# .NET MAUI - reporting events to the GUI In this page, we will send a notifiation of an event back to the .NET GUI. The resulting project is as follows: [ExcersisTapCallback.zip](/attachments/5) This way, we're completely disconnected with the Android stack and can focus on development in MAUI or .NET and only consider a few functions to interact with the glasses. Note on code design: in a real world application, you would register a handler in a service in .NET - as their "Dependency Injection" is very good. But this code will be sufficient to demonstrate the interface with the glasses. **So let's go!** Well start off again with the last project [.NET MAUI - Handling taps](/books/vuzix/page/net-maui-handling-taps ".NET MAUI - Handling taps") 1. Update the Nuget package, we require at least [VuzixSDK 1.0.1](https://www.nuget.org/packages/VuzixSDK/) 2. Change the event functions in the **MainActivity** to send the events via the **WeakReferenceMessenger** [![image.png](/uploads/images/gallery/2024-10/scaled-1680-/01Ximage.png)](/uploads/images/gallery/2024-10/01Ximage.png) ```java public void OnTap(int tapCount) { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnTap() { tapCount = tapCount }); } private void onDisplayOff() { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnDisplayOff()); } private void onDisplayOn() { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnDisplayOn()); } private void onDisplayTimeout() { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnDisplayTimeout()); } private void OnPowerButtonPress(bool turningOn) { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnPowerButtonPress() { turningOn = turningOn }); } private void OnScrolled(bool isScreenEmpty) { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnScrolled() { isScreenEmpty = isScreenEmpty }); } ``` Your MainActivy.cs will look as follows: ```java using Android.App; using Android.Content.PM; using Android.OS; using Android.Widget; using CommunityToolkit.Mvvm.Messaging; using VuzixSDK.Class; using Com.Vuzix.Ultralite; using Layout = Com.Vuzix.Ultralite.Layout; using TextAlignment = Com.Vuzix.Ultralite.TextAlignment; using VuzixSDK.Enum; using Android.Graphics; using System.Diagnostics.Tracing; using static System.Net.Mime.MediaTypeNames; namespace MauiApp1 { [Activity(Theme = "@style/Maui.SplashTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation | ConfigChanges.UiMode | ConfigChanges.ScreenLayout | ConfigChanges.SmallestScreenSize | ConfigChanges.Density)] public class MainActivity : MauiAppCompatActivity, Com.Vuzix.Ultralite.IEventListener { IUltraliteSDK _sdk; protected override void OnCreate(Bundle savedInstanceState) { base.OnCreate(savedInstanceState); try { WeakReferenceMessenger.Default.Register(this, (sender, e) => { processUltraLiteError(e); }); WeakReferenceMessenger.Default.Register(this, (sender, e) => { processUltraLiteMessage(e.Data); }); WeakReferenceMessenger.Default.Register(this, (sender, e) => { processUltraLiteOperation(e); }); _sdk = Com.Vuzix.Ultralite.IUltraliteSDK.Get(this); _sdk.AddEventListener(this); } catch (System.Exception ex) { showMessage(ex.Message); } } public void OnTap(int tapCount) { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnTap() { tapCount = tapCount }); } private void onDisplayOff() { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnDisplayOff()); } private void onDisplayOn() { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnDisplayOn()); } private void onDisplayTimeout() { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnDisplayTimeout()); } private void OnPowerButtonPress(bool turningOn) { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnPowerButtonPress() { turningOn = turningOn }); } private void OnScrolled(bool isScreenEmpty) { WeakReferenceMessenger.Default.Send(new VuzixSDK.Class.Event.UltraLiteOnScrolled() { isScreenEmpty = isScreenEmpty }); } public void clearScreen() { _sdk.Canvas.RemoveText(_lastTextId); _sdk.Canvas.RemoveAnimation(_lastAnimationId); _sdk.Canvas.RemoveImage(_lastImageId); } public void showMessage(string message) { MainThread.BeginInvokeOnMainThread(() => { var toast = Toast.MakeText(this, message, ToastLength.Short); toast.Show(); }); } protected void processUltraLiteError(UltraLiteError error) { if (_sdk.IsConnected) { if (!_sdk.IsControlledByMe) { _sdk.RequestControl(); } if (_sdk.IsControlledByMe) { string _title = $"[Error]{(error.Source != null ? " " + error.Source : "")}"; string _error = (error.Exception != null ? $"Exception : {error.Exception.Message}" : "Error occured"); _sdk.SendNotification(_title, _error); } } } int _lastTextId = -1; int _lastImageId = -1; int _lastAnimationId = -1; protected void processUltraLiteMessage(String message) { if (_sdk.IsConnected) { if (!_sdk.IsControlledByMe) { _sdk.RequestControl(); } if (_sdk.IsControlledByMe) { _sdk.SetLayout(Layout.Canvas, 0, true); bool _messageSucceeded = false; if (_lastTextId >= 0) { _messageSucceeded = _sdk.Canvas.UpdateText(_lastTextId, message); } else { _lastTextId = _sdk.Canvas.CreateText(message, Anchor.Center); _messageSucceeded = (_lastTextId != -1); } if (!_messageSucceeded) { showMessage("Text failed"); } _sdk.Canvas.Commit(); SystemClock.Sleep(1000); } } } protected void processUltraLiteOperation(UltraLiteOperationRequest Request) { if (_sdk.IsConnected) { if (!_sdk.IsControlledByMe) { _sdk.RequestControl(); } if (_sdk.IsControlledByMe) { _sdk.SetLayout(Layout.Canvas, 0, true); if (Request.Operation == eUltraLiteOperation.ShowImage && Request.ImageBitMap != null) { LVGLImage image = loadLVGLImage(Request.ImageBitMap); bool _imageSucceeded = false; if (_lastImageId >= 0) { _imageSucceeded = _sdk.Canvas.UpdateImage(_lastImageId, image); } else { _lastAnimationId = _sdk.Canvas.CreateImage(image, Anchor.Center); _imageSucceeded = (_lastImageId != -1); } if(!_imageSucceeded) showMessage("Image failed"); _sdk.Canvas.Commit(); } if (Request.Operation == eUltraLiteOperation.ShowAnimation && Request.AnimationBitMap != null) { LVGLImage[] image = loadLVGLImage(Request.AnimationBitMap); int _animationDelay = 500; if(_lastAnimationId >= 0) { _sdk.Canvas.RemoveAnimation(_lastAnimationId); } _lastAnimationId = _sdk.Canvas.CreateAnimation(image, Anchor.Center, _animationDelay); if (_lastAnimationId == -1) { showMessage("Animation failed"); } _sdk.Canvas.Commit(); } } } else { showMessage("SDK is not connected"); } } private static Bitmap loadBitmap(byte[] bitmapbytes) { BitmapFactory.Options options = new BitmapFactory.Options(); // https://proandroiddev.com/image-decoding-bitmaps-android-c039790ee07e options.InSampleSize = 2; //options.InTargetDensity = 640 * 2; //options.InTargetDensity = 480 * 8; //options.InScaled = true; options.InPreferredConfig = Bitmap.Config.Argb8888; /* options.InMutable = true; options.InSampleSize = 8; options.OutWidth = 600; options.OutHeight = 400; options.InScaled = scaled;*/ Bitmap bmp = BitmapFactory.DecodeByteArray(bitmapbytes, 0, bitmapbytes.Length, options); return bmp;// resize(bmp, 640, 480); } private static LVGLImage[] loadLVGLImage(List images) { List _images = new List(); foreach (var image in images) { _images.Add(LVGLImage.FromBitmap(loadBitmap(image), LVGLImage.CfIndexed1Bit)); } return _images.ToArray(); } private static LVGLImage loadLVGLImage(byte[] image) { //ColorObject[] _colors = { LVGLImage.IColorMapper.White, LVGLImage.IColorMapper.Mid }; //LVGLImage _img = new LVGLImage(LVGLImage.CfIndexed1Bit, 480, 640, _colors, image); LVGLImage _img2 = LVGLImage.FromBitmap(loadBitmap(image), LVGLImage.CfIndexed1Bit); return _img2; } } } ``` 3\. Go back to the MAUI section, **Home.razor** and add the following code. The OnInitialized() will be called by the framework when the page is ready. Then, we register a listener to a message of type **UltraLiteOnTap** and write some text in a string to show we received it ```c# string _eventText = ""; protected override void OnInitialized() { WeakReferenceMessenger.Default.Register(this, (sender, e) => { _eventText = $"You have tapped {e.tapCount}."; StateHasChanged(); }); } ``` ```c#

Hello, world!

@_eventText @if (MyMessage != null && MyMessage.Length>0 ) {

You wrote: @MyMessage

} ``` We do the same for all the remaining events: ```c# protected override void OnInitialized() { WeakReferenceMessenger.Default.Register(this, (sender, e) => { _eventText = $"You have tapped {e.tapCount}."; StateHasChanged(); }); WeakReferenceMessenger.Default.Register(this, (sender, e) => { _eventText = $"Display off event."; StateHasChanged(); }); WeakReferenceMessenger.Default.Register(this, (sender, e) => { _eventText = $"Display on event."; StateHasChanged(); }); WeakReferenceMessenger.Default.Register(this, (sender, e) => { _eventText = $"Display timeout event."; StateHasChanged(); }); WeakReferenceMessenger.Default.Register(this, (sender, e) => { _eventText = $"Power button press {(e.turningOn? "ON" : "OFF")}"; StateHasChanged(); }); WeakReferenceMessenger.Default.Register(this, (sender, e) => { _eventText = $"Scrolled {(e.isScreenEmpty?"Empty screen":"Non empty screen")}."; StateHasChanged(); }); } ``` At this point, you should be set to build your GUI as imagined. And display them on the glasses with ease.