If you want to be notified when some dependency property of a control changes, for example, UIElement::Visibility, you can do the following trick. First declare you own dependency property of the same type in some class:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | public ref class MyListener{public: static property Windows::UI::Xaml::DependencyProperty ^ BoundVisibilityProperty { Windows::UI::Xaml::DependencyProperty ^ get() { return boundVisibilityProperty; } } property Windows::UI::Xaml::Visibility BoundVisibility { Windows::UI::Xaml::Visibility get() { return safe_cast<Windows::UI::Xaml::Visibility>(GetValue(boundVisibilityProperty)); } void set(Windows::UI::Xaml::Visibility value) { SetValue(boundVisibilityProperty, value); } } static Windows::UI::Xaml::DependencyProperty ^ boundVisibilityProperty; static void OnBoundVisibilityChanged(DependencyObject^ d, Windows::UI::Xaml::DependencyPropertyChangedEventArgs^ e);}; |
than add the property change callback:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | Windows::UI::Xaml::DependencyProperty^ MyListener::boundVisibilityProperty = Windows::UI::Xaml::DependencyProperty::Register("BoundVisibility", Windows::UI::Xaml::Visibility::typeid, MyListener::typeid, ref new Windows::UI::Xaml::PropertyMetadata(Windows::UI::Xaml::Visibility::Collapsed, ref new Windows::UI::Xaml::PropertyChangedCallback(&MyListener::OnBoundVisibilityChanged)));void MyListener::OnBoundVisibilityChanged(DependencyObject^ d, Windows::UI::Xaml::DependencyPropertyChangedEventArgs^ e){ Windows::UI::Xaml::Visibility new_val = safe_cast<Windows::UI::Xaml::Visibility>(e->NewValue); if (new_val == Windows::UI::Xaml::Visibility::Collapsed) { MyListener ^ page = safe_cast<MyListener ^>(d); //do something if the control is hidden }} |
now the only thing that you need is to bind your property to the control’s Visibility with the following code:
1 2 3 4 5 6 7 | Windows::UI::Xaml::Data::Binding ^ binding = ref new Windows::UI::Xaml::Data::Binding();binding->Source = control;binding->Path = ref new Windows::UI::Xaml::PropertyPath("Visibility");binding->Mode = Windows::UI::Xaml::Data::BindingMode::OneWay;Windows::UI::Xaml::Data::BindingOperations::SetBinding(this, CurrentDialogVisibilityProperty, binding); |
in C# it looks a bit easier, because in C# you do not need to use long namespaces like Windows::UI::Xaml all the time, but if we add using namespace directive in C++:
1 | using namespace Windows::UI::Xaml; |
C++ will not understand the difference between this->Visibility and Windows::UI::Xaml::Visibility.
