[Qt-interest] A design problem

[lists4pghanghas]

On Monday 03 May 2010 04:28 AM, hugh wrote:
> On Mon, 3 May 2010 05:27:30 am lists4pghanghas wrote:
>    
>> Hi
>>
>> I am having some design problems with my qt development. not to mention
>> I am new to Qt and OOP development. Here is one of them:
>> When I do implement subclasses for my particular use. I find it hard to
>> decide where to handle qt keypress events. Say I have a small gui
>> component that will need some drawable elements as its children and
>> sometimes the parent child hierarchy can go deeper. Now I am faced with
>> the task of choosing where to handle the key events, All in the ultimate
>> parent or with every element(leaving unhandled key event for its parent)
>> thus making them focusable (as a prerequisite) and everybody signals
>> there change in state or anything due to keys by emitting a signal, and
>> then that signal can be propagated upwards if required. But the second
>> approach sometime leads to chaining of signals if only the ultimate
>> parent is exposed to the rest of the application. eg child's signal
>> connected to its parents slot or signal, then parents signal connected
>> to its parents signal or slot ultimately reaching a stage where its
>> available to rest of the application as a whole.
>>
>> Thanks
>> PSG
>>
>>      
> Hi PSG,
> I spent many years doing OO development under Windows, and this was always a
> problem to me.  In the end I decided that sometimes it is better to handle the
> signal at the top level widget, but at other times to handle it at the specific
> widget/control.
>
> When you talk about the parent and child widgets, I hope you are talking about
> widgets within other widget on the dialog/panel/top level widget.  This is not
> a matter for C++ inheritance!  I found it best to keep the number of widgets
> within widgets small, that is what I would call a flat structure.  This reduces
> the number of "generations" of parent/child in your layout.
>
> Whichever way you do this you will need to either pass the signals up, or down
> the structure.   Encapsulation is an OO concept where, in this case you try to
> reduce how many other widgets need to be signalled when a particular event
> happens.
>
> I had a number of widgets that were used in many places, and for these it was
> easier to have them do the processing, as it made placing them in new layouts
> easier.
>
> I hope I have not confused you.
>
> I guess the important thing is are you sure you need so deep a structure,
> because that is why you have the long chains of signal/slots.
>
> H
>
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>    
Thanks Hugh,

Till now I was under the impression that "deeper structure give one 
better design and reusability, trying to make every small and large 
item/widget independent and reusable". But I guess I was wrong. Its not 
always worth the trouble. I will try to keep the structure flatter this 
time and lets see how it turns out.

PSG
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