Smarter way to get a list of children in Tree Model

[VRonin]

Hi guys, I'm being lazy here. Do you know of any Proxy model that shows only a certain level of a tree as a list?

What I need is to turn something like

• Item 1
  • Item 2
  • Item 3
• Item 4
  • Item 5

into:
when level property is 0

• Item 1
• Item 4

when level property is 1

• Item 2
• Item 3
• Item 5

I achieved it already using 3 proxies concatenated but wanted to know if there is a 1 proxy way already available.

My current solution:

#include <QIdentityProxyModel>

class LevelDataProxy : public QIdentityProxyModel
{
    Q_OBJECT

public:
    explicit LevelDataProxy(QObject *parent = nullptr) : QIdentityProxyModel(parent) {}
    enum {
        LevelDataRole = 1989
    };
    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override{
    if (index.isValid() && role == LevelDataRole) {
        Q_ASSERT(checkIndex(index));
        int result = 0;
        for (QModelIndex cursor(index); cursor.parent().isValid(); cursor = cursor.parent(), ++result) {}
        return result;
    }
    return QIdentityProxyModel::data(index, role);
}
};

and then I use it and a QSortFilterProxyModel with a KDescendantsProxyModel in the middle:

    // QAbstractItemModel* originalModel;
    LevelDataProxy* levelInfoProxy = new LevelDataProxy(&printSettingDialog);
    levelInfoProxy->setSourceModel(originalModel);
    KDescendantsProxyModel* flatModel = new KDescendantsProxyModel(&printSettingDialog);
    flatModel->setSourceModel(levelInfoProxy);
    flatModel->setDisplayAncestorData(false);
    QSortFilterProxyModel* levelInfoFilter = new QSortFilterProxyModel(&printSettingDialog);
    levelInfoFilter->setFilterRole(LevelDataProxy::LevelDataRole);
    levelInfoFilter->setFilterFixedString("1");
    levelInfoFilter->setSourceModel(flatModel);

[p3c0]

@VRonin
How about re-implementing filterAcceptsRow in QSortFilterProxyModel and return true or false depending upon source_parent ? For eg. Item 1 and Item 4 has invisible root as their parent but the their children don't.
Just a non educated guess. Haven't tried myself.

[kshegunov]

Another speculative suggestion:
I don't really like the idea of deriving from the identity proxy and then overriding data(), somehow feels wrong. You want to change the structure, not the data. What I'd try if I were you, is to subclass QAbstractProxyModel and do that depth-search like thingy only once, to obtain a QModelIndex for the "parent". After that in the index* methods (especially relevant seems hasIndex()) I'd return invalid model indexes for items that aren't parented to the parent I've stored in the beginning.

I hope that helps.
Kind regards.

[VRonin]

@p3c0 Most views would hide all children if the parent is hidden so you won't be able to achieve a list of children

@kshegunov the overridden data is to store somewhere the level in the original tree before it gets flattened by KDescendantsProxyModel. I know it's ugly and dirty that's why I asked the question. The second part seems pretty much the way to go but since this I need this just to show a combobox I didn't feel like going through building a QAbstractProxyModel from scratch

[kshegunov]

@VRonin said in Smarter way to get a list of children in Tree Model:

the overridden data is to store somewhere the level in the original tree before it gets flattened by KDescendantsProxyModel.

I don't believe you need that. Pushing a tree model to a list/table view should give you list/table with the root-level items (speculation again!). In my mind it should be just enough to "move" the root of the model before giving it to the view.

I didn't feel like going through building a QAbstractProxyModel from scratch

Well, yes, I can see why, but if you think about it, most of your methods should turn out trivial (more or less) - similarly to the identity proxy model.

Kind regards.