error related to winrt::impl::com_ref<winrt::hstring> when converting from c++/cx to c++/winrt

Question

In cppcx, I used to have this:

auto button = safe_cast<ContentControl ^>(obj);
if (auto text = dynamic_cast<Platform::String^>(button->Content)) {
    return text->Data();
}

When I try to do this to convert this code to cppwinrt:

auto button = obj.as<winrt::ContentControl>();
if (auto text = button.Content().try_as<winrt::hstring>()) {
    return text.c_str();
}

I get the following error:

Error (active) E0312 no suitable user-defined conversion from "winrt::impl::com_refwinrt::hstring" to "wchar_t*" exists

I was hoping I would get a winrt::hstring as a result of the try_as and I can get the .c_str() from it, but I am getting a winrt::impl::com_refwinrt::hstring instead. What am I missing?

Answer 1

It looks like you want to unbox a scalar value behind an IInspectable interface (see Boxing and unboxing scalar values to IInspectable with C++/WinRT). For unboxing you'll want to use the unbox_value function template:

auto button = obj.as<winrt::ContentControl>();
if (auto text = unbox_value<winrt::hstring>(button.Content())) {
    return text.c_str();
}

Although it's questionable, whether you really want to return a pointer that points into the middle of some data owned elsewhere. It's probably best to just return an hstring by value. String handling in C++/WinRT has more information on the topic.