[Qt-interest] QTreeView and custom QAbstractItemModel performance problem

[Andreas Pakulat]

On 08.07.10 10:14:11, Felix Brack wrote:
> Hello,
> 
> By subclassing QAbstractItemModel I have create a custom model that 
> stores data from a communication trace row by row. Every row has 
> multiple columns such as a time stamp, the data traced from the 
> communication, etc. The number of rows in the data model is limited, 
> let's say to 100 rows. When adding row 101 it is appended and the first 
> row (i.e. the one with the oldest data) is removed.
> 
> To show the information to the user I use a QTreeView which shows each 
> row of the data in the model line by line, i.e. the model is not 
> hierarchic, all rows have the same parent (root) and consist of multiple 
> columns.
> 
> Things are working so far but performance is very poor and the CPU load 
> is incredible (even with just 100 rows). The reason for this is that 
> whenever I append a row to the model the view calls the models 'data' 
> member for all rows and all columns.
> 
> It seems that I'm missing something fundamental here and that appending 
> a row of data to my model looks for the view like the entire data has 
> changed. I will have to change something so only the data from the newly 
> append row is queried by the view.
> 
> I just don't know how to do that... Can anybody push me into the right 
> direction?

Can you post your model implementation? It sure sounds like you're doing
the appending wrong, but without having a look at the code its not possible
to say what exactly is wrong.

A blind guess could be that you're reset'ting you're model every time you
add a row instead of using begin/endInsertRows correctly. See the example
models in Qt.

Also I'd suggest to use a QTableView instead of QTreeView as that one is
significantly faster on non-tree structures (you can tweak it to have no
lines etc.) in case you ever get more than 100 rows.

Andreas

-- 
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