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Problem with platform specific code in .NET MAUI and Jetbrains Rider

i am having the following problem. i try to invoke platform specific code in the .NET MAUI from the microsoft tutorial.
https://learn.microsoft.com/en-us/dotnet/maui/platform-integration/invoke-platform-code
The problem here is that it can be compiled and builded with Visual Studio, but with Rider from Jetbrains it cant be compiled.
i m getting the following error message:
DeviceOrientationService.cs(5, 38): [CS8795] Partial method 'DeviceOrientationService.GetOrientation()' must have an implementation part because it has accessibility modifiers.
Anyone got an idea what i am missing?

So the thing is you need to create an implementation for your abstract method on all platform classes for it to be able to build since you are targeting multiple platforms.
So just like you have an implementation in your Android and iOS platforms you need it on others as well.
There is another way as well which is you can create an abstract method with an implementation that already does something on other platforms so assume this method is only relevant on Android and iOS then you would do something like below in this class:
public partial class DeviceOrientationService
{
#if ANDROID || IOS
public partial DeviceOrientation GetOrientation();
#else
public partial DeviceOrientation GetOrientation()
{
return DeviceOrientation.Undefiend;
}
#endif
}
Also if you don't want to support Tizen, Windows or MacCatalyst you can just remove their references from the csproj file and then you can delete their platform folders and you won't need to do the above-mentioned things at all your app will only expect Android and iOS code for the above project.

Namespace 'Windows' not found in Unity UWP app

I'm trying to set up a basic UWP project in Unity and use parts of the Windows namespace.*
However, no matter which part of the Windows namespace I try to import in my script, I always get
CS0246: The type or namespace name 'Windows' could not be found (are you missing a using directive or an assembly reference?)
Build support both for Windows and UWP is set up in Visual Studio and Unity and Windows 10 SDK (10.0.19041.0) is installed. Any other ideas how to fix this?
Based on https://forum.unity.com/threads/windows-storage-is-missing-when-building-for-uwp-hololens.541415/ I would have assumed that Windows is available in Unity for UWP as they were able to fix it there?
Thanks
*In the long run, I am trying to use 'Windows.Devices.Input.Preview' to access Gaze Input in a project that also uses Vuforia and thus needs to be UWP. Other tips on how to combine Gaze Tracking and Marker recognition in Unity are also welcome.

The Windows namespace in Unity is made for Windows PC build only. It won't work for other systems. On the top of the script try to add a
#if UNITY_STANDALONE_WIN
You should add the whole declaration like
#if UNITY_STANDALONE_WIN || UNITY_EDITOR_WIN
Use SpeechRecognitionEngine class
#endif
If you are building for android or ios you will need also to add:
#if UNITY_ANDROID
Use SpeechRecognizer class
#endif
#if UNITY_IOS
Use SFSpeechRecognizer class
#endif

What is causing the 'WrongThreadException' in Unity 3D?

I want to integrate a C++ project in Unity. Unity provides a mechanism called I2CPP (Intermediate Language To C++) which allows to add C++ code to your unity project. I've created a simple C++ class and header in a "Blank App (Universal Windows C++/CX)" project in Visual Studio.
// header
namespace SomeNamespace {
public ref class MyRuntimeClass sealed
{
public:
// Constructor
MyRuntimeClass();
// Method to check if initialized
bool IsClassInitialized();
private:
bool _isRuntimeInitialized = false;
};
}
and
// implementation
using SomeNamespace;
MyRuntimeClass::MyRuntimeClass()
{
_isRuntimeInitialized = true;
}
bool MyRuntimeClass::IsClassInitialized()
{
return _isRuntimeInitialized;
};
I've made in Unity a simple project and made the necessary changes in the Player settings outlined in the documentation. I also added a cube as a game object and attached to the cube a script which uses my C++ code, i.e.
#if ENABLE_WINMD_SUPPORT
using SomeNamespace;
#endif
public class RuntimeSampleUnity : MonoBehaviour
{
#if ENABLE_WINMD_SUPPORT
private MyRuntimeClass _myRuntimeClass;
#endif
// Default MonoBehaviour method
void Start()
{
#if ENABLE_WINMD_SUPPORT
// New instance of runtime class
_myRuntimeClass = new MyRuntimeClass();
// Check to see if we initialized C++ runtime component
var isInit = _myRuntimeClass.IsClassInitialized();
Debug.LogFormat("MyRuntimeClass: {0}", isInit);
#endif
}
}
In a final step, I've added the winmd file from the C++ project to my assets in Unity. The project builds fine, but when I run the project I get an Platform.WrongThreadException: The application called an interface that was marshalled for a different thread. What is causing this exception (and how do I fix it)?
EDIT: To elaborate a bit why I'm doing what I'm doing: Microsoft provides a project which shows how to integrate OpenCV (C++) to HoloLens-based projects. While it provides a UWP project which mixes OpenCV and C#, it doesn't show how to integrate this particular project into Unity. Somebody actually made this possible via I2CPP. While I ran into issues using his Visual Studio 2017 based project into Visual Studio 2019, I've tried to make a minimal example to understand how it (basically) works.

I think you're misunderstanding the concept of IL2CPP.
IL2CPP (Intermediate Language To C++) is a Unity-developed scripting
backend which you can use as an alternative to Mono when building
projects for various platforms. When building a project using IL2CPP,
Unity converts IL code from scripts and assemblies to C++, before
creating a native binary file (.exe, apk, .xap, for example) for your
chosen platform. Some of the uses for IL2CPP include increasing the
performance, security, and platform compatibility of your Unity
projects.
To use C++ you have to write a Native Plugin.

Xamarin Portable Library PCL Preprocessor Platform

I'm trying to create and use de Portable library for a cross platform Xamarin.Forms. But the preprocessor for the platform doesn't seem set when I break in the code.
#if WINDOWS_PHONE || __ANDROID__
Debug.WriteLine("Passed");
#endif
Using step by step I can see all the code between the preprocessor condition be skipped (tried on Android and Windows Phone). But when I try the same thing in the start project it works.
In Visual Studio the code should be highlighted when active but it's not in the PCL.
The preprocessors defined in the startup project should be shared with the library, no ?

PCL doesn't work this way.
Try this:
using Xamarin.Forms;
...
if(Device.OS == TargetPlatform.Android)
Debug.WriteLine("I'm on Android");
else if(Device.OS == TargetPlatform.iOS)
Debug.WriteLine("This is iOS");
Here (https://docs.xamarin.com/guides/cross-platform/application_fundamentals/building_cross_platform_applications/sharing_code_options/)
you can find the appropriate Xamarin article. What you are trying to do is
Shared Assets approach and not PCL approach.

Unity3D is not loading this .NET library, with no obvious reason why

I'm trying to get a third party SDK working with Unity. Here's a download of the files in said SDK: https://dl.dropboxusercontent.com/u/11217331/VSDK.zip
The "_DotNET.dll" is a .NET wrapper for the unmanaged code in the CPP dll. For some reason, Unity doesn't load the .NET dll whatever I try:
I put both DLLs in the Assets/Plugins folder
I am using Unity Pro 4.5.0f6, on Windows 8.1
The SDK "_DotNET.dll" is x86 .NET 2.0, and seems to be completely compatible with Unity's version of Mono
I tried putting both DLLs in the Program Files/Unity/Editor folder, still doesn't load them
I do not have the source to these DLLs so I can't make any changes to them, but everything points at Unity being weird here
There are no errors in the editor log or anywhere that give me a hint to why Unity just completely ignores these DLLs
If you can get this C# script working in Unity by loading these DLLs, please tell me your secrets:
using UnityEngine;
using System.Collections;
using ViconDataStreamSDK;
public class test : MonoBehaviour {
ViconDataStreamSDK.DotNET.Client e;
void Start () {
bool isConnected = e.IsConnected().Connected;
Debug.Log("Is it connected?: " + isConnected.ToString());
}
void Update () {
}
}

Ok, it seems I can load it by going back one Unity version, to 4.3.4f1. No idea why, culprit must be somewhere in the Unity 4.5 patch notes (http://unity3d.com/unity/whats-new/unity-4.5).

You will probably need to put the source code for the C# plugin into the unity and see what actual errors it gives you.