它似乎与继承有关：

It seems to have something to do with the inheriance:

部分ref类MainPage：public Windows :: UI :: Xaml :: Controls :: UserControl ，...

partial ref class MainPage: public Windows::UI::Xaml::Controls::UserControl, ...

但问题仍然是：为什么 是否未调用destuctor？

but still the question: why is the destuctor not called?