[Interest] Proper way of updating a model?

[André Somers]

Op 22-8-2012 20:29, Stephen Chu schreef:
> Now I have a question on how to properly update the model. My model is a
> read-only representation of a database. I am using a QTreeView to hold
> the model. The data themselves are not tree-like but I like the visual
> of QTreeView better.
So, you *do* have a table model, but you are just displaying it in a 
QTreeView? That's very possible, of course. Note that QTableView can be 
given the same appearance as QTreeView, but is more efficient at 
layouting because it does not need to deal with the (complex) tree 
aspects of it.

Please keep in mind that *any* model can in principle be viewed in *any* 
view. You may loose certain aspects of the data of not use all features 
of the view, but normally, it will work. That's because views only rely 
on the common interface provided by QAbstractItemModel.
> The model needs to update itself periodically from the remote database.
> I keep a QList of data IDs and rebuild the list every time I get a new
> snapshot from the database.
For efficient updating, you will need to keep track of changes: inserts, 
deletes and updates of items. Just rebuilding will generally not be very 
efficient.
>
> What's the recommended way to reflect the changes to the view? I need to
> keep the current selection and scroll position of the QTreeView between
> updates.
>
> Do I reset the model? Or do I remove deleted rows and insert new ones?
No, resetting is not the way. It will result in loosing selection, 
scroll position and is generally visually disturbing for the user. As 
others have notices, the beginInsertRows, beginRemoveRows and their 
respective end* functions are your tools, together with emitting the 
dataChanged signal for updates to data.

However, it also depends on the size of your dataset. Are you talking 10 
rows, 1k, 1M or even more?

André