[wxPython-users] Re: Re: Sorted List Control - how?

[Robin Dunn]

Donn Ingle wrote:
>> A "callable object" doesn't have to be a class with a __call__ method.
>> It is anything that can be called, IOW, any foo for which foo(a,b) is
>> possible.
> Robin,
> If all that ca get passed to foo is a and b - which are numbers assigned
> during a SetItemData call, how can one achieve an alphabetical sort?

Because of the unfortunate decision made years ago to model the 
wxListCtrl API on the Win32 ListView API we are stuck with some a bad 
design issues until we have something that can replace the wxListCtrl. 
One of those is that each items' data value is what is passed to the 
sort function rather than something like the item indexes or whatever.

So the way to work with this wart, instead of against it, is to maintain 
something that will allow you to map from the item data value to the 
item or the item's textual values.  The Python dictionary is perfect for 
this, and is how it is done in the ListCtrl.py sample in the demo.  Then 
you simply have to assign each item a unique numerical value as a data 
value, and make that value a key in a dictionary that maps to the values 
or objects you want to use for sorting.  Then your sort function simply 
looks something like this:

def SortCompare(self, key1, key2):
	value1 = self.valueMap[key1]
	value2 = self.valueMap[key2]
	return cmp(value1, value2)

Of course you can use something besides a dictionary to get from the key 
to the value, if that makes more sense for your app.  Also if needed the 
comparison can be much more complex as well, for secondary sorts using 
values in other columns, etc.



> I mean - let's assume everything I put into the listctrl up-front gets the
> numbers 1 to 10 as the items go into it; later-on I want to add a new item.
> How do I know what number to give the new item such that it will sort into
> the listctrl? 
> Let's say the new item should fit between 3 and 4 in the list. How do I know
> this?

You don't need to know.  Just give it a new key value of 11 (or 
whatever) that maps to the sortable values, and then call SortItems 
again.  The key will get mapped to the text to sort by and the item will 
get shuffled into place.


-- 
Robin Dunn
Software Craftsman
http://wxPython.org  Java give you jitters?  Relax with wxPython!