how to use own GUI / windows instead VSTI GUI?

Developer VST 3 SDK
5

From quick look,

  1. I am not expert, but I think you should use AssemblyResolver instead load assembly directly.
System::Reflection::Assembly ^ WPF::WApp::MyResolveEventHandler(System::Object ^ sender, System::ResolveEventArgs ^ args)
{
                        bool ok = false;
                        try {
				result = Assembly::LoadFrom(assemblyPath);
				ok = true;
			}
			catch (Exception ^e)
			{
				LoggerCPPInt::mf_writeLog("C++/CLI", "MyResolveEventHandler()", "LOAD FAILED", msc::convert_to_string(e->ToString()));
			}
	if (ok == true)
	{
		return result;
	}
	else
	{
		return args->RequestingAssembly;
	}
}

// ==========================================================
// Somewhere where you initialize WPF
AppDomain ^cd = AppDomain::CurrentDomain;
cd->AssemblyResolve += gcnew ResolveEventHandler(WPF::WApp::MyResolveEventHandler);

This is worked for me if I used UserControl only.

  1. your function for get HWND need to be corrected to this
MeterWpfWrapper::MeterWpfWrapper(void ** hWnd) { .. }
// then call
m_UI = std::make_shared<MeterWpfWrapper>(&m_parentWindow);

I don’t know how you then attach the HWND in to HostWindow but this is how I did it

	if (h == nullptr)
	{
		wpfi->mf_Window_GetPointer(&h);
		SetParent((HWND)h, (HWND)systemWindow);
	}