How do I import and call linphone_core_get_calls in vb?

Question

The API reference in question is located here.

I need to know how to properly DLLImport and then use this in vb:

const bctbx_list_t* linphone_core_get_calls (   LinphoneCore *  lc  )   

The part I'm having trouble with is the const bctbx_list_t* return value. I tried declaring the dllimport like this:

<DllImport(LIBNAME, CallingConvention:=CallingConvention.Cdecl)>
Private Shared Function linphone_core_get_calls(lc As IntPtr) As List(Of IntPtr)
End Function

and then using it like this:

Dim CurrentCallList As List(Of IntPtr) = linphone_core_get_calls(_LinPhoneCore)

which compiles but gives me an error:

Cannot marshal 'return value': Generic types cannot be marshaled.

Any help would be greatly appreciated.

Answer 1

Based on GSerg's comment, I went looking for the definition of bctbx_list_t, which I found here. It's a linked list:

typedef struct _bctbx_list {
    struct _bctbx_list *next;
    struct _bctbx_list *prev;
    void *data;
} bctbx_list_t;

I translated that to:

Private Structure _bctbx_list
    Public [next] As IntPtr
    Public prev As IntPtr
    Public data As IntPtr
End Structure

changing the import to:

<DllImport(LIBNAME, CallingConvention:=CallingConvention.Cdecl)>
Private Shared Function linphone_core_get_calls(lc As IntPtr) As _bctbx_list
End Function

And I'm in business.