Exception thrown: 'System.NotImplementedException' in Plugin.BLE.dll Exception thrown: 'System.NotImplementedException' in Plugin.BLE.dll An exception of type 'System.NotImplementedException' occurred in Plugin.BLE.dll but was not handled in user code

Hello,

There are a few possible reasons why this happens:

1. You're referencing the portable/shared version of Plugin.BLE.
2. The platform-specific implementations (Android, iOS, etc.) are not being loaded properly.
3. .NET MAUI uses updated dependency injection and platform-specific loading mechanisms compared to Xamarin.Forms.

Recommended Solution

For the smoothest migration experience, switch to the official Plugin.BLE NuGet package. The NuGet package handles all platform-specific loading automatically.

<PackageReference Include="Plugin.BLE" Version="3.1.0" />

There is also a beta version:

<PackageReference Include="Plugin.BLE" Version="3.2.0-beta.1" />

Alternative: Using Source Code Directly

If you must use the source code version, follow these updated steps for .NET 9:

1. Project References: Ensure you reference the platform-specific Plugin.BLE projects in your MAUI platform folders (Platforms/Android, Platforms/iOS, etc.).
2. Update Target Frameworks: Your Plugin.BLE projects should target:
   • net9.0-android for Android
   • net9.0-ios for iOS
   • net9.0 for shared code
3. Dependency Injection in MauiProgram.cs:

      public static class MauiProgram
      {
          public static MauiApp CreateMauiApp()
          {
              var builder = MauiApp.CreateBuilder();
              builder
                  .UseMauiApp<App>()
                  .ConfigureFonts(fonts =>
                  {
                      fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
                  });
    
              // Register BLE services
              builder.Services.AddSingleton<Plugin.BLE.Abstractions.Contracts.IBluetoothLE>(
                  sp => Plugin.BLE.CrossBluetoothLE.Current);
    
              return builder.Build();
          }
      }
   

4. Platform-Specific Permissions:
   • Android (Platforms/Android/AndroidManifest.xml):

          <uses-permission android:name="android.permission.BLUETOOTH" />
          <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
          <uses-permission android:name="android.permission.BLUETOOTH_SCAN" />
          <uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
          <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
     

   • iOS (Platforms/iOS/Info.plist):

          <key>NSBluetoothAlwaysUsageDescription</key>
          <string>This app uses Bluetooth to connect to BLE devices.</string>
          <key>NSBluetoothPeripheralUsageDescription</key>
          <string>This app uses Bluetooth to connect to BLE devices.</string>
     

5. Runtime Permissions: For Android 12+ (API 31+), ensure you handle runtime permission requests in your application code.
6. Conditional Compilation: Use conditional compilation to include platform-specific logic where necessary:

      #if ANDROID
        // Android-specific BLE initialization
      #elif IOS
        // iOS-specific BLE initialization
      #endif
   

7. Assembly Loading: Ensure the platform-specific assemblies are included in your build output.

I hope this helps you resolve the issue.

References:

• Plugin.BLE
• dotnet-bluetooth-le