[Qt-interest] FW: QAbstractItemModel: Hiding rows

[Arnold Krille]

Hi,

On Thursday 09 July 2009 22:46:51 Eric Clark wrote:
> This is not "simply" a removal of rows. My model is setup to get its
> information from a hierarchial tree structure already defined by a
> different object in my application. The other object always has these items
> in its list of children, no matter if they are hidden or not. The "hidden"
> part is only a GUI preference because some of the objects are not to be
> shown in the TreeView, but they are still there. Removing the rows would
> cause very bad bugs, since the rowCount always returns the number of
> children and the ability to get a child by row number would be screwed up
> because I would have to index things based on their visibility, not their
> existence in the children array. Not exposing it via the model is not an
> option as that would make my life very difficult. I would have to reorder
> indexes all the time, and have to have lots of extra code.

So actually your model is already a proxy to the real data:-) And all you want 
to know is what method of hiding some data from the proxies is least costly. 
As I said, either 1) hide it directly in your model (yes, that involves index-
reordering) or 2) do it via a proxymodel (yes, that involves index-
reordering)...

The model-view concept is actualy working like this: The views show everything 
exported by the model. And its the models responsibility to hide what is not 
to be shown.

If you try to introduce a new role, you also have to implement your own 
views/delegates to be used with your model. And that is counter-productive. 
The advantage of the model-view-pattern is that (almost) all views can display 
the data given in the model. Some my not look interesting (imagine a chart-
view coupled to a QDirModel:), but all work without modifications or big 
specializations.

Have fun,

Arnold
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