ReactiveUI.WinUI not found.

[Haale]

I don't use that ReactiveUI.WinUI dll, but it outputs a warning when runing the code ViewModel = new MainViewModel(); which lies in my constructor of main Form. My environment:.
NET Framwork 4.8 + WinForm+Vs2017 +C# + ReactiveUI v20.1.0.0+ ReactiveUI.Winform v20.1.0.0.
Following is my code:

(1)model:

public class User
 {
     public string Name { get; set; }
     public int ID { get; set; }
 }

(2)viewmodel:

public class MainViewModel:ReactiveObject
    {
        private User _user;

        //public MainViewModel(User u)
        //{
        //    _user = u;
        //    SaveCommand = ReactiveCommand.Create(Save);
        //}
        public MainViewModel()
        {
            _user = new User();
            SaveCommand = ReactiveCommand.Create(Save);
        }
        public User User
        {
            get => _user;
            set => this.RaiseAndSetIfChanged(ref _user, value);
        }

        public ReactiveCommand<Unit, Unit> SaveCommand { get; }

        private void Save()
        {
            
            System.Windows.Forms.MessageBox.Show($"User Name: {_user.Name}");
        }
    }

(3)main form view:

public partial class Form1 : Form, IViewFor<MainViewModel>
    {
        public MainViewModel ViewModel { get; set; }

        object IViewFor.ViewModel
        {
            get => ViewModel;
            set => ViewModel = (MainViewModel)value;
        }
        User us = new User() { Name = "hkk", ID = 100 };
        public Form1()
        {
            
            AppDomain.CurrentDomain.FirstChanceException += (sender, eventArgs) =>
            {
                Console.WriteLine(eventArgs.Exception.ToString());
            };
            InitializeComponent();
            
            ViewModel = new MainViewModel();
            this.WhenActivated(disposables =>
            {
           
                this.WhenAnyValue(x => x.ViewModel.User.ID)
                .BindTo(this, x => x.textBox1.Text)
                .DisposeWith(disposables);

          
               this.BindCommand(ViewModel, vm => vm.SaveCommand, v => v.button4)
                    .DisposeWith(disposables);
            });
        }
}

here's the console output when the debugger hit the breakpoint at "ViewModel = new MainViewModel();"line:

“ReativeUITest.exe”(CLR v4.0.30319: ReativeUITest.exe): Loaded "...\ReativeUITest\ReativeUITest\bin\Debug\System.Reactive.dll". Cannot find or open the PDB file.
“ReativeUITest.exe”(CLR v4.0.30319: ReativeUITest.exe): Loaded "C:\Windows\Microsoft.Net\assembly\GAC_MSIL\netstandard\v4.0_2.0.0.0__cc7b13ffcd2ddd51\netstandard.dll". Module was built without symbols.
“ReativeUITest.exe”(CLR v4.0.30319: ReativeUITest.exe): Loaded "...\ReativeUITest\ReativeUITest\bin\Debug\System.ValueTuple.dll". Cannot find or open the PDB file.
Exception thrown: "System.IO.FileNotFoundException" in mscorlib.dll
“ReativeUITest.exe”(CLR v4.0.30319: ReativeUITest.exe): Loaded "C:\Windows\Microsoft.Net\assembly\GAC_MSIL\mscorlib.resources\v4.0_4.0.0.0_zh-Hans_b77a5c561934e089\mscorlib.resources.dll". Module was built without symbols.
System.IO.FileNotFoundException: Could not load file or assembly "ReactiveUI.XamForms, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null" or one of its dependencies. The system cannot find the file specified.
File name: "ReactiveUI.XamForms, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null"
   at System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
   at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)

=== Pre-bind state information ===
LOG: DisplayName = ReactiveUI.XamForms, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null
 (Fully-specified)
LOG: Appbase = file:.../ReativeUITest/ReativeUITest/bin/Debug/
LOG: Initial PrivatePath = NULL
Calling assembly: ReactiveUI, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null.
===
LOG: This bind starts in default load context.
LOG: Using application configuration file: ...\ReativeUITest\ReativeUITest\bin\Debug\ReativeUITest.exe.Config
LOG: Using host configuration file: 
LOG: Using machine configuration file from ...\Framework64\v4.0.30319\config\machine.config.
LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind).
LOG: Attempting download of new URL file:.../ReativeUITest/ReativeUITest/bin/Debug/ReactiveUI.XamForms.DLL.
LOG: Attempting download of new URL file:///.../ReativeUITest/ReativeUITest/bin/Debug/ReactiveUI.XamForms/ReactiveUI.XamForms.DLL.
LOG: Attempting download of new URL file:.../ReativeUITest/ReativeUITest/bin/Debug/ReactiveUI.XamForms.EXE.
LOG: Attempting download of new URL file:.../ReativeUITest/ReativeUITest/bin/Debug/ReactiveUI.XamForms/ReactiveUI.XamForms.EXE.

“ReativeUITest.exe”(CLR v4.0.30319: ReativeUITest.exe): Loaded "...\ReativeUITest\ReativeUITest\bin\Debug\ReactiveUI.Winforms.dll".
Exception thrown: "System.IO.FileNotFoundException" in mscorlib.dll
System.IO.FileNotFoundException: Could not load file or assembly "ReactiveUI.Wpf, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null" or one of its dependencies. The system cannot find the file specified.
File name: "ReactiveUI.Wpf, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null"
   at System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
   at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)

=== Pre-bind state information ===
LOG: DisplayName = ReactiveUI.Wpf, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null
 (Fully-specified)
LOG: Appbase = file.../ReativeUITest/ReativeUITest/bin/Debug/
LOG: Initial PrivatePath = NULL
Calling assembly: ReactiveUI, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null.
===
LOG: This bind starts in default load context.
LOG: Using application configuration file: ...\ReativeUITest\ReativeUITest\bin\Debug\ReativeUITest.exe.Config
LOG: Using host configuration file: 
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework64\v4.0.30319\config\machine.config.
LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind).
LOG: Attempting download of new URL file:.../ReativeUITest/ReativeUITest/bin/Debug/ReactiveUI.Wpf.DLL.
LOG: Attempting download of new URL file:///.../ReativeUITest/ReativeUITest/bin/Debug/ReactiveUI.Wpf/ReactiveUI.Wpf.DLL.
LOG: Attempting download of new URL file:.../ReativeUITest/ReativeUITest/bin/Debug/ReactiveUI.Wpf.EXE.
LOG: Attempting download of new URL file:.../ReativeUITest/ReativeUITest/bin/Debug/ReactiveUI.Wpf/ReactiveUI.Wpf.EXE.

Exception thrown: "System.IO.FileNotFoundException" in mscorlib.dll
System.IO.FileNotFoundException: Could not load file or assembly "ReactiveUI.Uno, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null" or one of its dependencies. The system cannot find the file specified.
File name: "ReactiveUI.Uno, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null"
   at System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
   at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)

=== Pre-bind state information ===
LOG: DisplayName = ReactiveUI.Uno, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null
 (Fully-specified)
LOG: Appbase = file:.../ReativeUITest/ReativeUITest/bin/Debug/
LOG: Initial PrivatePath = NULL
Calling assembly: ReactiveUI, Version=20.1.0.0, Culture=neutral, PublicKeyToken=null.
===
LOG: This bind starts in default load context.
LOG: Using application configuration file: ...\ReativeUITest\ReativeUITest\bin\Debug\ReativeUITest.exe.Config
LOG: Using host configuration file: 
LOG: Using machine configuration file from ...\Microsoft.NET\Framework64\v4.0.30319\config\machine.config.
LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind).
LOG: Attempting download of new URL file:.../ReativeUITest/ReativeUITest/bin/Debug/ReactiveUI.Uno.DLL.
LOG: Attempting download of new URL file:///.../ReativeUITest/ReativeUITest/bin/Debug/ReactiveUI.Uno/ReactiveUI.Uno.DLL.
LOG: Attempting download of new URL file:.../ReativeUITest/Reative

[dpvreony]

take a look at

#3786 (comment)

see if the following workaround prevents the issue. you need one of these in app initialisation before ReactiveUI is called.

if you're not doing any custom Splat DI config.

ReactiveUI.PlatformRegistrationManager.SetRegistrationNamespaces(RegistrationNamespace.WinUI);

if you're doing any custom config to Splat etc. you'll need something along the lines of. (you might want this version anyway so it's clearer when ReactiveUI is being set up)

Locator.CurrentMutable.InitializeSplat();
Locator.CurrentMutable.InitializeReactiveUI(RegistrationNamespace.WinUI); 

If the Assembly scanning is the issue, this should prevent it.

you'll want to use RegistrationNamespace.Winforms

[Haale]

Thank you. I forgot to change the RegistrationNamespace.WinUI to RegistrationNamespace.WinForm for my Winform App. Problem is solved now.

For the people who follow this disccussion or some issue about that, when you add
ReactiveUI.PlatformRegistrationManager.SetRegistrationNamespaces(RegistrationNamespace.WinUI);

or

Locator.CurrentMutable.InitializeSplat();
Locator.CurrentMutable.InitializeReactiveUI(RegistrationNamespace.WinUI); 

don't forgot to adapt the enum config RegistrationNamespace.WinUI to whatever framework (WinUI, WinForm,WPF or others) you use.