[Interest] Example for: QTreeView + QAbstractItemModel + external data

Björn Schäpers qt-maillist at hazardy.de
Wed Apr 27 23:45:42 CEST 2016

Am 26.04.2016 um 19:05 schrieb anton:
> Hi,
> I have subclassed QAbstractItemModel,
> and I want to load additionally data in the model
> as soon as somebody clicks on the [+]
> in the treeview to load the children of this
> item form an external data ( web- app which gives me json data back).
> Now:
>   I reimplemented hasChildren() in the model
> but i am not sure about the moment to load the data.
> I suppose that the rowCount() method of the model is called
> when somebody expands an item in the view?
> If not what is the moment when my model should ask for additional Data?
> Does there exist a small example which demonstrates how to
> handle this in an optimal way.
> Not sure about beginInsertRows() or layoutChanged() ..
> I am experimenting but i get also some crashes so an
> example project would be nice.
> Thanks
> Anton
I think you are looking for QAbstractItemModel::canFetchMore() and fetchMore(). 
See also the last paragraph in http://doc.qt.io/qt-5/qabstractitemmodel.html

To create models that populate incrementally, you can reimplement fetchMore() 
and canFetchMore(). If the reimplementation of fetchMore() adds rows to the 
model, beginInsertRows() and endInsertRows() must be called.

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