ui factory - what should it do?

[John Arbash Meinel]

Martin Pool wrote:
> On Tue, 2006-02-21 at 17:05 -0800, Robey Pointer wrote:
> 
>> The code I posted last week used a single pbar object, on which  
>> callers could push and pop state.  Debouncing is trivial that way.   
>> We could also use weakref to do an automatic pop when a child pbar is  
>> collected (though I may be jumping ahead here).
> 
> Probably better to just have code use a try/finally block in the scope
> where the progressbar is created.
> 


The way I did it was to have 1 object which was responsible for updating
the screen (CallbackHandler). It had a function called 'new_progress'
which would return a Progress object. these objects had a member called
"new_sub_progress" which would return another Progress object.

The current state was a tree (list of lists) of ProgressInfo objects. So
when new_sub_progress() created a new Progress, it would create a
ProgressInfo, append it to its list. Instantiate the child Progress with
this info object, a pointer to self, and a pointer to CallbackHandler.

So children know about their parents, but parents only know about their
child's current state.

All Progress objects have a 'done()' member, but this is also called in
their __del__.

When a Progress is updated, it does:
  self.info.position += 1
  self.cb_handler.update()

Where CallbackHandler.update() traverses the tree, and figures out what
should be displayed.

This avoids cyclical references, and I've seen that it works fairly
well. If you have 'try/finally' you can force a '.done()' command.

My code mixes C++ with python, so I don't always have a finally. And my
code is such that I have an abstract Progress object, which has a very
fast inline 'update()' function, which occasionally calls a virtual
'do_update' function.

John
=:->


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