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How to Code a Navigation Drawer for an Android App

  • What You'll Be Creating

    The material design team at Google defines the functionality of a navigation drawer in Android as follows:

    The navigation drawer slides in from the left and contains the navigation destinations for your app.

    An example of a popular Android app that implements the navigation drawer is the Inbox app from Google, which uses a navigation drawer to navigate to different sections of the application. You can check it yourself by downloading the Inbox app from the Google Play store, if you don't already have it on your device. The screenshot below shows Inbox with the navigation drawer pulled open.

    The user can view the navigation drawer when they swipe a finger from the left edge of the activity. They can also find it from the home activity (the top level of the app), by tapping the app icon (also known as the "hamburger" menu) in the action bar. 

    Note that if you have many different destinations (more than six, say) in your app, it's recommended that you use a navigation drawer. 

    In this post, you'll learn how to display navigation items inside a navigation drawer in Android. We'll cover how to use the DrawerLayout and NavigationView API to perform this task. For a bonus, you'll also learn how to use the Android Studio templates feature to quickly bootstrap your project with a navigation drawer. 

    A sample project (in Kotlin) for this tutorial can be found on our GitHub repo so you can easily follow along.


    To be able to follow this tutorial, you'll need:

    1. Create an Android Studio Project

    Fire up Android Studio and create a new project (you can name it NavigationDrawerDemo) with an empty activity called MainActivity. Make sure to also check the Include Kotlin support check box. 

    2. Adding the DrawerLayout and NavigationView

    To begin using DrawerLayout and NavigationView in your project, you'll need to import the design support and also the Android support artifact. So add these to your module's build.gradle file to import them. 

    dependencies { implementation '' implementation '' }

    Also, include both the DrawerLayout widget and also the NavigationView widget in your res/layout/activlty_main.xml file.

    <?xml version="1.0" encoding="utf-8"?> < xmlns:android="" xmlns:app="" xmlns:tools="" android:id="@+id/drawer_layout" android:layout_width="match_parent" android:layout_height="match_parent" tools:openDrawer="start"> <include layout="@layout/app_bar_main" android:layout_width="match_parent" android:layout_height="match_parent" /> < android:id="@+id/nav_view" android:layout_width="wrap_content" android:layout_height="match_parent" android:layout_gravity="start" app:headerLayout="@layout/nav_header_main" app:menu="@menu/activity_main_drawer" /> </>

    Here we created a DrawerLayout widget with the id drawer_layout. The tools:openDrawer property is used to display the navigation drawer when the XML layout is open in Android Studio design view. 

    The official documentation says the following about DrawerLayout:

    DrawerLayout acts as a top-level container for window content that allows for interactive "drawer" views to be pulled out from one or both vertical edges of the window.

    After adding the DrawerLayout widget, we included a child layout which points to @layout/app_bar_main. 

    Here is my app_bar_main.xml resource file. This file simply has a CoordinatorLayout, an AppBarLayout, and a Toolbar widget. 

    <?xml version="1.0" encoding="utf-8"?> < xmlns:android="" xmlns:app="" xmlns:tools="" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity"> < android:layout_width="match_parent" android:layout_height="wrap_content" android:fitsSystemWindows="true" android:theme="@style/AppTheme.AppBarOverlay"> < android:id="@+id/toolbar_main" android:layout_width="match_parent" android:layout_height="?attr/actionBarSize" android:background="?attr/colorPrimary" app:layout_scrollFlags="scroll|enterAlways" app:popupTheme="@style/AppTheme.PopupOverlay" /> </> </>

    Finally, we created a NavigationView widget. The official documentation says the following about NavigationView:

    NavigationView represents a standard navigation menu for application. The menu contents can be populated by a menu resource file.

    In the NavigationView XML widget, you can see that we added an android:layout_gravity attribute with value start. This is used to position the drawer—you want the drawer to come out from left or right (the start or end on platform versions that support layout direction). In our own case, the drawer will come out from the left. 

    We also included an app:headerLayout attribute which points to @layout/nav_header_main. This will add a View as a header of the navigation menu.

    Here is my nav_header_main.xml layout resource file:

    <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="" android:id="@+id/nav_header" android:layout_width="match_parent" android:layout_height="160dp" android:background="@color/colorAccent" android:clickable="true" android:focusable="true" android:foreground="?attr/selectableItemBackgroundBorderless" android:gravity="bottom" android:orientation="vertical" android:padding="16dp" android:theme="@style/ThemeOverlay.AppCompat.Dark"> <ImageView android:id="@+id/nav_header_imageView" android:layout_width="64dp" android:layout_height="64dp" android:src="@mipmap/ic_launcher" /> <TextView android:id="@+id/nav_header_textView" android:layout_width="match_parent" android:layout_height="wrap_content" android:paddingTop="16dp" android:text="Chike Mgbemena" android:textAppearance="@style/TextAppearance.AppCompat.Body1" /> </LinearLayout>

    This layout file simply has a LinearLayout, an ImageView, and a TextView. 

    To include the menu items for the navigation drawer, we can use the attribute app:menu with a value that points to a menu resource file. 

    < app:menu="@menu/activity_main_drawer" />

    Here is the res/menu/activity_main_drawer.xml menu resource file:

    <?xml version="1.0" encoding="utf-8"?> <menu xmlns:android=""> <group> <item android:id="@+id/nav_item_one" android:icon="@drawable/ic_drafts_black_24dp" android:title="Item 1" /> <item android:id="@+id/nav_item_two" android:icon="@drawable/ic_drafts_black_24dp" android:title="Item 2" /> <item android:id="@+id/nav_item_three" android:icon="@drawable/ic_drafts_black_24dp" android:title="Item 3" /> </group> <group android:id="@+id/group_menu"> <item android:id="@+id/nav_item_four" android:title="Item 4" /> <item android:id="@+id/nav_item_five" android:title="Item 5" /> </group> <item android:title="Title 1"> <menu> <item android:id="@+id/nav_item_six" android:icon="@drawable/ic_drafts_black_24dp" android:title="Item 6" /> <item android:id="@+id/nav_item_seven" android:icon="@drawable/ic_drafts_black_24dp" android:title="Item 7" /> </menu> </item> </menu>

    Here we have defined a Menu using the <menu> which serves as a container for menu items. An <item> creates a MenuItem, which represents a single item in a menu.

    We then defined our first menu group using the <group>. A <group> serves as an invisible container for <item> elements—menu items in our case. Each of the <item> elements has an id, an icon, and a title. Note that a horizontal line will be drawn at the end of each <group> for us when shown in the navigation drawer. 

    A <item> can also contain a nested <menu> element in order to create a submenu—we did just this in our last <item>. Notice that this last <item> has a title property. 

    Note that when showing the navigation list items from a menu resource, we could use a ListView instead. But, by configuring the navigation drawer with a menu resource, we get the material design styling on the navigation drawer for free! If you used a ListView, you would have to maintain the list and also style it to meet the recommended material design specs for the navigation drawer

    3. Initialization of Components

    Next, we are going to initialize instances of our DrawerLayout and ActionBarDrawerToggle. Initialization is going to happen inside onCreate() in MainActivity.kt.

    import android.content.res.Configuration import android.os.Bundle import import import import import android.view.MenuItem class MainActivity : AppCompatActivity() { private lateinit var drawer: DrawerLayout private lateinit var toggle: ActionBarDrawerToggle override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) val toolbar: Toolbar = findViewById( setSupportActionBar(toolbar) drawer = findViewById( toggle = ActionBarDrawerToggle(this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close) drawer.addDrawerListener(toggle) supportActionBar?.setDisplayHomeAsUpEnabled(true) supportActionBar?.setHomeButtonEnabled(true) } // ... }

    The ActionBarDrawerToggle sets up the app icon located on the left of the action bar or toolbar to open and close the navigation drawer. To be able to create an instance of ActionBarDrawerToggle, we have to provide the following parameters: 

    • a parent context—for example, in an Activity you use this, while in a Fragment you call getActivity()
    • an instance of the DrawerLayout widget to link to the activity's ActionBar
    • the icon to place on top of the app icon to indicate that there is a toggle
    • the string resources for the open and close operations respectively (for accessibility)

    We invoked the method addDrawerListener() on a DrawerLayout so as to connect an ActionBarDrawerToggle with a DrawerLayout. 

    Note that we also enable the app icon via setHomeButtonEnabled() and enable it for “up” navigation via setDisplayHomeAsUpEnabled(). 

    We then forward the onPostCreate(), onConfigurationChanged(), and onOptionsItemSelected() activity callback methods on to the toggle:

    class MainActivity : AppCompatActivity() { // ... override fun onPostCreate(savedInstanceState: Bundle?) { super.onPostCreate(savedInstanceState) toggle.syncState() } override fun onConfigurationChanged(newConfig: Configuration?) { super.onConfigurationChanged(newConfig) toggle.onConfigurationChanged(newConfig) } override fun onOptionsItemSelected(item: MenuItem?): Boolean { if (toggle.onOptionsItemSelected(item)) { return true } return super.onOptionsItemSelected(item) } }

    Here is what the syncState() does, according to the official documentation

    Synchronizes the state of the drawer indicator/affordance with the linked DrawerLayout... This should be called from your Activity's onPostCreate method to synchronize after the DrawerLayout's instance state has been restored, and any other time when the state may have diverged in such a way that the ActionBarDrawerToggle was not notified. (For example, if you stop forwarding appropriate drawer events for a period of time.) 4. Testing the App

    At this point, we can run the app!

    As you can see, launching the app will show the “hamburger” navigation drawer icon in the action bar. Try tapping this app icon to open the drawer. Also, clicking on the navigation drawer items won't do anything—we're going to handle that part in the next section. 

    5. Handling Click Events

    Now, let's see how to handle click events for each of the items in the navigation drawer. Note that clicking on any item is supposed to take you to a new Activity or Fragment—that's why it's called a navigation drawer!

    First, your activity needs to implement the NavigationView.OnNavigationItemSelectedListener. 

    class MainActivity : AppCompatActivity(), NavigationView.OnNavigationItemSelectedListener { // ... }

    By implementing this contract or interface, we must now override the only method: onNavigationItemSelected(). 

    class MainActivity : AppCompatActivity(), NavigationView.OnNavigationItemSelectedListener { // ... override fun onNavigationItemSelected(item: MenuItem): Boolean { when (item.itemId) { -> Toast.makeText(this, "Clicked item one", Toast.LENGTH_SHORT).show() -> Toast.makeText(this, "Clicked item two", Toast.LENGTH_SHORT).show() -> Toast.makeText(this, "Clicked item three", Toast.LENGTH_SHORT).show() -> Toast.makeText(this, "Clicked item four", Toast.LENGTH_SHORT).show() } return true } }

    This method is invoked when an item in the navigation menu is selected. We used the when expression to perform different actions based on the menu item that was clicked—the menu item ids serve as constants for the when expression. 

    Next, we have to initialize our NavigationView and set this listener inside onCreate() of our activity. 

    class MainActivity : AppCompatActivity(), NavigationView.OnNavigationItemSelectedListener { // ... override fun onCreate(savedInstanceState: Bundle?) { // ... val navigationView: NavigationView = findViewById( navigationView.setNavigationItemSelectedListener(this) // ... } // ...

    Run the project again!

    When you click on some items, a toast message is displayed—just what we expected. But remember that clicking on an item should take the user to a new Activity or Fragment (we ignored this here for brevity's sake). 

    You will notice that when you click on an item, the drawer still remains. It would be better if it closed automatically anytime an item was clicked. Let's see how to do that. 

    override fun onNavigationItemSelected(item: MenuItem): Boolean { when (item.itemId) { -> Toast.makeText(this, "Clicked item one", Toast.LENGTH_SHORT).show() -> Toast.makeText(this, "Clicked item two", Toast.LENGTH_SHORT).show() -> Toast.makeText(this, "Clicked item three", Toast.LENGTH_SHORT).show() -> Toast.makeText(this, "Clicked item four", Toast.LENGTH_SHORT).show() } drawer.closeDrawer(GravityCompat.START) return true }

    To close the drawer after a link has been clicked, simply invoke closeDrawer() on an instance of DrawerLayout and pass GravityCompat.START to the method. 

    Run the project one more time and see the result! 

    6. Handling the Back Button Being Pressed

    When the drawer is open, it would be a better user experience not to close the home activity if the Back button is pressed. This is the way popular apps like Google's Inbox app work. 

    So, when the drawer is open and the Back button is pressed, only close the drawer instead of the current home activity. Then, if the user presses the Back button again, the home activity should be closed. 

    Here's how we can achieve this: 

    override fun onBackPressed() { if (drawer.isDrawerOpen(GravityCompat.START)) { drawer.closeDrawer(GravityCompat.START) } else { super.onBackPressed() } }

    Run the project again and test it out! 

    7. Bonus: Using Android Studio Templates

    Now that you have learnt about the APIs involved to create a navigation drawer, I'll show you a shortcut that will make it faster next time. You can simply use a template instead of coding a navigation drawer Activity from scratch. 

    Android Studio provides code templates that follow the Android design and development best practices. These existing code templates (available in Java and Kotlin) can help you quickly kick-start your project. One such template can be used to create a navigation drawer activity. 

    I'll show you how to use this handy feature in Android Studio. 

    For a new project, fire up Android Studio. 

    Enter the application name and click the Next button. 

    You can leave the defaults as they are in the Target Android Devices dialog. Click the Next button again. 

    In the Add an Activity to Mobile dialog, scroll down and select Navigation Drawer Activity. Click the Next button after that. 

    In the last dialog, you can rename the Activity name, layout name or title if you want. Finally, click the Finish button to accept all configurations. 

    Android Studio has now helped us to create a project with a navigation drawer activity. Really cool!

    You are strongly advised to explore the code generated. 

    You can use templates for an already existing Android Studio project too. Simply go to File > New > Activity > Navigation Drawer Activity.  

    The templates that come included with Android Studio are good for simple layouts and making basic apps, but if you want to kick-start your app even further, you might consider some of the app templates available from Envato Market

    They’re a huge time saver for experienced developers, helping them to cut through the slog of creating an app from scratch and focus their talents instead on the unique and customised parts of creating a new app.


    In this tutorial, you learned how to create a navigation drawer in Android using the DrawerLayout and NavigationView API from scratch. We also explored how to easily and quickly use the Android Studio templates to create a navigation drawer. 

    I highly recommend checking out the official material design guidelines for navigation drawers to learn more about how to properly design and use navigation drawers in Android.   

    To learn more about coding for Android, check out some of our other courses and tutorials here on Envato Tuts+!

    3 days 21 hours ago

Android Things: Adding Google Assistant

  • With the growth of the Internet of Things (IoT), developers and engineers have had to rethink how users interact with devices on a day-to-day basis. 

    While screens work well for websites and most apps, devices that interface with the real world can be a bit more tedious to operate if you have to use multiple buttons or a screen in order to function. One of the ways around this is to enable voice controls on your devices. 

    In this tutorial you will learn about Google Assistant and how you can add it to your Android Things IoT devices.

    If you need a little background on Android Things before you start, check out some of my other posts here on Envato Tuts+.

    Assistant SDK

    The Google Assistant SDK allows you to add voice controls with key word detection, natural language processing, and other machine learning features to your IoT devices. There's a lot that can be done with the Assistant SDK, but this tutorial will just focus on the basics: how you can include it on your Android Things devices in order to ask questions, get information, and interact with standard "out of the box" Assistant functionality.

    As far as hardware requirements, you have a few options. You can use a Raspberry Pi flashed with Android Things with an AIY Voice Kit.

    Or you can use a standard speaker with AUX connector and a USB microphone.

    Additionally, you can use any other I²S hardware configuration. While we won't discuss I²S in detail in this tutorial, it's worth noting that the Voice Kit will use this protocol. Once you have a microphone and speaker set up, you will also need to add a button to your device. This button will need to keep track of two states: pressed and released. You can accomplish this with a multi-pronged arcade button, or a standard button with a pull-down resistor attached to one of the poles.


    Once you have hooked up your hardware, it's time to add the Assistant SDK to your device. First, you will need to create a new credentials file for your device. You can find the instructions for this in the Google Assistant docs. Once you have your credentials.json file, you will need to place it into the res/raw directory of your Android Things module.

    After your credentials are created with Google, you will need to declare some permissions for your app. Open the AndroidManifest.xml file and add the following lines within the manifest tag, but before the application tag.

    <uses-permission android:name="android.permission.RECORD_AUDIO" /> <uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS" /> <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="" />

    It's worth noting that you will need to restart your device after installing the app with these permissions in order for them to be granted.

    Next you will need to copy the gRPC module into your app for communicating with the home device. This gets a little tricky, so the best place to get it is from the Google Assistant Android Things sample app, which can be found in the Android Things GitHub account. You will then need to update your settings.gradle file to reflect the new module.

    include ':mobile', ':things', ':grpc'

    After updating settings.gradle, include the module as a dependency in your things module by including the following line in the things module's build.gradle file and include Google's button driver (you will need this for activating the microphone) and optional Voice Hat driver if you are using that hardware.

    compile project(':grpc') compile '' //optional compile ''

    You'll also need to include protobuf as a dependency in your project-level build.gradle file.

    classpath ""

    Next, let's include the oauth2 library in our project by opening the things module's build.gradle file and adding the following under the dependencies node:

    compile('') { exclude group: 'org.apache.httpcomponents', module: 'httpclient' }

    You may run into conflicts here if your project has the Espresso dependency, with an error message similar to this:

    Warning:Conflict with dependency '' in project ':things'. Resolved versions for app (1.3.9) and test app (2.0.1) differ. See for details.

    If so, just remove the Espresso dependency from build.gradle.

    After you have synced your project, create a new class named to access your credentials.

    public class Credentials { static UserCredentials fromResource(Context context, int resourceId) throws IOException, JSONException { InputStream is = context.getResources().openRawResource(resourceId); byte[] bytes = new byte[is.available()];; JSONObject json = new JSONObject(new String(bytes, "UTF-8")); return new UserCredentials(json.getString("client_id"), json.getString("client_secret"), json.getString("refresh_token") ); } } }Embedded Assistant Helper Class

    Once your class is created, it's time to create a new class named This is a helper class that was originally written by engineers at Google to easily wrap the Google Assistant for Android Things. While this class is fairly straightforward to use by just including it into your project, we will want to dive into it and understand how it actually works. 

    The first thing you will do is create two inner abstract classes that will be used for handling callbacks in the conversation and requests to the Assistant API.

    public class EmbeddedAssistant { public static abstract class RequestCallback { public void onRequestStart() {} public void onAudioRecording() {} public void onSpeechRecognition(String utterance) {} } public static abstract class ConversationCallback { public void onResponseStarted() {} public void onResponseFinished() {} public void onConversationEvent(EventType eventType) {} public void onAudioSample(ByteBuffer audioSample) {} public void onConversationError(Status error) {} public void onError(Throwable throwable) {} public void onVolumeChanged(int percentage) {} public void onConversationFinished() {} } }

    Once your two inner classes are written, go ahead and define the following set of global values at the top of your class. The majority of these will be initialized later in this file. These values are used to keep track of device state and interactions with the Assistant API.

    private static final String ASSISTANT_API_ENDPOINT = ""; private static final int AUDIO_RECORD_BLOCK_SIZE = 1024; private RequestCallback mRequestCallback; private ConversationCallback mConversationCallback; //Used for push-to-talk functionality private ByteString mConversationState; private AudioInConfig mAudioInConfig; private AudioOutConfig mAudioOutConfig; private AudioTrack mAudioTrack; private AudioRecord mAudioRecord; private int mVolume = 100; // Default to maximum volume. private UserCredentials mUserCredentials; private MicrophoneMode mMicrophoneMode; private HandlerThread mAssistantThread; private Handler mAssistantHandler; // gRPC client and stream observers. private int mAudioOutSize; // Tracks the size of audio responses to determine when it ends. private EmbeddedAssistantGrpc.EmbeddedAssistantStub mAssistantService; private StreamObserver<ConverseRequest> mAssistantRequestObserver; Handling API Responses

    While the above has a StreamObserver<ConverseRequest> object for requests to the Assistant API, you will also need one for responses. This object will consist of a switch statement that checks the state of the response and then handles it accordingly.

    private StreamObserver<ConverseResponse> mAssistantResponseObserver = new StreamObserver<ConverseResponse>() { @Override public void onNext(ConverseResponse value) { switch (value.getConverseResponseCase()) {

    The first case checks for the end of a user speaking and uses the ConversationCallback to let the rest of the class know that a response is imminent.

    case EVENT_TYPE: mConversationCallback.onConversationEvent(value.getEventType()); if (value.getEventType() == EventType.END_OF_UTTERANCE) { mConversationCallback.onResponseStarted(); } break;

    The next case will check and update conversation, volume, and microphone state.

    case RESULT: // Update state. mConversationState = value.getResult().getConversationState(); // Update volume. if (value.getResult().getVolumePercentage() != 0) { int volumePercentage = value.getResult().getVolumePercentage(); mVolume = volumePercentage; mAudioTrack.setVolume(AudioTrack.getMaxVolume() * volumePercentage / 100.0f); mConversationCallback.onVolumeChanged(volumePercentage); } if (value.getResult().getSpokenRequestText() != null && !value.getResult().getSpokenRequestText().isEmpty()) { mRequestCallback.onSpeechRecognition(value.getResult() .getSpokenRequestText()); } // Update microphone mode. mMicrophoneMode = value.getResult().getMicrophoneMode(); break;

    The third case will take an audio result and play it back for the user.

    case AUDIO_OUT: if (mAudioOutSize <= value.getAudioOut().getSerializedSize()) { mAudioOutSize = value.getAudioOut().getSerializedSize(); } else { mAudioOutSize = 0; onCompleted(); } final ByteBuffer audioData = ByteBuffer.wrap(value.getAudioOut().getAudioData().toByteArray()); mAudioTrack.write(audioData, audioData.remaining(), AudioTrack.WRITE_BLOCKING); mConversationCallback.onAudioSample(audioData); break;

    The final case will simply forward errors that occurred during the conversation process.

    case ERROR: mConversationCallback.onConversationError(value.getError()); break;

    The final two methods within this stream handle error states and cleanup on completion of a conversation result.

    @Override public void onError(Throwable t) { mConversationCallback.onError(t); } @Override public void onCompleted() { mConversationCallback.onResponseFinished(); if (mMicrophoneMode == MicrophoneMode.DIALOG_FOLLOW_ON) { // Automatically start a new request startConversation(); } else { // The conversation is done mConversationCallback.onConversationFinished(); } }Streaming Audio

    Next, you will need to create a Runnable that will handle audio streaming on a different thread.

    private Runnable mStreamAssistantRequest = new Runnable() { @Override public void run() { ByteBuffer audioData = ByteBuffer.allocateDirect(AUDIO_RECORD_BLOCK_SIZE); int result =, audioData.capacity(), AudioRecord.READ_BLOCKING); if (result < 0) { return; } mRequestCallback.onAudioRecording(); mAssistantRequestObserver.onNext(ConverseRequest.newBuilder() .setAudioIn(ByteString.copyFrom(audioData)) .build());; } };Creating the Assistant

    Now that your global values are defined, it's time to go over the framework for creating the EmbeddedAssistant. You will need to be able to retrieve the credentials for your app using the class that was created earlier.

    public static UserCredentials generateCredentials(Context context, int resourceId) throws IOException, JSONException { return Credentials.fromResource(context, resourceId); }

    In order to instantiate itself, this class uses a private constructor and the builder pattern.

    private EmbeddedAssistant() {} public static class Builder { private EmbeddedAssistant mEmbeddedAssistant; private int mSampleRate; public Builder() { mEmbeddedAssistant = new EmbeddedAssistant(); }

    The Builder inner class contains multiple methods for initializing the values within the EmbeddedAssistant class, such as sample rate, volume, and user credentials. Once the build() method is called, all of the defined values will be set on the EmbeddedAssistant, global objects necessary for operation will be configured, and an error will be thrown if any necessary data is missing.

    public Builder setRequestCallback(RequestCallback requestCallback) { mEmbeddedAssistant.mRequestCallback = requestCallback; return this; } public Builder setConversationCallback(ConversationCallback responseCallback) { mEmbeddedAssistant.mConversationCallback = responseCallback; return this; } public Builder setCredentials(UserCredentials userCredentials) { mEmbeddedAssistant.mUserCredentials = userCredentials; return this; } public Builder setAudioSampleRate(int sampleRate) { mSampleRate = sampleRate; return this; } public Builder setAudioVolume(int volume) { mEmbeddedAssistant.mVolume = volume; return this; } public EmbeddedAssistant build() { if (mEmbeddedAssistant.mRequestCallback == null) { throw new NullPointerException("There must be a defined RequestCallback"); } if (mEmbeddedAssistant.mConversationCallback == null) { throw new NullPointerException("There must be a defined ConversationCallback"); } if (mEmbeddedAssistant.mUserCredentials == null) { throw new NullPointerException("There must be provided credentials"); } if (mSampleRate == 0) { throw new NullPointerException("There must be a defined sample rate"); } final int audioEncoding = AudioFormat.ENCODING_PCM_16BIT; // Construct audio configurations. mEmbeddedAssistant.mAudioInConfig = AudioInConfig.newBuilder() .setEncoding(AudioInConfig.Encoding.LINEAR16) .setSampleRateHertz(mSampleRate) .build(); mEmbeddedAssistant.mAudioOutConfig = AudioOutConfig.newBuilder() .setEncoding(AudioOutConfig.Encoding.LINEAR16) .setSampleRateHertz(mSampleRate) .setVolumePercentage(mEmbeddedAssistant.mVolume) .build(); // Construct AudioRecord & AudioTrack AudioFormat audioFormatOutputMono = new AudioFormat.Builder() .setChannelMask(AudioFormat.CHANNEL_OUT_MONO) .setEncoding(audioEncoding) .setSampleRate(mSampleRate) .build(); int outputBufferSize = AudioTrack.getMinBufferSize(audioFormatOutputMono.getSampleRate(), audioFormatOutputMono.getChannelMask(), audioFormatOutputMono.getEncoding()); mEmbeddedAssistant.mAudioTrack = new AudioTrack.Builder() .setAudioFormat(audioFormatOutputMono) .setBufferSizeInBytes(outputBufferSize) .build(); mEmbeddedAssistant.mAudioTrack.setVolume(mEmbeddedAssistant.mVolume * AudioTrack.getMaxVolume() / 100.0f);; AudioFormat audioFormatInputMono = new AudioFormat.Builder() .setChannelMask(AudioFormat.CHANNEL_IN_MONO) .setEncoding(audioEncoding) .setSampleRate(mSampleRate) .build(); int inputBufferSize = AudioRecord.getMinBufferSize(audioFormatInputMono.getSampleRate(), audioFormatInputMono.getChannelMask(), audioFormatInputMono.getEncoding()); mEmbeddedAssistant.mAudioRecord = new AudioRecord.Builder() .setAudioSource(AudioSource.VOICE_RECOGNITION) .setAudioFormat(audioFormatInputMono) .setBufferSizeInBytes(inputBufferSize) .build(); return mEmbeddedAssistant; } } Connecting to the Assistant API

    After the EmbeddedAssistant has been created, the connect() method will need to be called in order to connect to the Assistant API.

    public void connect() { mAssistantThread = new HandlerThread("assistantThread"); mAssistantThread.start(); mAssistantHandler = new Handler(mAssistantThread.getLooper()); ManagedChannel channel = ManagedChannelBuilder.forTarget(ASSISTANT_API_ENDPOINT).build(); mAssistantService = EmbeddedAssistantGrpc.newStub(channel) .withCallCredentials(MoreCallCredentials.from(mUserCredentials)); }

    After you have connected to the API, you will use two methods for starting and stopping conversations. These methods will post Runnable objects to mAssistantHandler in order to pass conversation state objects to the request and response streams.

    public void startConversation() { mAudioRecord.startRecording(); mRequestCallback.onRequestStart(); Runnable() { @Override public void run() { mAssistantRequestObserver = mAssistantService.converse(mAssistantResponseObserver); ConverseConfig.Builder converseConfigBuilder = ConverseConfig.newBuilder() .setAudioInConfig(mAudioInConfig) .setAudioOutConfig(mAudioOutConfig); if (mConversationState != null) { converseConfigBuilder.setConverseState(ConverseState.newBuilder() .setConversationState(mConversationState) .build()); } mAssistantRequestObserver.onNext( ConverseRequest.newBuilder() .setConfig( .build()); } });; } public void stopConversation() { Runnable() { @Override public void run() { mAssistantHandler.removeCallbacks(mStreamAssistantRequest); if (mAssistantRequestObserver != null) { mAssistantRequestObserver.onCompleted(); mAssistantRequestObserver = null; } } }); mAudioRecord.stop();; mConversationCallback.onConversationFinished(); }Shutting Down

    Finally, the destroy() method will be used for teardown when your app is closing and no longer needs to access the Assistant API.

    public void destroy() { Runnable() { @Override public void run() { mAssistantHandler.removeCallbacks(mStreamAssistantRequest); } }); mAssistantThread.quitSafely(); if (mAudioRecord != null) { mAudioRecord.stop(); mAudioRecord = null; } if (mAudioTrack != null) { mAudioTrack.stop(); mAudioTrack = null; } }Using the Assistant

    Once your helper classes are fleshed out, it's time to use them. You will do this by editing your Android Things MainActivity class to interact with the EmbeddedAssistant and hardware for controlling the Google Assistant. First, add the Button.OnButtonEventListener interface to your Activity.

    public class MainActivity extends Activity implements Button.OnButtonEventListener {

    Next you will need to add the member variables and constants that will be required by your app. These values will control the debounce of the button that triggers the Assistant, as well as the volume, the audio format, the UserCredentials class that you created earlier, and the hardware for your device.

    private static final int BUTTON_DEBOUNCE_DELAY_MS = 20; private static final String PREF_CURRENT_VOLUME = "current_volume"; private static final int SAMPLE_RATE = 16000; private static final int ENCODING = AudioFormat.ENCODING_PCM_16BIT; private static final int DEFAULT_VOLUME = 100; private int initialVolume = DEFAULT_VOLUME; private static final AudioFormat AUDIO_FORMAT_STEREO = new AudioFormat.Builder() .setChannelMask(AudioFormat.CHANNEL_IN_STEREO) .setEncoding(ENCODING) .setSampleRate(SAMPLE_RATE) .build(); // Hardware peripherals. private VoiceHat mVoiceHat; private Button mButton; private EmbeddedAssistant mEmbeddedAssistant; private UserCredentials userCredentials;

    Once you have your constants defined, you will need to create a few callback objects that will be used for conversations and requests with the assistant.

    private ConversationCallback mConversationCallback = new ConversationCallback() { @Override public void onConversationEvent(EventType eventType) {} @Override public void onAudioSample(ByteBuffer audioSample) {} @Override public void onConversationError(Status error) {} @Override public void onError(Throwable throwable) {} @Override public void onVolumeChanged(int percentage) { SharedPreferences.Editor editor = PreferenceManager .getDefaultSharedPreferences(AssistantActivity.this) .edit(); editor.putInt(PREF_CURRENT_VOLUME, percentage); editor.apply(); } @Override public void onConversationFinished() {} }; private RequestCallback mRequestCallback = new RequestCallback() { @Override public void onRequestStart() { //starting assistant request, enable microphones } @Override public void onSpeechRecognition(String utterance) {} };

    In mConversationCallback, you will notice that we save a volume change percentage in a shared preference. This allows your device volume to stay consistent for your users, even across reboots.

    As the assistant works asynchronously on your device, you will initialize everything for using the Assistant API in onCreate() by calling a set of helper methods that we will define over the rest of this tutorial.

    @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); initVoiceHat(); initButton(); initVolume(); initUserCredentials(); initEmbeddedAssistant(); }

    The first helper method is initVoiceHat(). If the Voice Hat shield is attached to a Raspberry Pi, this method will initialize the device so that users can use the attached microphone and speaker. If a Voice Hat is not attached, then a standard AUX speaker and USB microphone can be used and will be routed to automatically. The Voice Hat uses I2S to handle audio peripherals on the bus, and is wrapped by a driver class that was written by Google.

    private void initVoiceHat() { PeripheralManagerService pioService = new PeripheralManagerService(); List<String> i2sDevices = pioService.getI2sDeviceList(); if (i2sDevices.size() > 0) { try { mVoiceHat = new VoiceHat( BoardDefaults.getI2SDeviceForVoiceHat(), BoardDefaults.getGPIOForVoiceHatTrigger(), AUDIO_FORMAT_STEREO ); mVoiceHat.registerAudioInputDriver(); mVoiceHat.registerAudioOutputDriver(); } catch (IllegalStateException e) {} } }

    The assistant will only respond in this sample while a triggering button is held down. This button is initialized and configured like so:

    private void initButton() { try { mButton = new Button(BoardDefaults.getGPIOForButton(), Button.LogicState.PRESSED_WHEN_LOW); mButton.setDebounceDelay(BUTTON_DEBOUNCE_DELAY_MS); mButton.setOnButtonEventListener(this); } catch( IOException e ) {} }

    When the button is pressed, the assistant will start listening for a new conversation.

    @Override public void onButtonEvent(Button button, boolean pressed) { if (pressed) { mEmbeddedAssistant.startConversation(); } }

    You can find more information about GPIO and Android Things in my tutorial about input and output with Android Things.

    Since we stored volume information in our device's SharedPreferences, we can access it directly to initialize the device's volume.

    private void initVolume() { SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this); initialVolume = preferences.getInt(PREF_CURRENT_VOLUME, DEFAULT_VOLUME); }

    The Assistant SDK requires authentication for use. Luckily we created a method in the EmbeddedAssistant class earlier in this tutorial specifically for this situation.

    private void initUserCredentials() { userCredentials = null; try { userCredentials = EmbeddedAssistant.generateCredentials(this, R.raw.credentials); } catch (IOException | JSONException e) {} }

    The final helper method that was called in onCreate() will initialize the EmbeddedAssistant object and connect it to the API.

    private void initEmbeddedAssistant() { mEmbeddedAssistant = new EmbeddedAssistant.Builder() .setCredentials(userCredentials) .setAudioSampleRate(SAMPLE_RATE) .setAudioVolume(currentVolume) .setRequestCallback(mRequestCallback) .setConversationCallback(mConversationCallback) .build(); mEmbeddedAssistant.connect(); }

    The last thing that you will need to do is properly tear down your peripherals by updating the onDestroy() method in your Activity.

    @Override protected void onDestroy() { super.onDestroy(); if (mButton != null) { try { mButton.close(); } catch (IOException e) {} mButton = null; } if (mVoiceHat != null) { try { mVoiceHat.unregisterAudioOutputDriver(); mVoiceHat.unregisterAudioInputDriver(); mVoiceHat.close(); } catch (IOException e) {} mVoiceHat = null; } mEmbeddedAssistant.destroy(); }

    After all of this, you should be able to interact with your Android Things device as if it were a Google Home!


    In this tutorial, you learned about the Google Assistant and how it can be added to your Android Things applications. This feature gives your users a new way of interacting with and controlling your device, as well as access to the many features available from Google. This is only one part of the fantastic features that can go into an Android Things app and allow you to create new and amazing devices for your users.

    While you're here, check out some of my other posts on Android Things on Envato Tuts+!

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