How to properly create a property to store any amount of values? - visual-c++

Question

Making the shift from C++ to C++/CX I stumbled upon that ref classes can't have native members in they're public or protected members, due to possible errors with java and stuff. Instead we now have to use properties, which I can make but only to hold 1 value...
The idea was to make a property that would store 4 floats in an array or vector and later pass the values to a XMVECTOR. The relevant code I have in the class header file until now is:
public:
property std::vector<float> num{
void set(std::vector<float> e){
NUM = e;
};
std::vector<float> get(){
return NUM;
};
};
private:
std::vector<float> NUM;
Later in the .cpp file I do:
std::vector<float> g;
g.pushback(3);
num = g;
I also make it a string to pass to a TextBox(but that's not important). In the end I just get many similar errors... The 2 errors are:
error C3986: 'set': signature of public member contains native type 'std::vector<_Ty>'
error C3986: 'set': signature of public member contains native type 'std::allocator<_Ty>'
The only thing I imagine is that I can't use strings or vectors. I know Platform::Strings exist but what about vectors??

Answer 1

Standard C++ types cannot be projected across the WinRT ABI, which is the communication layer shared by all WinRT language projections (C#/VB/JS). As Jagannath mentions, there is a collection interface (Windows::Foundation::Collections::IVector<T>). There is also a dictionary type (IMap<K,V>) and various iterators and support types. These are understood by all languages, but are just interfaces. Each language projection is responsible for authoring runtime classes that implement these interfaces. For C++/Cx, these ref classes are found in the header <collection.h> and are in the namespace Platform::Collections. Platform::Collections::Vector<T> and Platform::Collections::Map<K,V> are the basic types you can use as backing stores. Additionally, Vector<T> can be move-constructed from std::vector<T>.
However, you can't make a public property of type Platform::Collections::Vector<T> either, as this is still a C++ type. What you do instead is create a public property of type Windows::Foundation::Collection::IVector<T> which is backed by a private member variable of type Platform::Collections::Vector<T>.
Essentially:
public:
property Windows::Foundation::Collections::IVector<float>^ num{
Windows::Foundation::Collections::IVector<float>^ get(){
return NUM;
}
}
private:
Platform::Collections::Vector<float>^ NUM;
I have avoided mentioning the property setter, because that gets tricky (your private type would need to also be an IVector and it will only be a Platform::Collections::Vector if it came from C++).

Answer 2

You could use Windows::Foundation::Collections::IVector<float>^ for the signatures. I could not test this as I don't have the compiler at hand.

Answer 3

Hey guys I managed to get this working so I thought I'll post the code. The header file goes like this:
public:
property Windows::Foundation::Collections::IVector<int>^ num{
void set(Windows::Foundation::Collections::IVector<int>^ e){
NUM = safe_cast<Platform::Collections::Vector<int>^>(e);
};
Windows::Foundation::Collections::IVector<int>^ get(){
return NUM;
};
};
private:
Platform::Collections::Vector<int>^ NUM;
And in the .cpp file the code is:
num = ref new Vector<int>;
num->Append(5);
num->Append(54);
TextBox1->Text = num->GetAt(0).ToString() + "\n" + num->GetAt(1).ToString();
The result will have written the values 5 and 54 to a TextBox.