QTreeView from QListView from QAbstractListModel

[JonB]

I'll try to keep this brief, as often I type in a lot, and then I don't get much response and I get sad/frustrated :(

I need seem encouragement/putting on the right path/allaying of fears.

Presently we have a JSON file with a flat list of records, which have a number of arbitrary attributes/fields/columns:

[
  {
    ...,
    ...,
  },
  {
    ...,
    ...,
  },
  ...
]

[We have a class for the rows ultimately derived from QAbstractListModel. I see that the whole element row with its columns/fields (i.e. class instance) is dumped into a single self._data[index.row()] = value. This architecture is not to be changed. I don't think this is relevant. Sorry for the digression. I'm learning as I go. So we have a list model with blobs for the items.]

At present this is a displayed in a QListView. A data item presents some field in its blob for the list item label. That's fine.

Now we want to change this a bit. The JSON items will be nested inside "categories", like:

[
  { category1,
    [ {item1}, {item2}, ... ]
  },
  { category2,
    [ {item3}, {item4}, {item5}, ... ]
  },
]

We want to present this to the user in a QTreeView, so that user can see items nested inside categories/sections.

But QAbstractListModel, and for that matter QAbstractTableModel, admonishes me:

Since the model provides a more specialized interface than QAbstractItemModel, it is not suitable for use with tree views [although it can be used to provide data to a QListView]; you will need to subclass QAbstractItemModel if you want to provide a model for that purpose.

But I'm stuck with a model which is already derived from QAbstractListModel... :(

I'm trying to get my (sore) head around what's going on here, and how I can proceed. I guess the issue is that the present list model --- whose elements' class is shared with other areas of code -- doesn't have any ability for parentage, that's why I can't treeview-ise it?

What model type are you supposed to put a QTreeView on? If a QListView can use a QAbstractListModel, where is/why isn't there a QAbstractTreeModel class for a QTreeView?

Is there any way I can force a square-peg QAbstractListModel into a round-hole QTreeView? :) Or a different widget if, say, I stipulated there will only ever be 2 levels: categories/sections at the top with a list of leaves as children?

Like, say, in Qt Designer, the left-hand pane contains a list of widgets to drag from, just like we have at present, but it divides them up into categories/sections (Layouts, Spacers, ...) to help the user, that's just what we want.

I think someone called in an "accordion". (Is it an available Qt widget??) But I guess although the selectable items are a list, in order to categorise/section/group the "data model" cannot be just a list, it has to have "parentage" for the sections too?

[SGaist]

Hi,

Not a direct answer but are you looking for something like the QJsonModel project ?

Beside that you have the Simple Tree Model example that should give you a good overview of what is needed to write a tree model.

[JonB]

@SGaist
Thanks for that, especially the simple tree model as a sample.

Not surprisngly, a quick search on that page shows they are using

class TreeModel : public QAbstractItemModel

and similarly class QJsonModel(QtCore.QAbstractItemModel) for the JSON.

But I am saying the model I'm given is already a QAbstractListModel --- note the List --- and it is used as such elsewhere in other code. So changing it will be problematic. Hence I want an idea for "square-peg into round-hole" ;-)

I don't imagine that will be forthcoming!

Meanwhile, that "accordion" widget I show in my pic from Qt Creator/Designer, do you know if that is available as a Qt widget??

[SGaist]

Maybe a custom proxy model on top of it ?

As for the widget, it's a QToolBox

[JonB]

@SGaist

Maybe a custom proxy model on top of it ?

Yes, I wondered about that.

As for the widget, it's a QToolBox

Oohh! I wish the man page showed a pic of it, but if you say so. So that does not use a model/view. Ah, I see it doesn't hold my leaves, I have to split them up into what the "tabs" are.

But QToolbox has a "current item", and I don't see it supporting expanding or contracting each tab separately. It's more like a QTabbedWidget for showing one tab at a time? That's not what the Qt toolbox is doing, is it? What tab/item is the "current" one? There isn't such a thing. Where is the expanding/contracting provided from? What single widget type are they using for each tab content? It might be derived via a QToolbox, but did they have to write all that functionality?

[SGaist]

The current item is the widget shown under the "tab".

You can put a QListView in there to show what you want.

[JonB]

@SGaist
I'm obviously not getting it, because I thought the "current item" was the current tab, like on a QTabWidget. The docs don't mention anything about expanding/contracting of the tabs, clicking on the expander icon at the left, which seems odd to me, as there should be an expand/contract signal etc. I guess I'll need to try it out to understand!

[SGaist]

The name might be a bit misleading. The item is indeed similar to the tab of the QTabWidget.

[JonB]

@SGaist
This may be moot now, as my stakeholder has decided he wants the data to be visually presented in a QTreeView rather than a QToolbox. However it was good to learn about that widget, I may check itout just to look at it but not sure now :)