Can't use IVector<T> in my value struct?

Question

I would like to have a vector of value structs in another value struct:

public value struct HttpHeader
{
   Platform::String^ mName;
   Platform::String^ mValue;

};

typedef Windows::Foundation::Collections::IVector<HttpHeader> IHttpHeaders;

public value struct HttpRequestEvent
{
   uint32 mHandle;
   IHttpHeaders^ mHeaders;

};

However I get this error on compilation:

error C3992: 'mHeaders': signature of public member contains invalid type 'myNamespace::IHttpHeaders ^' 

If this isn't possible, can someone recommend another way of implementing this?

Answer 1

Hello,

Value structs can only have public fields, only allow fundamental types and Strings as members. Parameters of type value struct can only be passed by value.

Runtime classes/structs on the other hand have an internal ref-count, allow public/private/internal methods, properties & events as well as private/internal fields. Parameter of type runtime class get passed by reference.

To understand more about runtime classes, start by reading this MSDN topic: http://msdn.microsoft.com/en-us/library/windows/apps/hh699870(v=vs.110).aspx

Hope this helps,
Marian Luparu
Visual C++

Answer 2

I would like to have a vector of value structs in another value struct:

public value struct HttpHeader
{
   Platform::String^ mName;
   Platform::String^ mValue;

};

typedef Windows::Foundation::Collections::IVector<HttpHeader> IHttpHeaders;

public value struct HttpRequestEvent
{
   uint32 mHandle;
   IHttpHeaders^ mHeaders;

};

However I get this error on compilation:

error C3992: 'mHeaders': signature of public member contains invalid type 'myNamespace::IHttpHeaders ^' 

If this isn't possible, can someone recommend another way of implementing this?

请问这个问题有具体的代码可以参考下吗？

Answer 3

A value struct can only have other value structs or intrinsic types as members. mHeaders in your example is not - it's a reference type. That's why you're getting the compile-time error.

If you need to store a vector of interfaces, the underlying class should either be a standard C++ class or a ref class. It really depends on what you're planning to use this type for. If it's only for use internally in your code, make it a standard C++ class:

struct HttpRequestEvent {  
    uint32 mHandle;  
    IHttpHeaders^ mHeaders;
};

If this needs to go over an WinRT boundary, make it a ref-class: 

ref struct HttpRequestEvent {
    property uint32 Handle;
    property IHttpHeaders^ Headers;
}; 

 

Hope this helps,
Marian Luparu
Visual C++