What does the IntelliSense error "public data members are not allowed in non-value types" mean?

Question

I'm taking over a C++ CLI project and one of the files, StartScreen.xaml.h, is throwing an IntelliSense error in Visual Studio 2013. Here's a fragment of the code:

public ref class StartScreen sealed
{
public:
    StartScreen();

    void SetApp(App^ app);

    void ShowProgressRing();
    void HideProgressRing();

internal:
    static float imagePercentage;
    ....

It's that last line that's causing the problem. imagePercentage throws the error

108 IntelliSense: public data members are not allowed in non-value types

What does this mean and how (if at all - it compiles without compiler errors) should I fix it?

Answer 1

I would guess it is just a bug in IntelliSense. C++/CLI and C++/CX share a syntax, but it seems that there are some rules that are different. In this case, C++/CX doesn't allow public/internal fields:

• http://social.msdn.microsoft.com/Forums/windowsapps/en-US/20db7069-3e49-4772-8b9a-0c80490e0dea/error-c3984-a-nonvalue-type-cannot-have-any-public-data-members?forum=winappswithnativecode
• http://msdn.microsoft.com/en-us/library/windows/apps/hh699870

C++/CLI has no such restriction (that's why it compiles for you). The Intellisense is probably just (incorrectly) sharing this rule between both C++/CLI and C++/CX.

If you really do want an internally visible field, I would just ignore the Intellisense. If it bothers you, and you can change it to a property, then that's your workaround.