get_factory_from.cpp

#include <Windows.h>
#include "winrt/Windows.Globalization.h"

template <typename Class, typename Interface = winrt::Windows::Foundation::IActivationFactory>
Interface get_factory_from(winrt::param::hstring const& library_name)
{
    winrt::impl::library_handle library(winrt::impl::load_library(static_cast<winrt::hstring const&>(library_name).c_str()));

    if (!library)
    {
        return nullptr;
    }

    winrt::param::hstring class_name = winrt::name_of<Class>();

    auto library_call = reinterpret_cast<int32_t(__stdcall*)(void* classId, void** factory)>(WINRT_IMPL_GetProcAddress(library.get(), "DllGetActivationFactory"));

    if (!library_call)
    {
        return nullptr;
    }

    winrt::Windows::Foundation::IActivationFactory library_factory;

    if (0 != library_call(*(void**)(&class_name), winrt::put_abi(library_factory)))
    {
        return nullptr;
    }

    Interface result;

    if constexpr (std::is_same_v<Interface, winrt::Windows::Foundation::IActivationFactory>)
    {
        result = library_factory;
    }
    else
    {
        result = library_factory.try_as<Interface>();
    }

    if (result)
    {
        library.detach();
    }

    return result;
}

template <typename Class>
Class activate_from(winrt::param::hstring const& library_name)
{
    auto factory = get_factory_from<Class, winrt::Windows::Foundation::IActivationFactory>(library_name);

    if (!factory)
    {
        return nullptr;
    }

    return factory.ActivateInstance<Class>();
}

int main()
{
    CO_MTA_USAGE_COOKIE cookie{};
    CoIncrementMTAUsage(&cookie);

    using namespace winrt::Windows::Globalization;

    auto factory = get_factory_from<Calendar>(L"Windows.Globalization.dll");

    if (factory)
    {
        auto calendar = factory.ActivateInstance<Calendar>();
        assert(calendar.Year() == 2025);
    }

    auto calendar = activate_from<Calendar>(L"Windows.Globalization.dll");

    if (calendar)
    {
        assert(calendar.Year() == 2025);
    }
}