Using aggregate/accessors

[yrs90]

On accessing items:
I tried the following code. Too bad, I can't create a debug build and use a
debugger.

wxListCtrl *pList = wxDynamicCast(event.GetEventObject(), wxListCtrl);
aggregate ag(make_aggregate(*pList));
accessor ac(ag["Items"]);

if (ac.is_valid() && ac.is_container())
{
container c = ac.get_container();

// yeah, it worked... etc.
}
else if(ac.is_valid() && ac.is_aggregate())
{
wxMessageBox("is an aggregate");
}
else if(ac.is_valid())
{
wxMessageBox("valid but not a container");
}
else
{
wxMessageBox("not valid");
}

This code returns 'valid but not a container'. Before I put the
is_container() check in, it generated a runtime error.

In a separate problem, I added a constructor/destructor to an otherwise
unchanged class that I pass to the framework and suddenly I started getting
runtime access violations. Is there some type of change to the ADAPTER
declaration required when there is a constructor in the class? I'll send
additional details if the answer solution isn't immediately apparent.

Best regards,
Joel



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[Hajo Kirchhoff]

Post by yrs90
This code returns 'valid but not a container'. Before I put the
is_container() check in, it generated a runtime error.

What do you pass to "Items"?

Post by yrs90
In a separate problem, I added a constructor/destructor to an otherwise
unchanged class that I pass to the framework and suddenly I started getting
runtime access violations. Is there some type of change to the ADAPTER
declaration required when there is a constructor in the class?

No requirements for adding a constructor/destructor. Must be a problem
on your side. Have you tried rebuilding?

BTW, you will get lost very quickly without a debugger. If you cannot
afford the Visual Studio Standard edition and if you are adventureous
you could download the visual studio .NET 2005 C++ Express version and
use that debugger there (I think it has one). It should be able to debug
code generated by the free MS tools, provided the free tools let you
switch on debugging information.

Not having a debugger is not really an option IMHO for something so new
as the lit window library.

Best regards

Hajo



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[yrs90]

Post by Hajo Kirchhoff

Post by yrs90
This code returns 'valid but not a container'. Before I put the
is_container() check in, it generated a runtime error.

What do you pass to "Items"?

I am passing a vector<class MyListData> to Items.

Specifically,

RULE("xrcMainList.Items", make_expr<accessor>("m_ListData"))

Where
vector<MyListData> m_ListData;

BEGIN_ADAPTER(DataClass)
PROP(m_ListData)
END_ADAPTER()

IMPLEMENT_ADAPTER_CONTAINER(vector<MyListData>)

At least, m_items.is_container() == true, because the FillList() function is
populating the wxListCtrl and it only populates the list if
m_items.is_container() is true.

Post by Hajo Kirchhoff
No requirements for adding a constructor/destructor. Must be a problem
on your side. Have you tried rebuilding?

Yes I made sure to do a clean rebuild. I'll look at it more closely after I
get further along.

Post by Hajo Kirchhoff
Not having a debugger is not really an option IMHO for something so new
as the lit window library.

Yes, I agree. I only have this problem building debug versions if I use
LitWindow and consequently STL. Using a debugger is possible as it is, but
it is quite tedious to use without symbol tables. Unfortunately I have to
factor in the cost of buying new tools for a couple of C-runtime libraries
into the decision about whether to commit to using LitWindow. I'll take a
look at the VC 2005 Express Beta to see if that will resolve the immediate
need.

Thanks,
Joel




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[yrs90]

Post by Hajo Kirchhoff
No requirements for adding a constructor/destructor. Must be a problem
on your side.

Ah, found it. Indeed a problem on my side. In my constructor I called an
internal clear function in which I call NotifyChanged(). :/ Obviously, it
is hard to notify a half-constructed object.

Thanks,
Joel



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[Hajo Kirchhoff]

Hi,

Post by yrs90

Post by Hajo Kirchhoff
What do you pass to "Items"?

I am passing a vector<class MyListData> to Items.
Specifically,
RULE("xrcMainList.Items", make_expr<accessor>("m_ListData"))

ah, of course. Tiny detail, big effect. I didn't pay close enough
attention. You are not passing a vector<>, you are passing an accessor
to a vector. Thats the same difference between Type and Type*. The
accessor is like Type*. You need to dereference the accessor to get to
the vector.

On the wxListCtrl side:

Items is not a vector<MyListData>, its an accessor, which in your
situation currently happens to point at a vector<MyListData> but could
point to a totally different data type a few microseconds later.

So you have

wxListCtrl *pList = wxDynamicCast(event.GetEventObject(), wxListCtrl);
aggregate ag(make_aggregate(*pList));
accessor ac(ag["Items"]);

ag["Items"] returns an accessor to the property. If the property is of
type long, it returns an accessor to a long object. If the property is
of type string, it returns an accessor to a string object.
In your case, the property is an accessor, so ag["Items"] returns an
accessor to an accessor object.

To get to the real accessor, the one you are interested in, you must
dereference the accessor, much like *ag["Items"].

But accessors are untyped objects, so you need to cast it into a typed
accessor first, then dereference it. Here is how:

typed_accessor tac=dynamic_cast_accessor<accessor>(ac);
accessor the_real_items_accessor=tac.get(); // this is like '*ac'
the_real_items_accessor.is_container()==true;




I'll rewrite the scenario using pseudo-code and replace accessor with
'void*' to make things more clear.

wxListCtrl *pList=wxDynamicCast...
aggregate ag(make_aggregate(*pList));

// ag["Items"] returns a void* to the "Items" member property
// which is itself of type void*
// so ag["Items"] return type is void **
void **ac=ag["Items"]; // ag.Items

// cast it so we can get to the data

void *tac=*(void*)ac;
vector<MyDataStruct> *the_real_items_accessor=(vector<...>*)tac;



***
Here is the full version again, that should work now:

wxListCtrl *pList = wxDynamicCast(event.GetEventObject(), wxListCtrl);
aggregate ag(make_aggregate(*pList));
accessor ac(ag["Items"]);

typed_accessor tac=dynamic_cast_accessor<accessor>(ac);
accessor the_real_items=tac.get();

if (the_real_items.is_valid() && the_real_items.is_container())


Looks more complicated than it is until you think of accessors as void*
pointers with type information, which is exactly what they are by the way :)


Hajo



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