How do I deal with multiple common user interfaces?

Question

I'm working on a python application that runs on 2 different platforms, namely regular desktop linux and Maemo 4. We use PyGTK on both platforms but on Maemo there are a bunch of little tweaks to make it look nice which are implemented as follows:

if util.platform.MAEMO:
    # do something fancy for maemo
else:
    # regular pygtk

There are roughly 15 of these if statements needed to get the UI looking and working nice on Maemo 4.

This has been very manageable for all this time. The problem is that a while ago there was a new version of Maemo released (5, aka fremantle) and it has some big differences compared to Maemo 4. I don't want to add a bunch of checks throughout the GUI code in order to get all 3 platforms working nicely with the same codebase because that would get messy. I also don't want to create a copy of the original GUI code for each platform and simply modify it for the specific platform (I'd like to re-use as much code as possible).

So, what are ways to have slightly different UIs for different platforms which are based on the same core UI code? I don't think this is a python or Maemo-specific question, I'd just like to know how this is done.

Answer 1

You could isolate the platform specific stuff you need to do into small consistently named functions inside a platform module, create the right function name using the platform you're running on and then getattr the right one and call it. The if/else boilerplate would disappear then.

Answer 2

You could wind up much of this in a factory:

def createSpec():
  if util.platform.MAEMO: return Maemo4Spec()
  elif util.platform.MAEMO5: return Maemo5Spec()
  return StandardPyGTKSpec()

Then, somewhere early in your code, you just call that factory:

 spec = createSpec()

Now, everywhere else you had conditions, you just call the necessary function:

 spec.drawComboBox()

As long as drawComboBox(), handles anything specific to the platform, you should be in good shape.

Answer 3

I've made a separate module to handle all of my specializing between normal Linux, Maemo 4.1, and Maemo 5. It detects what features are available and allows the program to gracefully degrade.

For example

 def _fremantle_hildonize_window(app, window):
         oldWindow = window
         newWindow = hildon.StackableWindow()
         oldWindow.get_child().reparent(newWindow)
         app.add_window(newWindow)
         return newWindow


 def _hildon_hildonize_window(app, window):
         oldWindow = window
         newWindow = hildon.Window()
         oldWindow.get_child().reparent(newWindow)
         app.add_window(newWindow)
         return newWindow


 def _null_hildonize_window(app, window):
         return window


 try:
         hildon.StackableWindow
         hildonize_window = _fremantle_hildonize_window
 except AttributeError:
         try:
                 hildon.Window
                 hildonize_window = _hildon_hildonize_window
         except AttributeError:
                 hildonize_window = _null_hildonize_window

For more, see Dialcentral, Gonert, ejpi, or Quicknote's source code for a file called hildonize.py https://garage.maemo.org/plugins/ggit/browse.php/?p=gc-dialer;a=blob;f=src/hildonize.py;

Another example from The One Ring's GObject Utils (go_utils.py)

 def _old_timeout_add_seconds(timeout, callback):
         return gobject.timeout_add(timeout * 1000, callback)


 def _timeout_add_seconds(timeout, callback):
         return gobject.timeout_add_seconds(timeout, callback)


 try:
         gobject.timeout_add_seconds
         timeout_add_seconds = _timeout_add_seconds
 except AttributeError:
         timeout_add_seconds = _old_timeout_add_seconds