Service cleanup (#282)

Encapsulate the WebAssembly specific bits into a service abstraction,
that allows the MAUI bits to be independently implemented/ignored
without throwing exception, or handling try/catch.

Author: IEvangelist

app/SharedWebComponents/Components/VoiceDialog.razor.cs

@@ -12,6 +12,8 @@ public sealed partial class VoiceDialog : IDisposable
 
     [Inject] public required ISpeechSynthesisService SpeechSynthesis { get; set; }
 
+    [Inject] public required ITextToSpeechPreferencesListener VoiceChangesListener { get; set; }
+
     [Inject] public required ILocalStorageService LocalStorage { get; set; }
 
     [CascadingParameter] public required MudDialogInstance Dialog { get; set; }
@@ -22,19 +24,7 @@ protected override async Task OnInitializedAsync()
 
         await GetVoicesAsync();
 
-        try
-        {
-            SpeechSynthesis.OnVoicesChanged(() => GetVoicesAsync(true));
-        }
-        catch
-        {
-            // TODO: Find a better way to do this
-            // The Blazor.SpeechSynthesis.WebAssembly API supports listening to changes,
-            // however the underlying code does not do this using a DI-friendly way.
-            // The code assumes the concrete implementation for the ISpeechSynthesisService
-            // service is the concrete Web Assembly type which is not valid.
-            // There is no alternative API that MAUI apps can use.
-        }
+        VoiceChangesListener.OnAvailableVoicesChanged(() => GetVoicesAsync(true));
 
         _voicePreferences = new VoicePreferences(LocalStorage);
 
@@ -70,19 +60,7 @@ private void OnValueChanged(string selectedVoice) => _voicePreferences = _voiceP
 
     public void Dispose()
     {
-        try
-        {
-            SpeechSynthesis.UnsubscribeFromVoicesChanged();
-        }
-        catch
-        {
-            // TODO: Find a better way to do this
-            // The Blazor.SpeechSynthesis.WebAssembly API supports listening to changes,
-            // however the underlying code does not do this using a DI-friendly way.
-            // The code assumes the concrete implementation for the ISpeechSynthesisService
-            // service is the concrete Web Assembly type which is not valid.
-            // There is no alternative API that MAUI apps can use.
-        }
+        VoiceChangesListener.UnsubscribeFromAvailableVoicesChanged();
     }
 }
 

app/SharedWebComponents/Pages/VoiceChat.razor.cs

@@ -79,6 +79,7 @@ private void OnSendPrompt()
                                 Name = voice
                             };
                         }
+
                         try
                         {
                             SpeechSynthesis.Speak(utterance, duration =>
@@ -95,9 +96,7 @@ private void OnSendPrompt()
                             // The code assumes the concrete implementation for the ISpeechSynthesisService
                             // service is the concrete Web Assembly type which is not valid. However, the
                             // alternate API is something MAUI can implement.
-
                             SpeechSynthesis.Speak(utterance);
-
                             _isReadingResponse = false;
                             StateHasChanged();
                         }

app/SharedWebComponents/Services/ITextToSpeechPreferencesListener.cs

@@ -0,0 +1,10 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+namespace SharedWebComponents.Services;
+
+public interface ITextToSpeechPreferencesListener
+{
+    void OnAvailableVoicesChanged(Func<Task> onVoicesChanged);
+
+    void UnsubscribeFromAvailableVoicesChanged();
+}

app/frontend/Program.cs

@@ -18,6 +18,7 @@
 builder.Services.AddSessionStorageServices();
 builder.Services.AddSpeechSynthesisServices();
 builder.Services.AddSpeechRecognitionServices();
+builder.Services.AddSingleton<ITextToSpeechPreferencesListener, TextToSpeechPreferencesListenerService>();
 builder.Services.AddMudServices();
 builder.Services.AddTransient<IPdfViewer, WebPdfViewer>();
 

app/frontend/Services/TextToSpeechPreferencesListenerService.cs

@@ -0,0 +1,15 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using Microsoft.JSInterop;
+
+namespace ClientApp.Services;
+
+public sealed class TextToSpeechPreferencesListenerService(
+    ISpeechSynthesisService speechSynthesisService) : ITextToSpeechPreferencesListener
+{
+    public void OnAvailableVoicesChanged(Func<Task> onVoicesChanged) =>
+        speechSynthesisService.OnVoicesChanged(onVoicesChanged);
+
+    public void UnsubscribeFromAvailableVoicesChanged() =>
+        speechSynthesisService.UnsubscribeFromVoicesChanged();
+}

app/maui-blazor/MauiProgram.cs

@@ -33,6 +33,7 @@ public static MauiApp CreateMauiApp()
 		builder.Services.AddSingleton<ISessionStorageService, MauiSessionStorageService>();
 		builder.Services.AddSingleton<ISpeechRecognitionService, MauiSpeechRecognitionService>();
 		builder.Services.AddSingleton<ISpeechSynthesisService, MauiSpeechSynthesisService>();
+        builder.Services.AddSingleton<ITextToSpeechPreferencesListener, MauiSpeechSynthesisService>();
 		builder.Services.AddTransient<IPdfViewer, MauiPdfViewer>();
 
 		builder.Services.AddMudServices();

app/maui-blazor/Services/MauiSpeechRecognitionService.cs

@@ -2,12 +2,13 @@
 
 namespace MauiBlazor.Services;
 
-public class MauiSpeechRecognitionService(ISpeechToText speechToText) : ISpeechRecognitionService
+public sealed class MauiSpeechRecognitionService(ISpeechToText speechToText) : ISpeechRecognitionService
 {
     private SpeechRecognitionOperation? _current;
 
     public void CancelSpeechRecognition(bool isAborted)
     {
+        _ = isAborted;
         _current?.Dispose();
     }
 
@@ -19,6 +20,7 @@ public ValueTask DisposeAsync()
 
     public Task InitializeModuleAsync(bool logModuleDetails = true)
     {
+        _ = logModuleDetails;
         return Task.CompletedTask;
     }
 

app/maui-blazor/Services/MauiSpeechSynthesisService.cs

@@ -2,9 +2,11 @@
 
 namespace MauiBlazor.Services;
 
-public class MauiSpeechSynthesisService : ISpeechSynthesisService
+public class MauiSpeechSynthesisService(ITextToSpeech textToSpeech)
+    : ISpeechSynthesisService, ITextToSpeechPreferencesListener
 {
     private CancellationTokenSource? _cts;
+    private Task? _speakTask;
 
     public bool Paused => throw new NotImplementedException();
 
@@ -28,6 +30,11 @@ public ValueTask<SpeechSynthesisVoice[]> GetVoicesAsync()
         return ValueTask.FromResult<SpeechSynthesisVoice[]>([voice]);
     }
 
+    public void OnAvailableVoicesChanged(Func<Task> onVoicesChanged)
+    {
+        _ = onVoicesChanged;
+    }
+
     public void Pause()
     {
         Cancel();
@@ -40,35 +47,44 @@ public void Resume()
         // TODO: support pause & resume
     }
 
-    public async void Speak(SpeechSynthesisUtterance utterance)
+    public void Speak(SpeechSynthesisUtterance utterance)
     {
+        _cts?.Cancel();
         _cts = new();
 
-        var current = CultureInfo.CurrentUICulture.Name;
-
-        var locales = await TextToSpeech.Default.GetLocalesAsync();
-        var localeArray = locales.ToArray();
-        var locale = localeArray.FirstOrDefault(l => current == $"{l.Language}-{l.Country}");
-        if (locale is null)
+        _speakTask = Task.Run(async () =>
         {
-            // an exact match was not found, try just the lang
-            var split = current.Split('-');
-            if (split.Length == 1 || split.Length == 2)
+            var current = CultureInfo.CurrentUICulture.Name;
+
+            var locales = await textToSpeech.GetLocalesAsync();
+            var localeArray = locales.ToArray();
+            var locale = localeArray.FirstOrDefault(l => current == $"{l.Language}-{l.Country}");
+            if (locale is null)
             {
-                // try the first part (or the whole thing if it is just lang)
-                locale = localeArray.FirstOrDefault(l => split[0] == $"{l.Language}");
+                // an exact match was not found, try just the lang
+                var split = current.Split('-');
+                if (split.Length is 1 or 2)
+                {
+                    // try the first part (or the whole thing if it is just lang)
+                    locale = localeArray.FirstOrDefault(l => split[0] == $"{l.Language}");
+                }
+                else
+                {
+                    // just go with the first one
+                    locale = localeArray.FirstOrDefault();
+                }
             }
-            else
+
+            var options = new SpeechOptions
             {
-                // just go with the first one
-                locale = localeArray.FirstOrDefault();
-            }
-        }
+                Locale = locale
+            };
 
-        var options = new SpeechOptions
-        {
-            Locale = locale
-        };
-        await TextToSpeech.Default.SpeakAsync(utterance.Text, options, _cts.Token);
+            await textToSpeech.SpeakAsync(utterance.Text, options, _cts.Token);
+        }, _cts.Token);
+    }
+
+    public void UnsubscribeFromAvailableVoicesChanged()
+    {
     }
 }