[Interest] QAbstractItemModel::headerData

william.crocker at analog.com william.crocker at analog.com
Mon Nov 25 13:37:57 CET 2013

On 11/22/2013 02:31 PM, andre at familiesomers.nl wrote:
> Bill Crocker schreef op 22.11.2013 20:19:
>> Gang:
>> I have created my own item model by sub-classing QAbstractItemModel.
>> Functions like rowCount take a parent index so the model
>> knows for which index it is being asked to return the count.
>> This is good.
>> My model is hierarchical and different points in the hierarchy
>> have a different number of rows and (especially) columns.
>> So, how come ::headerData is not passed an index so it knows for
>> which parent index it is being asked to return the data?
>> I'm using Qt 4.7.1
>> Bill
> Because Qt does not support vertical headers for tree models (check
> QTreeView, there is no vertical header there!) and it does not support
> different columns for child items either. While theoretically it should
> be possible (after all, QAbstractItemModel really models a nested grid),
> the views simply do not support it. There are 3rd party add-ons that
> provide more sophisticated views that can do this sort of thing, but the
> basic Qt model/view system can't handle that. Qt doesn't even handle
> cell spanning (QAbstractItemModel::span is not used.)

I have been using Qt for a while.
To work around this problem I sneak sufficient information into the
model so the ::headerData function can compute the current effective
root index. That has been working for years.

For the first time in my Qt history I am now trying to
position a QSortFilterProxyModel on top of my original model.
(For the record: You can have no confidence in your item model
  implementation until you have used it with a proxy model (and
  that includes models which have been vetted by modeltest.h))

Anyway, apparently I am still doing something wrong
because ::headerData is being called with a 'section' of -1.
I am not telling you this with much hope of help (the context
is too complicated for me to include a small example which
demonstrates the problem). Just mention me in your prayers.  :-)


> André
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