Complete Guide: Building a Full-Featured MAUI Chat App with Backend API

This guide provides a step-by-step approach to building a cross-platform chat app using .NET MAUI (for the frontend) and ASP.NET Core Web API (for the backend). We'll implement all the requested features, including messaging, group chats, voice/video calls, security, and AI integrations.

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1. Architecture Overview

Frontend:

• .NET MAUI (Mobile & Desktop: Android, iOS, Windows, macOS)

• XAML for UI

• MVVM Pattern (CommunityToolkit.MVVM)

• SignalR for real-time messaging

Backend:

• ASP.NET Core Web API

• SignalR for real-time communication

• Entity Framework Core (SQL Server/PostgreSQL)

• Authentication: JWT + Identity

• File Storage: Azure Blob Storage / AWS S3

• AI Services: Azure Cognitive Services / OpenAI API

Additional Services:

• WebRTC (for voice/video calls)

• Twilio (optional for SMS/2FA)

• Firebase Cloud Messaging (FCM) / Apple Push Notification Service (APNS) for notifications

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2. Step-by-Step Implementation

Step 1: Set Up the Backend API

A. Create ASP.NET Core Web API

bash

dotnet new webapi -n ChatApp.Api
cd ChatApp.Api

B. Install Required Packages

bash

dotnet add package Microsoft.AspNetCore.SignalR
dotnet add package Microsoft.EntityFrameworkCore.SqlServer
dotnet add package Microsoft.AspNetCore.Identity.EntityFrameworkCore
dotnet add package Microsoft.AspNetCore.Authentication.JwtBearer
dotnet add package Azure.Storage.Blobs  # For file uploads

C. Configure SignalR for Real-Time Chat

1. Add SignalR Service (Program.cs):

   csharp

   builder.Services.AddSignalR();

2. Create a ChatHub:

   csharp

   public class ChatHub : Hub
   {
       public async Task SendMessage(string user, string message) =>
           await Clients.All.SendAsync("ReceiveMessage", user, message);
   }

3. Map SignalR Hub:

   csharp

   app.MapHub<ChatHub>("/chatHub");

D. Implement JWT Authentication

1. Configure JWT in Program.cs:

   csharp

   builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
       .AddJwtBearer(options => {
           options.TokenValidationParameters = new TokenValidationParameters {
               ValidateIssuer = true,
               ValidateAudience = true,
               ValidateLifetime = true,
               ValidIssuer = builder.Configuration["Jwt:Issuer"],
               ValidAudience = builder.Configuration["Jwt:Audience"],
               IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(builder.Configuration["Jwt:Key"]))
           };
       });

2. Generate JWT Token:

   csharp

   var token = new JwtSecurityToken(
       issuer: _config["Jwt:Issuer"],
       audience: _config["Jwt:Audience"],
       claims: claims,
       expires: DateTime.Now.AddMinutes(30),
       signingCredentials: credentials
   );
   return new JwtSecurityTokenHandler().WriteToken(token);

E. Database Setup (EF Core)

1. Define AppDbContext:

   csharp

   public class AppDbContext : IdentityDbContext<AppUser> {
       public DbSet<Message> Messages { get; set; }
       public DbSet<Group> Groups { get; set; }
   }

2. Run Migrations:

   bash

   dotnet ef migrations add InitialCreate
   dotnet ef database update

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Step 2: Build the MAUI Frontend

A. Create a MAUI Project

bash

dotnet new maui -n ChatApp.Mobile

B. Install Required Packages

bash

dotnet add package Microsoft.AspNetCore.SignalR.Client
dotnet add package CommunityToolkit.Mvvm
dotnet add package Refit (for API calls)
dotnet add package Plugin.Firebase (for push notifications)

C. Implement SignalR Client

csharp

private HubConnection _hubConnection;

_hubConnection = new HubConnectionBuilder()
    .WithUrl("https://yourapi.com/chatHub")
    .Build();

await _hubConnection.StartAsync();
_hubConnection.On<string, string>("ReceiveMessage", (user, message) => {
    // Update UI
});

D. Key UI Components

1. Chat Page (XAML):

   xml

   <CollectionView ItemsSource="{Binding Messages}">
       <DataTemplate>
           <Frame>
               <Label Text="{Binding Text}" />
           </Frame>
       </DataTemplate>
   </CollectionView>
   <Entry Text="{Binding MessageText}" />
   <Button Command="{Binding SendMessageCommand}" Text="Send" />

2. MVVM ViewModel:

   csharp

   [ObservableProperty]
   private ObservableCollection<Message> _messages;
   
   [RelayCommand]
   private async Task SendMessage() {
       await _hubConnection.SendAsync("SendMessage", Username, MessageText);
   }

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Step 3: Implement Key Features

1. Multimedia Sharing (Images, Videos, Docs)

• Backend API:

  csharp

  [HttpPost("upload")]
  public async Task<IActionResult> UploadFile(IFormFile file) {
      var blobClient = _blobContainer.GetBlobClient(file.FileName);
      await blobClient.UploadAsync(file.OpenReadStream());
      return Ok(blobClient.Uri.ToString());
  }

• MAUI File Picker:

  csharp

  var file = await FilePicker.Default.PickAsync();
  if (file != null) {
      await _apiService.UploadFile(file);
  }

2. Voice Messages

• Use MediaElement in MAUI to record & play audio:

  csharp

  var audioOptions = new AudioOptions { Format = AudioFormat.Default };
  var audioFile = await MediaPicker.Default.CaptureAudioAsync(audioOptions);

3. End-to-End Encryption (E2EE)

• Use libsodium-net:

  csharp

  var keyPair = Sodium.PublicKeyBox.GenerateKeyPair();
  var encrypted = Sodium.SecretBox.Create(message, nonce, keyPair.PrivateKey);

4. Video Calls (WebRTC)

• Use Xamarin.WebRTC or a custom WebRTC implementation:

  csharp

  var peerConnection = new RTCPeerConnection();
  peerConnection.OnIceCandidate += (candidate) => {
      _hubConnection.SendAsync("SendIceCandidate", candidate);
  };

5. AI Features (Smart Replies, Translation)

• Azure Cognitive Services:

  csharp

  var translator = new TextTranslationClient(apiKey);
  var translated = await translator.TranslateAsync(text, "en");

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Step 4: Testing & Deployment

1. Test on Emulators & Real Devices

2. Deploy Backend to Azure/AWS

3. Publish MAUI App to Stores (Google Play, App Store)