On Mon, Sep 15, 2008 at 9:37 PM, Georg Altmann <george@georg e-net.dewrote:
Well, I think one of the assumptions of the MVC is that the view can
be notified about the changes in the model. According to your
interface, the View can just be notified on operations about the
*whole* model, like adding or removing elements from it.
But the elements of your list-like class should be a part of your
model, and therefore should be able to notify the Views by
themselfves.
Just my 0,02 Euros.
Regards
Marco
--
Marco Bizzarri
Hello,
>
I need some advice on how to implement model-view-controller. I am trying to
develop a GUI application with PyQt, yet the problem rather applies to mvc
in general, not just GUI applications.
>
Let's say the data is a list of objects with a common base class. The views
are either a graphical representation of the objects or some form of textual
input. The views shall change the model by using command objects (for undo,
e.g. QUndoCommand).
>
My current approach is to implement the model as a class with a list-like
interface, with methods insert(), remove(), __getitem__(), __setitem__(),. ..
and a signal to notify the views. The objects in the list have methods to
change their state as well.
>
My problem is, how do the commands interact with the model?
Let's say I have a command that modifies an object o in the list.
>
1) If list[key_to_o] returns a reference to the object, the command can
modify the object by using this reference, i.e. list[key_to_o].setX(). So
there is no way for the list to know when the object changed - how can it
emit a singal then?
>
2) If list[key_to_o] returns a deep copy of the object,
copy_of_o = list[key_to_o], the command mofifies the copy and the updates
the list: list[key_to_o] = copy_of_o. Now the list can emit a signal in
__setitem__().
While this may work, it seems awkward to copy around objects just to perform
a possibly simple operation on them. Additionally it might not be feasible
once objects get complex.
>
3) The interface of the classes of the objects could be reflected in the
list class, i.e. list.set_x_on_o bj(key_to_obj,x ). This would probably make
the list class interface very bloated.
>
Of course the problem is not really limited to Python, my apologies if I'm
totally off-topic here.
>
Regards
Georg
>
>
I need some advice on how to implement model-view-controller. I am trying to
develop a GUI application with PyQt, yet the problem rather applies to mvc
in general, not just GUI applications.
>
Let's say the data is a list of objects with a common base class. The views
are either a graphical representation of the objects or some form of textual
input. The views shall change the model by using command objects (for undo,
e.g. QUndoCommand).
>
My current approach is to implement the model as a class with a list-like
interface, with methods insert(), remove(), __getitem__(), __setitem__(),. ..
and a signal to notify the views. The objects in the list have methods to
change their state as well.
>
My problem is, how do the commands interact with the model?
Let's say I have a command that modifies an object o in the list.
>
1) If list[key_to_o] returns a reference to the object, the command can
modify the object by using this reference, i.e. list[key_to_o].setX(). So
there is no way for the list to know when the object changed - how can it
emit a singal then?
>
2) If list[key_to_o] returns a deep copy of the object,
copy_of_o = list[key_to_o], the command mofifies the copy and the updates
the list: list[key_to_o] = copy_of_o. Now the list can emit a signal in
__setitem__().
While this may work, it seems awkward to copy around objects just to perform
a possibly simple operation on them. Additionally it might not be feasible
once objects get complex.
>
3) The interface of the classes of the objects could be reflected in the
list class, i.e. list.set_x_on_o bj(key_to_obj,x ). This would probably make
the list class interface very bloated.
>
Of course the problem is not really limited to Python, my apologies if I'm
totally off-topic here.
>
Regards
Georg
>
be notified about the changes in the model. According to your
interface, the View can just be notified on operations about the
*whole* model, like adding or removing elements from it.
But the elements of your list-like class should be a part of your
model, and therefore should be able to notify the Views by
themselfves.
Just my 0,02 Euros.
Regards
Marco
--
Marco Bizzarri
