[wxPython-users] wxPython and MVC

[Pan Xingzhi]

Mark,

    Normally people regard things like wx widgets and web pages as view.
What you're doing is adding another abstract layer between controller and
view (the 'view' data member in the controller object), so ideally you may
change the view without affecting the controller. However, in most cases the
controller is allowed to be coupled with view (maybe except for the web
development, where view and controller may not even reside on the same
machine). Think about this: even if you apply the 'view' data member, you
still have to modify it if you change the UI from wx to web. So is it really
necessary to encapsulate this modification in this 'view' data member rather
than just modifying the controller?

    That depends on how much you need on changing the face of your software
;-) But my suggestion is, don't overdo it. A lot of people tend to invent
"imaginary requirement" and then find themselves devoting 80% effort on 20%
(or less) of the functionalities.

    You don't even need to make controller an object. Python doesn't force
this, neither does wx. In my opinion, a set of functions in a Python module
is enough. My point is that, the controller rarely has its own state, and
its job is to manipulate model and view rather than providing APIs to change
itself. OO gains little benefits here.

Cheers,
    Harry Pan

2007/12/3, Mark Erbaugh <mark at microenh.com>:
>
> On Mon, 2007-12-03 at 11:32 +0800, Pan Xingzhi wrote:
> > Hi Mark,
> >
> >     The controller must know something about the view, so it can
> > update the view according to the model.
> >     However I'm not sure with the "stub" thing you wrote. What's the
> > good out of that? Why can't we just bind some function in the
> > controller as event handlers?
> >
> > Cheers,
> >     Harry Pan
> >
> > 2007/12/3, Mark Erbaugh <mark at microenh.com>:
> >         I'm trying to develop applications along the lines of
> >         model-view-controller design.
> >
> >         I think the frame class is the view portion. However, the
> >         event handling
> >         routines are part of the controller.  How do people separate
> >         them?
> >
> >         What I've been doing is writing "stub" event handlers for each
> >         event
> >         that basically just pass the event off to a controller object,
> >         if one
> >         exists.
> >
> >
> >         # in view
> >         def onClick(self, event):
> >             if self.controller:
> >                 self.controller.onClick(self, event)
> >
> >         # in controller
> >         def onClick(self, view, event):
> >             # here view gives the controller access to the view object
> >             # (GUI frame instance)
> >
> >         Is there a better way?
> >
> >         Also, my concept of the controller is that it is independent
> >         of the
> >         mechanism used to provide the GUI, so I don't want to import
> >         wx into it.
> >         That means that sometimes end up writing more code in the GUI.
> >         For
> >         example, if the controller needs to display a dialog box, I
> >         have a
> >         method in the GUI frame to do that. The controller can then
> >         access the
> >         dialog using this method on the GUI frame. It gets the GUI
> >         frame's
> >         instance as the first parameter of its event handling code.
> >
> >         Thanks,
> >         Mark
>
> Harry,
>
> Thanks for the reply.  After reading more about wxPython event handling,
> I'm experimenting with that approach now and it looks like it may work.
> I agree that the controller will have to know something about the view
> so I added a 'view' data member to the controller object.  However, the
> controller object only accesses specific methods in the view object, it
> doesn't directly access wxPython features.
>
> For example, to populate a wxListBox, the controller would call a method
> view.setListBox(data).  The method in the view class would then call the
> appropriate wxPython method (or methods) to populate the list box.
>
> This way, if I would ever use a different GUI object, such as a
> web-based interface, it would only have to implment a setListBox(data)
> method and I could use the same controller.  Ideally, the same program
> could run with a desktop interface with wxPython, or even Tkinter) or a
> web-based interface.
>
> Mark
>
>
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