Re: custom TreeModel

[Tamer Mowafy <kalimakhus yahoo com>]

Jonathon

I have enjoyed following the discussion about
introducing a generic TreeModel class. Using a
template class is a great idea for it sure would make
it easy to initialize the class with STL containers. I
have some few notes
first if the basic idea was to keep only one copy of
data around, you may think of using a reference to the
wrapped container.

>private:
> T m_container;
can be:
T& m_container;

this will allow two-way updates to be automatically
sensed on both the view and model sides.

Second you may consider declaring your template
parameters like this:

template < class T, template < class U, class =
allocator <U> > class TContainer>

this makes your class instantiated with both the
container and the type it is storing. I just guess
that this may come handy later on.
In this case the member variable should look like
this:
TContainer<T>&  m_container;

Another approach that should make your implementation
more generic, is to use iterators to initialize the
class rather than a whole container. This would allow
the class to accept a wider range of containers (even
arrays and pointers). Though this can be problematic,
(After thinking this won't work for the purpose at
hand).

Last point is the question, should the user inherit
from your class or not? Well, it is there and it has
virtual functions and some will do so even if you
provided some other alternative. Still for the sake of
better view/model separation it should be better that
they don't. You will still need to acquire columns'
values from the user as well as communicating back the
mutations performed on these values through the UI.
One way to do that is to use some helper class let's
say ValuesProvider. The user can inherit from it and
supply a pointer/reference to your class that can call
the helpers functions to get values for each row of
data (or each column individually) as this is needed.
It can pass an iterator over the container. If you
have a reference to the container rather than a copy
such iterators will be valid ones. By the way this
approach is used in the java API of eclipse namely in
the jface package.
Some other approach is to use signals that the user
can connect to and supply column values through his
slots. 
In both cases you should use a generic type to receive
the values which would be Glib::ValueBase since it is
catually the type used in the vfunc in your class
anyway.

I hope these notes are not totally out of point.

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