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Android SDK Tutorial (Pre-release)

{:.no_toc}

This tutorial is written for readers who are new to either or both Blockstack and Android to create a decentralized application. It contains the following content:

TOC {:toc}

This tutorial was extensively tested using Android Studio 3.1 on a MacBook Air running High Sierra 10.13.4. If your environment is different, you may encounter slight or even major discrepancies when performing the procedures in this tutorial. Please join the Blockstack community Slack and post questions or comments to the #support channel.

Finally, this tutorial is written for all levels from the beginner to the most experienced. For best results, beginners should follow the guide as written. It is expected that the fast or furiously brilliant will skip ahead and improvise on this material at will. Fair journey one and all.

If you prefer, you can skip working through the tutorial all together. Instead, you can download the final project code and import it into Android Studio to review it.

Understand the sample application flow

When complete, the sample application is a simple hello-world display. It is intended for user on an Android phone.

Only users with an existing blockstack.id can run your final sample application. When complete, users interact with the sample application by doing the following:

Set up your environment

This sample application has two code bases, a Blockstack hello-blockstack application and a hello-andriod Android application. Before you start developing the sample, there are a few elements you need in your environment.

Install Android Studio

If you are an experienced Android developer and already have an Android development environment on your workstation, you can use that and skip this step. However, you will need to adjust the remaining instructions for your environment.

Follow the installation instructions to download and Android Studio 3.1 for your operating system. Depending on your network connection, this can take between 15-30 minutes.

Do you have npm?

The Blockstack code in this tutorial relies on the npm dependency manager. Before you begin, verify you have installed npm using the which command to verify.

$ which npm
/usr/local/bin/npm

If you don't find npm in your system, install it.

Install the Blockstack test rig

Users interact with Blockstack-enabled applications through a web browser. You can Blockstack in test mode, on localhost or you can interact with completed apps through the Blockstack webapp which is available at [https://browser.blockstack.org/].

If you have already installed Blockstack for testing locally and have an existing Blockstack ID, skip this section. Otherwise, continue onto install Blockstack.

Go to Blockstack
Install the version appropriate for your operating system.

Use npm to install Yeoman and the Blockstack App Generator

You use npm to install Yeoman. Yeoman is a generic scaffolding system that helps users rapidly start new projects and streamline the maintenance of existing projects.

Install Yeoman.
```
npm install -g yo
```
Install the Blockstack application generator.
```
npm install -g generator-blockstack
```

Build the Blockstack hello-world

In this section, you build a Blockstack hello-world application. Then, you modify the hello-world to interact with the Android app via a redirect.

Generate and launch your hello-blockstack application

In this section, you build an initial React.js application called hello-blockstack.

Create a hello-blockstack directory.
```
mkdir hello-blockstack
```
Change into your new directory.
```
cd hello-blockstack
```

Use Yeoman and the Blockstack application generator to create your initial hello-blockstack application.

yo blockstack:react

You should see several interactive prompts.

$ yo blockstack:react
==========================================================================
We are constantly looking for ways to make yo better!
May we anonymously report usage statistics to improve the tool over time?
More info: https://github.com/yeoman/insight & http://yeoman.io
========================================================================== No

     _-----_     ╭──────────────────────────╮
    |       |    │      Welcome to the      │
    |--(o)--|    │      Blockstack app      │
    ---------    │        generator!        │
    ( _U_ )      ╰──────────────────────────╯
    /___A___\   /
     |  ~  |
   __'.___.'__
        |°  Y

? Are you ready to build a Blockstack app in React? (Y/n)

Respond to the prompts to populate the initial app.

After the process completes successfully, you see a prompt similar to the following:

[fsevents] Success:
"/Users/theuser/repos/hello-blockstack/node_modules/fsevents/lib/binding/Release/node-v59-darwin-x64/fse.node"
is installed via remote npm notice created a lockfile as package-lock.json.
You should commit this file. added 1060 packages in 26.901s

Run the initial application.

$ npm start

> hello-blockstack@0.0.0 start /Users/moxiegirl/repos/hello-blockstack
> webpack-dev-server

Project is running at http://localhost:8080/
webpack output is served from /
404s will fallback to /index.html
Hash: 4d2312ba236a4b95dc3a
Version: webpack 2.7.0
Time: 2969ms
                                 Asset       Size  Chunks                    Chunk Names
....
  Child html-webpack-plugin for "index.html":
     chunk    {0} index.html 541 kB [entry] [rendered]
         [0] ./~/lodash/lodash.js 540 kB {0} [built]
         [1] ./~/html-webpack-plugin/lib/loader.js!./src/index.html 533 bytes {0} [built]
         [2] (webpack)/buildin/global.js 509 bytes {0} [built]
         [3] (webpack)/buildin/module.js 517 bytes {0} [built]
 webpack: Compiled successfully.

The system opens a browser displaying your running application.

At this point, the browser is running a Blockstack server on your local host. This is for testing your applications only.

Choose Sign in with Blockstack

The system displays a prompt allowing you to create a new Blockstack ID or restore an existing one.
Follow the prompts appropriate to your situation.

If you are restoring an existing ID, you may see a prompt about your user being nameless, ignore it. At this point you have only a single application on your test server. So, you should see this single application, with your own blockstack.id display name, once you are signed in:

Add a redirect end point to your application

When a user opens the webapp from the Blockstack Browser on an Android phone, you want the web app to redirect the user to your Android application. The work you do here will allow it.

From the terminal command line, change directory to the root of your sample application directory.
Use the touch command to add a redirect endpoint to your application.

This endpoint on the web version of your app will redirect Android users back to your mobile app.
```
$ touch public/redirect.html
```
Open redirect.html and add code to the endpoint.
```
<!DOCTYPE html>
<html>
<head>
  <title>Hello, Blockstack!</title>
  <script>
  function getParameterByName(name) {
    var match = RegExp('[?&]' + name + '=([^&]*)').exec(window.location.search);
    return match && decodeURIComponent(match[1].replace(/\+/g, ' '));
  }

  var authResponse = getParameterByName('authResponse')
  window.location="myblockstackapp:" + authResponse
  </script>
<body>
</body>
</html>
```
Blockstack apps are identified by their domain names. The endpoint will receive a get request with the query parameter authResponse=XXXX and should redirect the browser to myblockstackapp:XXXX.

myblockstackapp: is custom protocol handler. The handler should be unique to your application. Your app's web-based authentication uses this handler to redirect the user back to your Android app. Later, you'll add a reference to this handler in your Android application.
Close and save the redirect.html file.
Ensure your Blockstack compiles successfully.

Create the hello-android project

In this section, you'll create an Android application in Android Studio. You'll run the application in the emulator to test it.

Create a simple project

In this section, you create an inital project. You'll validate the application's iniatial state by creating an emulator to run it in. Open Android Studio and do the following:

Open Android Studio and choose Start a new Andriod Studio project.

If studio is already started, choose File > New > New Project.

Enter these fields in the Create Android Project page.

Application Name	`hello-android`
Company domain	`USERNAME.example.com`
Project location	`/Users/USERNAME/AndroidStudioProjects/helloandroid`
Include Kotlin support	Set (checked)

Press Next to display Target Android Devices.
Check Phone and Tablet.
Choose API 27: Andriod 8.1 (Oreo) for the target version.
Press Next.
Choose Empty Activity and press Next.
Leave the Configure Activity dialog with its defaults.
Press Finish.

Android studio builds your initial project. This can take a bit the first time you do it.

Run the app in an emulator

In this section, you run the appliation and create an emulator when prompted.

Once the project is imported into studio, click the app module in the Project window.
Then, select Run > Run (or click the green arrow in the toolbar).

Studio prompts you to Select Deployment Target.
Choose Create New Virtual Device and press OK.

Studio prompts you to Select Hardware.
Choose a Phone running Pixel XL.

Studio prompts you for a system image.
Choose Oreo which is API level 27 and press Next.

Studio asks you to verify your new emulator configuration.
Press Finish.

The emulation takes a moment to build. Then, studio launches the emulation and opens your application.

Configure your application with the Blockstack SDK

Now that you have created your initial project and verified it running in an emulator, you are ready to begin configuring the application for use with Blockstack.

In studio, open the AndroidManifest.xml file.

Add an <intent-filter> with the custom handler for Blockstack.

<intent-filter>
  <action android:name="android.intent.action.VIEW" />
  <category android:name="android.intent.category.DEFAULT" />
  <category android:name="android.intent.category.BROWSABLE" />
  <data android:scheme="myblockstackapp" />
 </intent-filter>

Open the Project's build.gradle file.

Add the Jitpack repository maven { url 'https://jitpack.io' } to the repositories section.

When you finish, that section looks like this:

allprojects {
  repositories {
      google()
      jcenter()
      maven { url 'https://jitpack.io' }
  }
}

Open the Module build.gradle file.

Set the defaultConfig minSdkVersion to 19.

When you are done, you should see (within your own username not moxiegirl):

android {
    compileSdkVersion 27
        defaultConfig {
            applicationId "com.example.moxiegirl.hello_android"
            minSdkVersion 19
            targetSdkVersion 27
            versionCode 1
            versionName "1.0"
            testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        }
   ...
}

Below this, add the Blockstack Android SDK dependency to your project's dependencies list:

When you are done you should see:

dependencies {
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'com.android.support:appcompat-v7:27.1.1'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.android.support:design:27.1.1'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    implementation 'com.github.blockstack:blockstack-android:0.4.0'
}

NOTE: Ignore the warning on the appcompat` dependencies.

Sync your project.

Be sure to check the sync completed successfully.
Run your app in the emulator.

You've made a lot of changes, make sure the emulator is still running correctly.

Add a simple interface

Open the app/res/layout/activity_main.xml file.

The activity_main.xml file defines the graphical elements. Some elements are required before you can functionality to your MainActivity.kt code.

Replace the entire content of the file with the following code:

The new interface includes a BlockstackSignInButton which is provided by the SDK. This SDK includes a themed "Sign in with Blockstack" button (BlockstackSignInButton). You use this button here with the org.blockstack.android.sdk.ui.BlockstackSignInButton class.

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<org.blockstack.android.sdk.ui.BlockstackSignInButton
    android:id="@+id/signInButton"
    android:layout_width="307dp"
    android:layout_height="45dp"
    android:layout_margin="4dp"
    android:layout_marginEnd="185dp"
    android:layout_marginStart="39dp"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    tools:layout_editor_absoluteY="16dp" />

<TextView
    android:id="@+id/userDataTextView"
    android:layout_width="370dp"
    android:layout_height="27dp"
    tools:layout_editor_absoluteX="6dp"
    tools:layout_editor_absoluteY="70dp" />

</android>

This codes adds a button and some text to your application.

Choose Run > Apply changes.
Choose Run > Run app in the emulator.

The emulator now contains a new interface with a button:

Add session & authentication code

Open the MainActivity.kt file.

Add some additional imports to the top below the android.os.Bundle import.

When you are done, your imports should appear as follows:

import android.content.Intent
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.view.View
import kotlinx.android.synthetic.main.activity_main.*
import org.blockstack.android.sdk.BlockstackSession
import org.blockstack.android.sdk.Scope
import org.blockstack.android.sdk.UserData
import org.blockstack.android.sdk.toBlockstackConfig

Add a variable for the Blockstack session before onCreate.

class MainActivity : AppCompatActivity() {

    private var _blockstackSession: BlockstackSession? = null

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

Replace the existing the onCreate function with the following:

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

    val scopes = arrayOf(Scope.StoreWrite)
    val config = "https://flamboyant-darwin-d11c17.netlify.com"
                    .toBlockstackConfig(scopes)

    _blockstackSession = BlockstackSession(this, config)

    signInButton.isEnabled = true                

    signInButton.setOnClickListener { view: View ->
        blockstackSession().redirectUserToSignIn {
           // only called on error
      }
    }
    if (intent?.action == Intent.ACTION_VIEW) {
        // handle the redirect from sign in
        handleAuthResponse(intent)
    }
}

This new onCreate does several things:

Define the initial state for the signInButton.
Supply authentication information for connecting to your Blockstack app: appDomain and scopes (for redirectURI, manifestURI the default values are used)
Add a listener for the button click.

Notice that the application in this example is a URI you have not set up. Registering and application name takes time, so in time's interest you'll use an existing app that is identical to the hello-world you created earlier. For a production version, you'll need to replace appDomain, redirectURI, manifestURI and scopes with values appropriate for your app.

Add a private function to reflect when a user successfully signs in.

private fun onSignIn(userData: UserData) {
        userDataTextView.text = "Signed in as ${userData.decentralizedID}"
        signInButton.isEnabled = false
}

Handle sign in requests with an onNewIntent function if the activity was already opened when signing in

Retrieve the authentication token from the custom protocol handler call and send it to the Blockstack session.
```
override fun onNewIntent(intent: Intent?) {
  super.onNewIntent(intent)

  if (intent?.action == Intent.ACTION_VIEW) {
      handleAuthResponse(intent)
  }
}
```

Create a handler for the authentication response.

private fun handleAuthResponse(intent: Intent) {
   val response = intent.dataString
   if (response != null) {
       val authResponseTokens = response.split(':')

       if (authResponseTokens.size > 1) {
           val authResponse = authResponseTokens[1]

           blockstackSession().handlePendingSignIn(authResponse, { userData ->
               if (userData.hasValue) {
                  // The user is now signed in!
                  runOnUiThread {
                     onSignIn(userData.value!!)
                  }
               }
           })
       }
   }
}

Add the convenience method to access the blockstack session.

fun blockstackSession() : BlockstackSession {
  val session = _blockstackSession
   if(session != null) {
      return session
   } else {
    throw IllegalStateException("No session.")
  }
}

Verify your final MainActivity.kt code looks like this:

class MainActivity : AppCompatActivity() {

    private var _blockstackSession: BlockstackSession? = null

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

        signInButton.isEnabled = false

        val scopes = arrayOf(Scope.StoreWrite)
        val config = "https://flamboyant-darwin-d11c17.netlify.com"
                    .toBlockstackConfig(scopes)

        _blockstackSession = BlockstackSession(this, config)
        signInButton.isEnabled = true                    

        signInButton.setOnClickListener { view: View ->
            blockstackSession().redirectUserToSignIn { 
               // only called on error
            }
        }
        if (intent?.action == Intent.ACTION_VIEW) {
            handleAuthResponse(intent)
        }
    }

    private fun onSignIn(userData: UserData) {
        userDataTextView.text = "Signed in as ${userData.decentralizedID}"

        signInButton.isEnabled = false
    }

    override fun onNewIntent(intent: Intent?) {
        super.onNewIntent(intent)

        if (intent?.action == Intent.ACTION_VIEW) {
            handleAuthResponse(intent)
        }
    }

    private fun handleAuthResponse(intent: Intent) {
        val response = intent.dataString
        if (response != null) {
            val authResponseTokens = response.split(':')

            if (authResponseTokens.size > 1) {
                val authResponse = authResponseTokens[1]

                blockstackSession().handlePendingSignIn(authResponse, { userData ->
                    if (userData.hasValue) {
                        // The user is now signed in!
                        runOnUiThread {
                            onSignIn(userData.value!!)
                        }
                    }
                })
            }
        }
    }

    fun blockstackSession() : BlockstackSession {
        val session = _blockstackSession
        if(session != null) {
            return session
        } else {
            throw IllegalStateException("No session.")
        }
    }
}

Run the final app in the emulator

Choose Run > Apply changes.
Choose Run > Run app in the emulator.
When you see the application open, choose Sign in with Blockstack.

The system prompts you how to open.
Choose Chrome and click ALWAYS.
Move through the rest of the Chrome prompts.

The system presents you with your final application.
Work through the Blockstack prompts to login.

Where to go next

Congratulations, you've completed your Android app using the new, pre-release Blockstack Android SDK. Thank you for trying this pre-release. Please let us know about your experience by tweeting to @blockstack.

Learn more about Blockstack by trying another tutorial.

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