MAUI - Android Auto - How To

[development-jantar]

1 Modify AndroidManifest - In the tag add support for Android Auto

<!-- Support for Android Auto -->
<!-- Knowledge - https://issuetracker.google.com/issues/363903527 -->
<!-- Knowledge - https://github.com/annikensyvertsen/AutomotiveExample?tab=readme-ov-file -->
<!-- Knowledge - https://developer.android.com/training/cars/apps/iot -->
<!-- Knowledge - https://developer.android.com/training/cars#supported-app-categories -->
<!-- Knowledge - https://issuetracker.google.com/issues/363903527 -->
<meta-data android:name="com.google.android.gms.car.application" android:resource="@xml/automotive_app" />
<!-- Knowledge - https://developer.android.com/reference/kotlin/androidx/car/app/versioning/CarAppApiLevels -->
<!-- Knowledge - https://developer.android.com/jetpack/androidx/releases/car-app -->
<meta-data android:name="androidx.car.app.minCarApiLevel" android:value="1" />
	

2 Add automotive_app.xml in Platforms/Android/Resources/xml

<?xml version="1.0" encoding="utf-8"?>
<automotiveApp>
	<!-- What kind of application is this? -->
	<!-- Knowledge - https://github.com/mikelor/Chaaos -->
	<uses name="template" />
</automotiveApp>

3 Add AndroidAutoReceiver.cs in Platforms/Android/Auto

// This code was generated by CoPilot based on link bellow.
// Knowledge - https://stackoverflow.com/questions/39320048/how-to-detect-if-phone-is-connected-to-android-auto
using global::Android.Content;
using global::Android.Database;

namespace Maui.Platforms.Android.Auto
{
    public class AndroidAutoConnectionDetector(global::Android.Content.Context context) : global::Android.Content.BroadcastReceiver
    {
        // Constants
        const string CAR_CONNECTION_STATE = "CarConnectionState";
        const string ACTION_CAR_CONNECTION_UPDATED = "androidx.car.app.connection.action.CAR_CONNECTION_UPDATED";
        const int CONNECTION_TYPE_PROJECTION = 2;
        const string CAR_CONNECTION_AUTHORITY = "androidx.car.app.connection";

        // Use global::Android.Net.Uri so we do not get namespace conflict
        static global::Android.Net.Uri? PROJECTION_HOST_URI;

        // Get car context
        private readonly global::Android.Content.Context _context = context;
        public event Action<bool>? ConnectionChanged;

        // Start listening
        public void Start()
        {
            _context.RegisterReceiver
            (
                this,
                new IntentFilter(ACTION_CAR_CONNECTION_UPDATED),
                global::Android.Content.ReceiverFlags.Exported
            );

            QueryForState();
        }

        // Stop listening
        public void Stop()
        {
            _context.UnregisterReceiver(this);
        }

        // New status update
        public override void OnReceive(global::Android.Content.Context? context, global::Android.Content.Intent? intent)
        {
            QueryForState();
        }

        // Read the state and update connection status
        private void QueryForState()
        {
            try
            {
                // Is this defined?
                PROJECTION_HOST_URI ??= new global::Android.Net.Uri.Builder()?.Scheme("content")?.Authority(CAR_CONNECTION_AUTHORITY)?.Build(); 

                // Do we have all the parameters needed for reading the status?
                if (_context is not null && _context.ContentResolver is not null && PROJECTION_HOST_URI is not null) 
                {
                    using ICursor? cursor = _context.ContentResolver.Query(
                        PROJECTION_HOST_URI,
                        [CAR_CONNECTION_STATE],
                        null,
                        null,
                        null
                    );

                    if (cursor != null && cursor.MoveToFirst())
                    {
                        int colIndex = cursor.GetColumnIndex(CAR_CONNECTION_STATE);
                        if (colIndex >= 0)
                        {
                            int state = cursor.GetInt(colIndex);
                            bool connected = state == CONNECTION_TYPE_PROJECTION;

                            ConnectionChanged?.Invoke(connected);
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                //LogError("QueryForState - AndroidAuto - failed.", false, ex);
            }
        }
    }
}

which you use in MainActivity.cs

private AndroidAutoConnectionDetector? _detector;
protected override void OnCreate(Bundle? savedInstanceState)
{
    base.OnCreate(savedInstanceState);

    // Listen for events - is car screen connected or not
    _detector = new AndroidAutoConnectionDetector(global::Android.App.Application.Context);
    _detector.ConnectionChanged += connected =>
    {
        // IsCarScreenConnected = connected; - optional, save to variable

        // The screen is connected, we can load the data if the the app is in the background
        if (connected)
        {
            WeakReferenceMessenger.Default.Send(new AppResumed(true));
        }

        // Refresh screen, new data
        WeakReferenceMessenger.Default.Send(new CarReloadDataMessage(true));
    };
    _detector.Start();
}

4 Add Sessions/CarSession.cs in Platforms/Android/Auto/Sessions

using Android.Content;
using AndroidX.Car.App;
using Maui.Platforms.Android.Auto.Screens;

namespace Maui.Platforms.Android.Auto.Sessions
{
    public class CarSession : Session
    {
        public override Screen OnCreateScreen(Intent? intent)
        {
            return new MainScreen(CarContext);
        }
    }
}

5 Add CarService.cs in Platforms/Android/Auto/Services

using Android.App;
using AndroidX.Car.App;
using AndroidX.Car.App.Validation;
using Maui.Platforms.Android.Auto.Sessions;

namespace Maui.Platforms.Android.Auto.Services
{
    // Knowledge - https://developer.android.com/training/cars/apps/iot - we create XML
    [Service(Exported = true)]

    // Service - https://developer.android.com/training/cars#supported-app-categories
    // Service - https://developer.android.com/training/cars/apps/iot
    [IntentFilter(["androidx.car.app.CarAppService"], Categories = new[] { "androidx.car.app.category.IOT" })]

    public class CarService : CarAppService
    {
        public override HostValidator CreateHostValidator()
        {
            return HostValidator.AllowAllHostsValidator;
        }

        public override Session OnCreateSession()
        {
            // Log the event - optional
            // Log("Android Auto session was created.");

            return new CarSession();
        }
    }
}

6 Add MainScreen.cs in Platforms/Android/Auto/Screens

using AndroidX.Car.App;
using AndroidX.Car.App.Model;
using CommunityToolkit.Mvvm.Messaging;
using Plugin.Maui.Audio;
using Action = AndroidX.Car.App.Model.Action;

namespace Maui.Platforms.Android.Auto.Screens;

public class MainScreen : Screen
{
    // We need this to refresh controls
    private readonly IDispatcherTimer? _reloadTimeoutTimer;
    private bool dataReload = false;

    // On button click, we play the specific sound - user feedback
    private static AsyncAudioPlayer? audioPlayer = null;
    public static AsyncAudioPlayer? AudioPlayer
    {
        get => audioPlayer;
        set => audioPlayer = value;
    }

    private static System.IO.Stream? audioStream = null;
    public static System.IO.Stream? AudioStream
    {
        get => audioStream;
        set => audioStream = value;
    }

    public MainScreen(CarContext carContext) : base(carContext)
    {
        WeakReferenceMessenger.Default.Unregister<CarReloadDataMessage>(this);
        WeakReferenceMessenger.Default.Register<CarReloadDataMessage>(this, (recipient, message) =>
        {
            dataReload = true;
        });

        // Is timer already in place?
        if (_reloadTimeoutTimer != null)
        {
            // Smo uspešni,
            _reloadTimeoutTimer?.Stop();
            _reloadTimeoutTimer = null;
        }

        // Start new timer
        _reloadTimeoutTimer = Dispatcher.GetForCurrentThread()?.CreateTimer();
        if (_reloadTimeoutTimer != null)
        {
            _reloadTimeoutTimer.Interval = TimeSpan.FromMilliseconds(500);
            _reloadTimeoutTimer.Tick += (s, e) =>
            {
                // If this updates too often, it does not work
				// So we check if we need to reload data or not on every timer run
                if (dataReload)
                {
                    // There is also option to invalidate current template, which would run the event for rerendering
                    // Knowledge - https://github.com/felipebaltazar/Maui.Auto.Car/blob/7972f71315fba6fc0ad4c7c7099627155a701b0e/Maui.Auto.Car/Platforms/Android/Services/AndroidAutoService.cs#L30 with CoPilot generating the code
                    
					// When the command is fired, we wait for new data reload
					// We want the customer to see the button spinning
                    if (ScreenManager is not null && ScreenManager.ScreenStack is not null && ScreenManager.ScreenStack.Count > 0 && ScreenManager.Top is GridTemplateScreen mainScreen && mainScreen.isCommandInProgress == false)
                    {
                        App.SafeInvokeOnMainThread(this, () =>
                        {
                            ScreenManager.Pop();
                        });

                        dataReload = false;
                    }
                }
            };

            _reloadTimeoutTimer.IsRepeating = true;
            _reloadTimeoutTimer.Start();
        }

        // We can notify the car screen is connected - optional
        // IsCarScreenConnected = true;
    }

    public override ITemplate OnGetTemplate()
    {
        // If there is no screen, add GridScreen
        // With this, we make sure the first screen for the customer is already the Grid (1 click less)
        // Thank you CoPilot algorithm
        if (ScreenManager?.Top is not GridTemplateScreen)
        {
            // It can happen the screen is not available any more
            // Napaka - Accessed the car host after it became invalidated
            try
            {
                ScreenManager?.Push(new GridTemplateScreen(CarContext));
            }
            catch (Exception ex)
            {
                //LogError("Unable to render OnGetTemplate on Android Auto", false, ex);
            }
        }

        // Return the template from the Top Screen Manager
        if (ScreenManager is not null && ScreenManager.Top is not null)
        {
            return ScreenManager.Top.OnGetTemplate();
        }

        // Errors?
        var gridItemListBuilder = new ItemList.Builder();
        gridItemListBuilder.SetNoItemsMessage("No controls are available. Open the App and check your data.");

		// Create empty Grid List
        var gridItemList = gridItemListBuilder.Build();

        // Return empty Grid Template
        return new GridTemplate.Builder()
                   .SetTitle("Loading Android Auto failed")
                   .SetHeaderAction(Action.Back)
                   .SetSingleList(gridItemList)
                   .Build();   
   }
}

7 Add GridTemplateScreen.cs in Platforms/Android/Auto/Screens

using AndroidX.Car.App;
using AndroidX.Car.App.Model;
using AndroidX.Core.Graphics.Drawable;
using Platforms.Android.Auto.OnClickListeners;
using System.Reflection;
using Action = AndroidX.Car.App.Model.Action;

namespace Platforms.Android.Auto.Screens
{
    public class GridTemplateScreen(CarContext carContext) : Screen(carContext)
    {
        // We need this for screen refresh
        static private readonly SemaphoreSlim _semaphoreSlimAndroidAutoReloadData = new(1, 1);
        public bool isCommandInProgress = false;
        static private string safeTitleText = string.Empty;

        public override ITemplate OnGetTemplate()
        {
            // We can get mupltiple reload events
			// If the operation is in place and we do not get green ligth in 50ms, skip
			// We will wait for next data reload event
			// Prevent long waiting line of processes
            if (_semaphoreSlimAndroidAutoReloadData.Wait(500 + 50))
            {
                try
                {
                    // The screen is connected - optional
                    // IsCarScreenConnected = true;

					// Maybe there will be no controls
                    var gridItemListBuilder = new ItemList.Builder();
                    gridItemListBuilder.SetNoItemsMessage("No controls are available. Open the App and check your data.");

                    // Get all controls - your custom data
                    foreach (Control control in AllControls)
                    {
                        if (control.IsDisabled == false)
                        {
                            // Get the icon from the control
                            // Otherwise, get the app icon
                            // We can not dynamically set the image
                            // Java.Lang.IllegalStateException Message=When a grid item is loading, the image must not be set and vice versa
                            int? resourceId = GetDrawableResourceId(control.ImageLayoutControl);
                            IconCompat? iconCompat;
                            if (resourceId is not null)
                            {
                                iconCompat = IconCompat.CreateWithResource(CarContext, resourceId.Value);
                            }
                            else
                            {
                                iconCompat = IconCompat.CreateWithResource(CarContext, Microsoft.Maui.Resource.Mipmap.appicon);
                            }

                            // Set default setting for the Grid Button
                            GridItem.Builder gridItemBuilder = new GridItem.Builder()
                            .SetTitle(control.DeviceName)
                            .SetText("")
                            .SetLoading(control.IsInLoadingState); // Spinner - feedback for the user

                            // Do we have the image or not?
                            // If the control is in loading state, do not set the image
                            // java.lang.IllegalStateException: When a grid item is loading, the image must not be set and vice versa
                            if (iconCompat is not null && !control.IsInLoadingState)
                            {
                                CarIcon? carIcon = new CarIcon.Builder(iconCompat).Build();
                                if (carIcon is not null)
                                {
                                    gridItemBuilder?.SetImage(carIcon);
                                }
                            }

                            // If the control is in loading state, do not set the click event
                            // java.lang.IllegalStateException: The click listener must not be set on the grid item when it is loading
                            if (!control.IsInLoadingState)
                            {
                                gridItemBuilder?.SetOnClickListener(new ActionOnClickListener(CarContext, control, this));
                            }

                            // Create a list of grid buttons
                            // Dereference of a possibly null reference.
                            if (gridItemBuilder is not null)
                            {
                                GridItem gridItem = gridItemBuilder.Build();

                                // Add to the Grid list
                                gridItemListBuilder.AddItem(gridItem);
                            }                            
                        }
                    }

                    // We have the control - Android Grid Button List
                    var gridItemList = gridItemListBuilder.Build();

                    // Driver distraction optimization - testing, can not confirm if it influences on distractionOptimized
                    safeTitleText = "Your custom status - what is happening in the app";
                    safeTitleText = safeTitleText.Length > 120 ? safeTitleText[..120] : safeTitleText;

                    // Create GridTemplate
                    // We use title for the operatin status - customer knows what is happening
                    return new GridTemplate.Builder()
                        .SetTitle(safeTitleText)
                        .SetHeaderAction(Action.AppIcon)
                        .SetSingleList(gridItemList)
                        .Build();
                }
                catch (Exception ex)
                {
                    // LogError("Reloading Android Auto view failed");
  
                    // Error!:)
                    var gridItemListBuilder = new ItemList.Builder();
                    gridItemListBuilder.SetNoItemsMessage("No controls are available for Google Auto.");

                    // Create empty list with error title
                    var gridItemList = gridItemListBuilder.Build();

                    // Return empty grid template
                    return new GridTemplate.Builder()
                               .SetTitle("Loading Android Auto failed")
                               .SetHeaderAction(Action.Back)
                               .SetSingleList(gridItemList)
                               .Build();
                }
                finally
                {
                    _semaphoreSlimAndroidAutoReloadData.Release();
                }
            }

            // Distraction optimized restrictions
            safeTitleText = "Your custom status - what is happening in the app";
            safeTitleText = safeTitleText.Length > 120 ? safeTitleText[..120] : safeTitleText;

            // Error - return empty grid template
            return new GridTemplate.Builder()
                       .SetTitle(safeTitleText)
                       .SetHeaderAction(Action.Back)
                       .Build();
        }

        // Thank you CoPilot algorithm, think deep :)
        public static int? GetDrawableResourceId(string imageFilename)
        {
            if (string.IsNullOrWhiteSpace(imageFilename))
            {
                return null;
            }

            // Transform "something.png" to "something"
            string resourceName = Path.GetFileNameWithoutExtension(imageFilename).ToLowerInvariant();
	
			// Get the resource Id from the image name
            // This is auto generated class from Maui
            // Pictures are connected to specific int, public static int something => 21111230906;
            var resourceType = typeof(Microsoft.Maui.Resource.Drawable);

            // Get the map value
            PropertyInfo? field = resourceType.GetProperty(resourceName);
            if (field is not null)
            {
                // Get the value
                object? fieldValue = field.GetValue(null);
                if (fieldValue is int resourceId)
                {
                    return resourceId;
                }
            }

            return null;
        }
    }
}

8 Add GridTemplateScreen.cs in Platforms/Android/Auto/OnClickListeners

// I do not think this is in use anymore, it would be if we would have deeper navigation
using AndroidX.Car.App;
using AndroidX.Car.App.Model;
using Platforms.Android.Auto.Screens;

namespace Maui.Platforms.Android.Auto.OnClickListeners
{
    public class NavigationOnClickListener(CarContext carContext, ScreenManager screenManager) : Java.Lang.Object, IOnClickListener
    {
        private readonly CarContext mCarContext = carContext;
        private readonly ScreenManager mScreenManager = screenManager;

        void IOnClickListener.OnClick()
        {
            mScreenManager.Push(new GridTemplateScreen(mCarContext));
        }
    }
}

9 Add ActionOnClickListener.cs in Platforms/Android/Auto/ActionOnClickListener

using Android.Media;
using Android.Runtime;
using AndroidX.Car.App;
using AndroidX.Car.App.Model;
using CommunityToolkit.Mvvm.Messaging;
using Maui.Platforms.Android.Auto.Screens;
using Plugin.Maui.Audio;

namespace Maui.Platforms.Android.Auto.OnClickListeners;

public class ActionOnClickListener(CarContext? carContext, Control item, GridTemplateScreen gridTemplateScreen) : Java.Lang.Object, IOnClickListener
{
    private readonly CarContext? _carContext = carContext;
    private readonly Control _item = item; // this is your custom data
    private readonly GridTemplateScreen _gridTemplateScreen = gridTemplateScreen;

    public async void OnClick()
    {
        // Prevent user clicking on the button if the operation is already in place
        if (_item.IsInLoadingState)
        {
            return;
        }

        // If the process is not done in one second, make the button available again
        IDispatcherTimer? _androidAutoButtonPressedTimer = Dispatcher.GetForCurrentThread()?.CreateTimer();
        if (_androidAutoButtonPressedTimer != null)
        {
            _androidAutoButtonPressedTimer.Interval = TimeSpan.FromMilliseconds(1000);
            _androidAutoButtonPressedTimer.Tick += (s, e) =>
            {
                _gridTemplateScreen.isCommandInProgress = false;
                _item.IsInLoadingState = false;

                // Refresh the screen
                WeakReferenceMessenger.Default.Send(new CarReloadDataMessage(true));
            };
            _androidAutoButtonPressedTimer.IsRepeating = false;
            _androidAutoButtonPressedTimer.Start();
        }

        // Operation is in place
        _gridTemplateScreen.isCommandInProgress = true;
        _item.IsInLoadingState = true;

        App.SafeInvokeOnMainThread(this, () => 
        {
            // This is all made up from CoPilot algorithm
			// This update the screen - user feedback - button is in loading state - spinning image
            if (_carContext is not null)
            {
                ScreenManager? screenManager = _carContext.GetCarService(Java.Lang.Class.FromType(typeof(AndroidX.Car.App.ScreenManager))).JavaCast<AndroidX.Car.App.ScreenManager>();
                screenManager?.Pop();                
            }            
        });

        // Knowledge - https://github.com/jfversluis/Plugin.Maui.Audio
        // We read the file once - optimization
		// This part is not working well yet - problems with not silencing other music or button sound is not played
        if (MainScreen.AudioStream is null)
        {
            // Knowledge https://github.com/jfversluis/Plugin.Maui.Audio/blob/main/docs/audio-player.md#configure-the-playback-options
            // Knowledge - https://developer.android.com/reference/android/media/AudioAttributes
            // Knowledge - https://developer.android.com/reference/android/media/AudioAttributes#CONTENT_TYPE_SONIFICATION
            AudioPlayerOptions audioPlayerOptions = new()
            {
            #if ANDROID
                AudioUsageKind = AudioUsageKind.Notification,
                AudioContentType = AudioContentType.Sonification
            #endif
            };

            MainScreen.AudioStream = await FileSystem.OpenAppPackageFileAsync("beeep.mp3");
            MainScreen.AudioPlayer = Plugin.Maui.Audio.AudioManager.Current.CreateAsyncPlayer(MainScreen.AudioStream, audioPlayerOptions);
        }

        // Play the sound
        if (MainScreen.AudioPlayer is not null)
        {
            await App.SafeInvokeOnMainThreadAsync(this, async () =>
            {
                await MainScreen.AudioPlayer.PlayAsync(CancellationToken.None);
            });
        }

        // Do smt here, open the door?
    }
}

[development-jantar]

Example for one control:

Spinning effect:

Testing:

Install Android Studio

• https://developer.android.com/studio
• Android Studio, open settings, find Android SDK
• 1x SDK Platform
• 1x Android SDK Build-Tools 36
• 1x Android Auto API Simulators
• 1x Android Auto Desktop Head Unit Emulator
• 1x Android Emulator
• 1x Android SDK Platform-Tools
• 1x Google USB Driver

Open adb
Visual Studio, click Open Android Adb Command Prompt
Run the cmd prompt: adb forward tcp:5277 tcp:5277
(also take care of the adb path for later step, if this will not work by default)

Run Desktop head unit
cd C:\Users\default\AppData\Local\Android\Sdk\extras\google\auto
desktop-head-unit.exe

it should say:
[I]: Connecting over ADB to localhost:5277...
[I]: connected

Not working?
If it does not work, edit you headunit.ini. settings in, exmaple: C:\Users\default.android\headunit.ini.
Add adbPath=Whole-path-to-adb.exe (adb path - above)

Run the Android Auto on mobile phone

• Enable Developer options
• Open the Android Auto app
• Additional settings in the app
• click on the "..." on the right upper corner
• click "Start head unit server"

Open the App on your phone, the screen should blink and the app should show in the Android Auto.

For more information, check this discussion topic, where all the resources where shared.

Sharing the knowledge on behalf of Codeks Smart House App, Jantar.

[development-jantar]

Current problem is "Unavailable, for your safety. This activity is not available while driving.". Although we followed the steps described and tested many other solutions found online, the app was approved by Google for Android Auto but still does not work while driving. Any help would be appreciated.

[development-jantar]

Maybe this is related - https://issuetracker.google.com/issues/449779015 , while the message is different: "This task can't be completed while driving".

I can accomplish this while runing emulator "AppData\Local\Android\Sdk\extras\google\auto>desktop-head-unit.exe" and typing restrict all.