[Qt-interest] QTableView::addColumn()

[Neel Basu]

On Monday 22 Dec 2008 9:02:51 pm Sebastian Fischer wrote:
> NOTE:  Sorry,  I had already sent this but for some reason it seems it
> never appeared on the list, so this is the next try...
> 
> on 20.12.2008 at 13:17 you wrote:
> > On Saturday 20 Dec 2008 5:05:03 pm Sebastian Fischer wrote:
> >> on 20.12.2008 at 10:50 you wrote:
> >> > Why there is no suchmethod like QTableView::addColumn() ?
> >> > in Model View architecture some data maynot come from model.
> >> > may be a check box or a edit button or a total, avg column that are
> >> > calculated by the data from other columns.
> >>
> >> That would be exactly something the model would do. If you want this
> >> just return +1 columns form the model (in case it's a custom model)
> >> and do your calculations there. If you have some other base model
> >> (like SQL or FileSystem and so on) create a simple proxy model that
> >> doesn't do anything but add that column (or allow users to dynamically
> >> add various sorts of sum columns and other stuff).
> 
> > Model means it delivers concrete data. 
> > when you are making a table suppose a marksheet table marks of subjects of
> > different students are the concrete values 
> > Total and avg are for representation and they are not going to take any place
> > on record or storage.
> > so they should not come from model.
> 
> These totals and averages are still concrete data, it doesn't matter
> if it can be calculated from other values. The view isn't suppsed to
> 'create' any data, even if it's just a modification of the raw data
> stored somewhere. The model also doesn't (necessarily) just provide
> acces to the data that is stored.
> The model should provide all data a view MIGHT need (including these
> calculated columns for example), the view can then pick which ones to
> display. That's why the Table/Tree views have the setColumnHidden
> functionality.
> 
> >> As  the  name  'View'  suggests,  it  doesn't do anything but show you
> >> content  (and  maybe  let  you  edit  it). Data storage / calculations
> >> should be done where the data belongs, in the model.
> >>
> >> > all this columns are not a part of model so there should be an
> >> > addColumn() method on view also so that data that are not coming from
> >> > model would not have any relation with model
> 
> > why would there be a representation specific overhead on model ??
> > When you are isolating view for representation all representation specific
> > things should go in View.
> > Both model and view might have calculation overhead.
> > but Model's calculation overhead should be limited to storage specific it
> > might also deal with data to deliver something else by conditional checking.
> > But it should never **CARE** for presentation layer.cause people can plug the
> > same model into different views where the are viewing the **SAME THING(model
> > data)** from different aspects/angles. and its not possible for a model to
> > forsee all this aspects/angles.
> > and view layer should always deal only with representation part and it should
> > be able to do calculations specific to representation.
> 
> That's  one  of  the  things  proxy  models  are  for  (at least to my
> understanding).  You use the same base-model for the (raw) data and if
> you have the need to adapt it for specific ways of viewing it, you put
> a proxy model in between, making the changes to the data for you (like
> adding  a column with sums of the other columns). Primarily sorting or
> filtering (which btw. is also no longer the raw data, and yet it's not
> the  view where you make these changes). Like mentioned above, in case
> you're  just  adding  a column that isn't even necessary since you can
> just hide it in views where it isn't needed/helpful.
> 
> I  know  all  this is to some degree a matter of taste, like where the
> line is drawn between models and views. At least for Qt it seems to be
> pretty  clear  from what capabilities the classes have that models are
> intended  to  do  everything  data-related  and the views only display
> them.  And  yes,  the views have sortingEnabled properties, they don't
> actually sort the data though, but relay it to the model (it's just to
> allow  you  to  set  the  sorted  column by clicking on the header and
> such).

However I've noticed that <Qt3 had addColumn() functions on Views thats why I was saying that they shouldalso be present in Q4
cause different people can entertain their different tastes.

Is it possible to make a custom View by subclassing AbstractItemView that lets me add one more Column on the View ?
Its just my flavour to remove such unnecessary calculation overhead from model and do it in View.