QAbstractProxyModel use with QTreeView

[SergeyK12]

Hi. Im trying to do the following exercise:
Proxy QStandardItemModel into tree representation. First column is a roots for other columns. But Proxy subclassing unexpectedly undocumented and difficult to understand (without doc or examples).

All i got for now is i should properly define parent method (since i dont use internal pointers)

class StandardTreeProxy : public QAbstractProxyModel {

    // QAbstractItemModel interface
public:
    QModelIndex index(int row, int column, const QModelIndex &parent) const
    {
        return createIndex(row, column);
    }

    QModelIndex parent(const QModelIndex &child) const
    {
        auto sourceIndex = mapToSource(child);
        auto proxyIndex = mapFromSource(sourceModel()->index(sourceIndex.row(), 0));

        if(child.row() == proxyIndex.row()) {
            return QModelIndex();
        }

        return proxyIndex;
    }

    int rowCount(const QModelIndex &parent) const
    {
        return  sourceModel()->rowCount() * sourceModel()->columnCount();
    }

    int columnCount(const QModelIndex &parent) const { return 1; }


    // QAbstractProxyModel interface
public:
    QModelIndex mapToSource(const QModelIndex &proxyIndex) const
    {
        int row = std::round(proxyIndex.row() / sourceModel()->columnCount());
        int col = proxyIndex.row() % sourceModel()->columnCount();
        return sourceModel()->index(row, col);
    }


    QModelIndex mapFromSource(const QModelIndex &sourceIndex) const
    {
        int row = sourceModel()->columnCount() * sourceIndex.row() + sourceIndex.column();
        int col = 0;

        if(row == 0) {
            return index(row, col, QModelIndex());
        }

        return index(row, col, createIndex(0, 0));
    }
};

original model

and proxy

Im trying this, but all i got is columnts placed in a rows.
Is it possible?
Should i owerride another method from proxy?

[JonB]

@SergeyK12
Are you aware that in a QStandardItemModel you can create a parent-child hierarchy? E.g. start from https://doc.qt.io/qt-6/qstandarditemmodel.html#details and QStandardItemModel::insertRow(int row, const QModelIndex &parent = QModelIndex()) etc.

So why don't you store your model like that if it's hierarchical?

Unless you mean you start with a QStandardItemModel which is flat and multi-column like the first one, for whatever reason, and want to display that in the second way. For that yes a proxy like yours would be good.

[SergeyK12]

I found out, that rowCount should return count for child row.
So it should be like this

int rowCount(const QModelIndex &parent) const
{
   if(!parent.isValid()) {
       return sourceModel()->rowCount();
   }
   return  sourceModel()->columnCount() - 1;
}

which reveal problems with parents ( now it only 1 row in a view, all paret idx is invalid)

[Christian Ehrlicher]

@SergeyK12 said in QAbstractProxyModel use with QTreeView:

Proxy QStandardItemModel into tree representation.

Why? There is no need for a proxy here at all.

[SergeyK12]

Im not familiar with qt models and proxy, so i found an answer on stackoverflow which stand that proxy is a proper way to do things. I thought its a good point to understand a basic about proxies.

[SergeyK12]

I suppose that mapping function is incorrect (since it direct mapping, without tree structure). QModelIndex::parent crash the app.

    QModelIndex mapToSource(const QModelIndex &proxyIndex) const
    {
        int row = std::round(proxyIndex.row() / sourceModel()->columnCount());
        int col = proxyIndex.row() % sourceModel()->columnCount();
        return sourceModel()->index(row, col);
    }


    QModelIndex mapFromSource(const QModelIndex &sourceIndex) const
    {
        int row = sourceModel()->columnCount() * sourceIndex.row() + sourceIndex.column();
        int col = 0;

        if(row == 0) {
            return index(row, col, QModelIndex());
        }

        return index(row, col, createIndex(0, 0));
    }

[Christian Ehrlicher]

I still don't understand what you're trying to achieve - QStandardItemModel can be used in a QTreeView without any problems. So why trying to create a proxy model for this then? What's the gain?

[SergeyK12]

@Christian-Ehrlicher
Sorry, i cant find a way to show this:

as a tree

without proxy
Possibly a should store data other way or use roles?

[JonB]

@SergeyK12
Are you aware that in a QStandardItemModel you can create a parent-child hierarchy? E.g. start from https://doc.qt.io/qt-6/qstandarditemmodel.html#details and QStandardItemModel::insertRow(int row, const QModelIndex &parent = QModelIndex()) etc.

So why don't you store your model like that if it's hierarchical?

Unless you mean you start with a QStandardItemModel which is flat and multi-column like the first one, for whatever reason, and want to display that in the second way. For that yes a proxy like yours would be good.