QTreeView details: what are viewItems?

[anda_skoa]

The d-pointer idiom is used to keep the public API of QTreeView binary stable while still having the option of adding/removing/renaming functions necessary for the view's procesing.

The d-pointer points to a private class that holds the actual implementation of the view, often also referred to as PIMPL idiom (pointer to implementation).

The Q_D() and Q_Q() macros enable const correct access to the private and public class respectively.

The class you are looking for ist QTreeViewPrivate

Cheers,
_

[neuronet]

The d-pointer idiom is used to keep the public API of QTreeView binary stable while still having the option of adding/removing/renaming functions necessary for the view's procesing.

The d-pointer points to a private class that holds the actual implementation of the view, often also referred to as PIMPL idiom (pointer to implementation).

The Q_D() and Q_Q() macros enable const correct access to the private and public class respectively.

The class you are looking for ist QTreeViewPrivate

Cheers,
_

Thanks I will ruck about see what I figure out and post here.

[ChrisW67]

Within the Qt source the private implementation is usually in a file named blah_p.h for a class blah with its public API in blah.h. The private header is #included into the implementation file blah.cpp but not inthe public header or user programs.

I would not worry too much about the internals of the views and models if all you want to do is use them.

[neuronet]

Within the Qt source the private implementation is usually in a file named blah_p.h for a class blah with its public API in blah.h. The private header is #included into the implementation file blah.cpp but not inthe public header or user programs.

I would not worry too much about the internals of the views and models if all you want to do is use them.

Thanks a lot for the specifics, that is helpful, though I am frankly still a bit lost.

tl;dr : Good point: my goal is just to use this software, not become a developer. If it really is important I learn the internals, I will need to learn Qt for real (c++).

The problem is, as I try to explain to other PySide users what is going on underneath, I often have no idea. For instance "Why the redundancy between model.data() and index.data(): why not always use one or the other?" It is frustrating to not be able to go in and figure such things out easily on my own. c++ code is a labyrinthine mystery to me for the most part. For some things, going to the source is really helpful. With QTreeView, it has been mostly frustrating.

[anda_skoa]

QModelIndex::data() is for convenience, in case you want to retrieve data pointed to by a QModelIndex.

But the data retrieval function has to be implemented somewhere and since one cannot "inject" something into QModelIndex, the next possible place is the model.

So QModelIndex::data() can then always be just a simple indirection

QVariant QModelIndex::data(int role) const
{
    model()->data(*this, role),
}

QVariant QModelIndex::data(int role) const
{
    model()->data(*this, role),
}

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Cheers,
_

[neuronet]

I found a great Doxygen resource for navigating Qt (unfortunately only up to 4.2 I couldn't find any doxygenated 4.8: if anyone has a link let me know...).

Using it made navigating the c++ code much easier, and the code seems largely the same as in 4.8, so I've been using the doxygen pages (for 4.2) to find stuff in 4.8. For instance, the documentation for qtreeview_p.h has the following useful bit:

QVector<QTreeViewItem> QTreeViewPrivate::viewItems [mutable]
Definition at line 134 of file qtreeview_p.h.

Cool, we have a QVector of QTreeViewItems, and this is the mysterious viewItems that I was asking about! Many of the viewItems methods were actually just QVector methods, and part of my confusion is that QVector is not part of PySide.

At any rate, in 4.8, on line 178), we see the relevant line:

mutable QVector<QTreeViewItem> viewItems;

mutable QVector<QTreeViewItem> viewItems;

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So we have a vector of QTreeViewItem types, and QTreeViewItem has its own page here. But more importantly, qtreeviewitem is the first structure defined in qtreeview_p.h! In terms of clues about when it is being populated, check line 2495 of qtreeview.cpp (d->viewItems.insert(insertPos, delta, insertedItems.at(0))). Where 'insert' seems to be a built-in method for QVectors.

This seems like a very promising line of attack for other Python users (perhaps future me) to insinuate themselves into this often baffling code.