/buttonBackground"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/origin_button"
        app:layout_constraintStart_toEndOf="parent"
        android:layout_marginStart="8dp"
        app:layout_constraintEnd_toStartOf="parent"
        android:layout_marginEnd="8dp" 
        android:layout_marginTop="8dp"
        app:layout_constraintTop_toBottomOf="@+id/bwHashTextView" 
        android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toBottomOf="parent"/>

Note

marginStart is the same as marginLeft and marginEnd is the same as marginRight

You can bring in your own font with the TextView - app:fontFamily selector

You can create the button through code or through using the design editor by dragging in a Button from the Common or Buttons Palette

Our First Activity

Once you have the layout set, let's get to creating an origin chain in our simple app.

Set up auto imports

Before we begin, we need to make sure we set up auto imports so Android Studio automatically imports any classes that are needed by the Kotlin code.

To do this (in Android Studio)

  1. Click on file
  2. Go to other settings
  3. Then go to preferences for new projects
  4. Then go to click on other settings
  5. Then go to auto import
  6. Finally, click Add Unambiguous Imports on the fly

This will reduce the work you'll have to do on your end as your simple app needs to include more dependencies.

Start with Creating a Bound Witness

We will work in the kotlin class MainAcitivity.kt which is the activity for our screen.

To start we want to create a function to create and sign an origin chain

private fun originChainCreator() : XyoOriginChainCreator {

}

Why is this private? We only need the mainActivities function that the user initiates with the button tap to be public. This is good practice.

Set up the values needed for origin chain

This will get us ready to get the bound witness so that we can create an origin chain

private fun originChainCreator() : XyoOriginChainCreator {
    val storage = XyoInMemoryStorageProvider()
    val hasher = XyoBasicHashBase.createHashType(XyoSchemas.SHA_256, "SHA-256")
    val blockRepo = XyoStorageOriginBlockRepository(storage, hasher)
    val stateRepo = XyoStorageOriginStateRepository(storage)
    // a slightt rename for the spcific return that we want. This can be whatever you like
    val creator = XyoOriginChainCreator(blockRepo, stateRepo, hasher)
}

Set up the listener

It's time to add a listener for bound witness to our creator, without a bound witness we can't have an origin chain. This addListener takes two arguments, a key, and a callback for the listener

We bring in a function that will confirm the successful boundwitness and use that bound witness object to get the byte to hex string info that we want to display

creator.addListener("main", object: XyoNodeListener() {
    override fun onBoundWitnessEndSuccess(boundWitness: XyoBoundWitness) {
    super.onBoundWitnessEndSuccess(boundWitness)
    
  }
})

In order for us to successfully display an origin chain hash each time we tap the button, we want to avoid blocking any current threads. For this we use the GlobalScope launch extension function. This is a coroutine, if you are familiar with Kotlin then you have probably worked with coroutines before. If not, here is some reading that you can do.

In this function we get our hash from the boundWitness that we listened for.

    GlobalScope.launch {
    val hash = boundWitness.getHash(hasher).await().bytesCopy.toHexString()
    
    }

Now to avoid any delays or asynchronous behavior we want to provide the app with an ability to queue up UI actions should the current thread not be UI related. For this we will use the runOnUiThread method in our GlobalScope coroutine

  runOnUIThread {
    bwHashTextView.text = hash
  }

Here we are using setting the bwHashTextView.text to the hash when the UI is ready for it. You should recognize the bwHashTextView from the activity_main.xml file.

private fun originChainCreator() : XyoOriginChainCreator {
        val storage = XyoInMemoryStorageProvider()
        val hasher = XyoBasicHashBase.createHashType(XyoSchemas.SHA_256, "SHA-256")
        val blockRepo = XyoStorageOriginBlockRepository(storage, hasher)
        val stateRepo = XyoStorageOriginStateRepository(storage)
        val creator = XyoOriginChainCreator(blockRepo, stateRepo, hasher)

        creator.addListener("main", object: XyoNodeListener() {
            override fun onBoundWitnessEndSuccess(boundWitness: XyoBoundWitness) {
                super.onBoundWitnessEndSuccess(boundWitness)

                GlobalScope.launch {
                    val hash = boundWitness.getHash(hasher).await().bytesCopy.toHexString()

                runOnUiThread {
                  bwHashTextView.text = hash
              }
          }
      }
  })
}

We use the core sdk to create a signer, add the signer to the origin state, and return the origin chain

  val signer = XyoSha256WithSecp256K.newInstance()

  creator.originState.addSigner(signer)

  return creator

Our final originChainCreator() should look like this

    private fun originChainCreator() : XyoOriginChainCreator {
        val storage = XyoInMemoryStorageProvider()
        val hasher = XyoBasicHashBase.createHashType(XyoSchemas.SHA_256, "SHA-256")
        val blockRepo = XyoStorageOriginBlockRepository(storage, hasher)
        val stateRepo = XyoStorageOriginStateRepository(storage)
        val creator = XyoOriginChainCreator(blockRepo, stateRepo, hasher)

        creator.addListener("main", object: XyoNodeListener() {
            override fun onBoundWitnessEndSuccess(boundWitness: XyoBoundWitness) {
                super.onBoundWitnessEndSuccess(boundWitness)

                GlobalScope.launch {
                    val hash = boundWitness.getHash(hasher).await().bytesCopy.toHexString()

                    runOnUiThread {
                        bwHashTextView.text = hash
                    }
                }
            }
        })

        val signer = XyoSha256WithSecp256K.newInstance()

        creator.originState.addSigner(signer)

        return creator
    }

Now we have a chain that we can assign to our node for the create method tied to our button tap. Since we have included GlobalScope and runOnUiThread to our addListener function, we should have no collisons.

We add the created node as a local variable in our MainActivity class

// the node representing our chain for the user
var node = originChainCreator()

This function is what creates our content view with the current state.

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
  }

Now we only need to add an setOnClickListener for our button. We could add an onClick selector in our xml, but this is a preferred practice.

// use the id from the button

origin_button.setOnClickListener {
  // again to avoid blockages
  GlobalScope.launch {
    node.selfSignOriginChain().await()
  }
}

We have now set up the node to sign off and display the bound witness hash after tapping the Origin Chain button.

Here is the complete MainActivity class

class MainActivity : AppCompatActivity() {
    var node = originChainCreator()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        origin_button.setOnClickListener {
            GlobalScope.launch {
                node.selfSignOriginChain().await()
            }
        }
    }

    private fun originChainCreator() : XyoOriginChainCreator {
        val storage = XyoInMemoryStorageProvider()
        val hasher = XyoBasicHashBase.createHashType(XyoSchemas.SHA_256, "SHA-256")
        val blockRepo = XyoStorageOriginBlockRepository(storage, hasher)
        val stateRepo = XyoStorageOriginStateRepository(storage)
        val creator = XyoOriginChainCreator(blockRepo, stateRepo, hasher)

        creator.addListener("main", object: XyoNodeListener() {
            override fun onBoundWitnessEndSuccess(boundWitness: XyoBoundWitness) {
                super.onBoundWitnessEndSuccess(boundWitness)

                GlobalScope.launch {
                    val hash = boundWitness.getHash(hasher).await().bytesCopy.toHexString()

                    runOnUiThread {
                        bwHashTextView.text = hash
                    }
                }
            }
        })

        val signer = XyoSha256WithSecp256K.newInstance()

        creator.originState.addSigner(signer)

        return creator
    }
}

Run the project

We have our interactivity set and our layout set. We can now click on the run button.

The run button is on the upper right hand of the Android Studio interface, it is a play button next to the edit configurations menu and the build hammer button.

Once you click on the play button, it will build the application, and if not installed already install the application on your connected Android device or your chosen emulator.

You should now see the app appear similar to your layout from the design viewer.

location layout

Test the functionality by tapping on create origin, when you tap the button you should see a hash appear above in the textArea.

app with gps and origin hash

Go ahead and tap the button again for a new hash.

Congratulations you have now integrated the XYO SDK Core into your Android application.

Add Location

Let's keep going. We want to add a heuristic and see what heuristic we are adding. We'll add a GPS location to our bound witness chain.

Let's add another <TextView> to the main activity xml

activity_main.xml

    <TextView
            android:id="@+id/textViewLatLng"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:layout_marginLeft="8dp"
            android:layout_marginEnd="8dp"
            android:layout_marginRight="8dp"
            android:layout_marginBottom="8dp"
            android:text="@string/_0"
            android:textColor="@android:color/white"
            android:textSize="18sp"
            app:fontFamily="@font/lato_bold"
            app:layout_constraintBottom_toTopOf="@+id/origin_button"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/bwHashTextView" />

We set the constraints to ensure that the gps location heuristic that we are adding is between the Create Origin button and the hash text view.

Double check the app layout. This layout is viewable in the latest android studio. This should be to the right of the text editor in the preview. If not, you can click preview on the right navigation under Gradle.

We should be good with our views and button. Now let's add a location.

Get permission

Before we add a location heuristic we are going to need permission from the user to access the location on a smartphone. We can also use this best practice if we are working on a device simulator.

Since this is a simple application we should not spend too much time or code on permissions (if you are working to integrate XYO into a production ready app, make sure to have a more robust permission handler than what is presented here)

This is based on the requestPermissions method from the ActivityCompat class for activity features.

This will check permissions before the sample app runs for the first time. This will go in the onCreate() method.

val permissions = arrayOf(android.Manifest.permission.ACCESS_FINE_LOCATION)

ActivityCompat.requestPermissions(this, permissions, 0)

We also need to update the android manifest xml file with the permission:

    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

This permission element should be in the root and not in the <application> element.

Here is what the permission dialog will look like

location permission

Your manifest should look like this:

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="com.example.sampleapplication">

    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

    <application
            android:allowBackup="true"
            android:icon="@mipmap/ic_launcher"
            android:label="@string/app_name"
            android:roundIcon="@mipmap/ic_launcher_round"
            android:supportsRtl="true"
            android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>

                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>

        <meta-data
                android:name="preloaded_fonts"
                android:resource="@array/preloaded_fonts"/>
    </application>

</manifest>

So, we have cleared the permissions hurdle, now let's add the location heuristic.

Again in our main readme, you should see an example of adding a heuristic that looks like this:

This is a pseudo code for what we need to add a heuristic

node.addHeuristic("MyHeuristic", object : XyoHeuristicGetter {
    // will get called right before the bound witness starts
    override fun getHeuristic(): XyoBuff? {
        if (conditionIsMet()) {
            // object will be put into the bound witness
                return getMyHeuristic()
        }

        // object will not be put into the bound witness 
        return null
    }
})

What we want to do is add the heuristic to the node in the OnCreate() method, this heuristic will be added right before the chain is signed.

node.addHeuristic("GPS", <someHeuristicResolver>)

Let's get the heuristic to add

// the gpsHeuristicResolver is what will be plugged in to the addHeuristic method
    private val gpsHeuristicResolver = object : XyoHeuristicGetter {

        override fun getHeuristic(): XyoIterableStructure? {
            // bring in the location manager
            val locationManager = applicationContext.getSystemService(Context.LOCATION_SERVICE) as LocationManager
            // check if we have permission
            if (ContextCompat.checkSelfPermission(applicationContext, android.Manifest.permission.ACCESS_FINE_LOCATION)
                == PackageManager.PERMISSION_GRANTED) {
                // with permission we get the last known location from the location manager
                val lastLocation = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER)

                if (lastLocation != null) {
                    // as long as we have a location, we take it and convert it for inclusion in the Origin Chain
                    val encodedLat = ByteBuffer.allocate(8).putDouble(lastLocation.latitude).array()
                    val encodedLng = ByteBuffer.allocate(8).putDouble(lastLocation.longitude).array()
                    val lat = XyoObjectStructure.newInstance(XyoSchemas.LAT, encodedLat)
                    val lng = XyoObjectStructure.newInstance(XyoSchemas.LNG, encodedLng)
                    // let the user see the GPS in a readable format
                    runOnUiThread {
                        textViewLatLng.text = lastLocation.latitude.toString() + ", " + lastLocation.longitude.toString()
                    }

                    return XyoIterableStructure.createUntypedIterableObject(XyoSchemas.GPS, arrayOf(lat, lng))
                }
                // if we don't have permission
            } else {
                runOnUiThread {
                    textViewLatLng.text = "no gps permission"
                }
            }
            return null
        }
    }
}

Here we check that we have the permission to get the location, and if we have the permission, we get the last known location if there is one, then we encode the location coordinates before we create a new XyoObjectStructure for the heuristic to be compatible with our origin chain object.

We also add a runOnUiThread to print out the non-encoded location coordinates so that the user can see a human readable version of the location that is added to the origin chain.

We also added another text response if the permission was not obtained no gps permission

Once we have the resolver set, we can plug it into the addHeuristic method

override fun onCreate(savedInstanceState: Bundle?) {
  ...
  node.addHeuristic("GPS", gpsHeuristicResolver)
}

The onCreate() method should look like this when we are done

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)

        val permissions = arrayOf(android.Manifest.permission.ACCESS_FINE_LOCATION)
        ActivityCompat.requestPermissions(this, permissions,0)

        node.addHeuristic("GPS", gpsHeuristicResolver)

        origin_button.setOnClickListener {
            GlobalScope.launch {
                node.selfSignOriginChain().await()
            }
        }
    }

Now rebuild and run the app.

When you tap or click (in a simulator) the create origin button, you should see the GPS coordinate appear right before the hash.

app with gps and origin hash

Conclusion

You have now created an origin chain and added the gps heuristic to the origin chain.

Made with 🔥and ❄️ by XY - The Persistent Company

Last updated on 8/26/2019
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