Is it possible to add a static event to an attached property and lazy-initialize it?

[sxlllslgh]

I'd like to instantly change the language for an unpackaged application. As I known that the PrimaryLanguageOverride was not able for unpackaged applications, I thought it might be possible utilizing attached properties and events inspired by WinUI3Localizer. But it was written by C#, and I was developing with C++/WinRT, so there were a lot problems I need to resolve.

Follow the UWP guide I wrote a customed attached property to implement a custom Uid, the header of which is like:

struct UidTrans : UidTransT<UidTrans>, winrt::Microsoft::UI::Xaml::DependencyObject {
private:
    static winrt::Microsoft::UI::Xaml::DependencyProperty uidProperty;
    static winrt::event<winrt::Windows::Foundation::EventHandler<winrt::Microsoft::UI::Xaml::DependencyObject>> uidTransSetEvent;

public:
    static void Initialize();
    static winrt::Microsoft::UI::Xaml::DependencyProperty UidProperty() { return uidProperty; }
    static winrt::hstring GetUid(const winrt::Microsoft::UI::Xaml::DependencyObject& target);
    static void SetUid(const winrt::Microsoft::UI::Xaml::DependencyObject& target, const winrt::hstring& uid);
    static winrt::event_token UidTransSet(winrt::Windows::Foundation::EventHandler<winrt::Microsoft::UI::Xaml::DependencyObject> const& handler);
    static void UidTransSet(winrt::event_token const& token) noexcept;
};

In the cpp file, the static member properties need to be assgined with null, so that the lazy initialization could be implemented to avoid link error:

// Assign static member properties to null to avoid static initialization order fiasco.
winrt::Microsoft::UI::Xaml::DependencyProperty UidTrans::uidProperty = nullptr;
// ERROR: winrt::event cannot be assigned with nullptr
winrt::event<winrt::Windows::Foundation::EventHandler<winrt::Microsoft::UI::Xaml::DependencyObject>> uidTransSetEvent = nullptr;

// Static initialization function.
void UidTrans::Initialize() {
    uidProperty = winrt::Microsoft::UI::Xaml::DependencyProperty::RegisterAttached(L"Uid", winrt::xaml_typename<winrt::hstring>(), winrt::xaml_typename<DynamicScanDiagnosis::UidTrans>(), winrt::Microsoft::UI::Xaml::PropertyMetadata{ winrt::box_value(L"") });
    // ERROR: The operator "=" of winrt::event has been deleted.
    uidTransSetEvent = winrt::event<winrt::Windows::Foundation::EventHandler<winrt::Microsoft::UI::Xaml::DependencyObject>>();
}

winrt::hstring UidTrans::GetUid(const winrt::Microsoft::UI::Xaml::DependencyObject& target) {
    return winrt::unbox_value<winrt::hstring>(target.GetValue(uidProperty));
}

void UidTrans::SetUid(const winrt::Microsoft::UI::Xaml::DependencyObject& target, const winrt::hstring& uid) {
    target.SetValue(uidProperty, winrt::box_value(uid));
    uidTransSetEvent.add(target);
}

winrt::event_token UidTrans::UidTransSet(winrt::Windows::Foundation::EventHandler<winrt::Microsoft::UI::Xaml::DependencyObject> const& handler) {
    return uidTransSetEvent.add(handler);
}

void UidTrans::UidTransSet(winrt::event_token const& token) noexcept {
    uidTransSetEvent.remove(token);
}

To make the static properties lazy-initialized, the initialized function is called in App.xaml.cpp:

App::App() {
    UidTrans::Initialize();
    InitializeComponent();
}

So the problem seems that how to lazy-initialize the winrt::event? Or is it possible?
Thank you.

[DarranRowe]

Event is a structure, but it isn't a smart pointer class like winrt::Microsoft::UI::Xaml::DependencyProperty or winrt::Microsoft::UI::Xaml::DependencyObject. So the only way to have lazy initialisation on event is to use std::optional or a pointer (std::unique_pointer would be preferred for lifetime reasons.)
It isn't, however, much of a problem to just initialise it as is, since it doesn't contain anything too big on construction.

[sxlllslgh]

It works, thank you very much! Finally I used a smart pointer to resovle it.