How to make a call once callback in C++winrt using smart pointers

Question

I have to modify an existing Control using the Loaded event from a static member function that has to:

Not storing the revoker into some class member because the code is inside a static function. Also, I don't want to store it somewhere else globally.
The Loaded callback should only be called once, so it needs to revoke itself.

Currently this is my solution

        auto loadedRevoker = new winrt::Microsoft::UI::Xaml::Controls::CommandBar::Loaded_revoker;
        *loadedRevoker = commandBar.Loaded(winrt::auto_revoke, [loadedRevoker](auto&& self, auto&&) {
            //revoke event
            loadedRevoker->revoke();
            delete loadedRevoker;

            //do something
        });

It works, but I want to change it into using smart pointers and couldn't figure out a correct way.

0___________ · Accepted Answer · 2025-09-20 16:40:25Z

1

As you did not provide MRE (ie something whch I could compile) my answer was not tested:

It works, but I want to change it into using smart pointers and couldn't figure out a correct way.

auto revoker = std::make_shared<winrt::Microsoft::UI::Xaml::Controls::CommandBar::Loaded_revoker>();

*revoker = commandBar.Loaded(
    winrt::auto_revoke,
    [revoker](auto&& /*sender*/, auto&& /*args*/)
    {
        // revoke event once, then let shared_ptr go out of scope
        revoker->revoke();

        // do something
    });

or

auto revoker_up = std::make_unique<winrt::Microsoft::UI::Xaml::Controls::CommandBar::Loaded_revoker>();

*revoker_up = commandBar.Loaded(
    winrt::auto_revoke,
    [rev = revoker_up.get(), keep = std::move(revoker_up)](auto&& /*sender*/, auto&& /*args*/)
    {
        rev->revoke();
        // do something
        // keep is destroyed when handler scope ends
    });

answered Sep 20 at 16:40

0___________

71.6k4 gold badges41 silver badges94 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

sz ppeter Sep 20 at 16:58

I added a noisy class that prints out constructor and destructor calls with a shared_ptr in the capture, and the first method seems to work. Curiously the destructor prints after the callback finishes, not on the line revoke.

Collectives™ on Stack Overflow

How to make a call once callback in C++winrt using smart pointers

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related