Always show QTreeview branches in the far left column

[Nightfox]

I'm working with a Qtreeview and I'm facing some problems having the treview shown when either the first column is hidden or when I rearrange the tree.

I'm using a custom model where I've tried to put in a 'branch column' (m_branchcolumn see below) to map the parent to the first visible column in the treeview but it doesn't work. I always see the treeview nodes (the plus and minus signs) in column zero. I'm using an internal record representation like the nodeitem from the simple treeview example shipped with Qt.

QModelIndex ViewModel::parent(const QModelIndex &child) const
{
    if (!child.isValid())
        return QModelIndex();
 
    Record *rec = recordFromIndex(child);
    if (!rec)
        return QModelIndex();
 
    Record *parentRecord = rec->parent;
    if (!parentRecord)
        return QModelIndex();
 
    if(parentRecord == rootRecord)
        return QModelIndex();
 
    Record *grandparentRecord = parentRecord->parent;
 
    if (!grandparentRecord)
        return QModelIndex();
 
    int row = grandparentRecord->children.indexOf(parentRecord);
    return createIndex(row, m_branchcolumn, parentRecord);
}

QModelIndex ViewModel::parent(const QModelIndex &child) const
{
    if (!child.isValid())
        return QModelIndex();

    Record *rec = recordFromIndex(child);
    if (!rec)
        return QModelIndex();

    Record *parentRecord = rec->parent;
    if (!parentRecord)
        return QModelIndex();

    if(parentRecord == rootRecord)
        return QModelIndex();

    Record *grandparentRecord = parentRecord->parent;

    if (!grandparentRecord)
        return QModelIndex();
    
    int row = grandparentRecord->children.indexOf(parentRecord);
    return createIndex(row, m_branchcolumn, parentRecord);
}

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How can I make sure always to show the tree branches in the far left visible column even after column change and with hidden columns?

[wysota]

By definition QTreeView displays branches in the column with logical index '0' (or the lowest non-hidden column probably but I'm not sure). To override that you have to either provide a proxy model that will rearrange your columns or reimplement QTreeView.

[Nightfox]

Thanks for your reply wysota

By definition QTreeView displays branches in the column with logical index '0' (or the lowest non-hidden column probably but I'm not sure).

Yes, QTreeview displays branches in the column with logical index '0' but if that column is hidden the tree nodes will not appear. Tree effect is preserved however as the user is still able to expand/subtract with plus and minus keys.

To override that you have to either provide a proxy model that will rearrange your columns or reimplement QTreeView.

Acctually I am using a proxymodel for the treeview already. How would I go about rearranging the columns to get the effect I want?

Thanks

[wysota]

The easiest would be to reimplement data() and call the base class implementation of the proxy with a modified index (switched column numbers).

[Nightfox]

This is my reimplementation! I've tried to change the index but as it's a const function all my changes resolves in error. What would I need to change in this data function to swap say column 0 with column 1?

QVariant MyProxyModel::data ( const QModelIndex & index, int role ) const
{
    if (!index.isValid())
        return QVariant();
 
    return QAbstractProxyModel::data(index, role);
}

QVariant MyProxyModel::data ( const QModelIndex & index, int role ) const
{
    if (!index.isValid())
        return QVariant();

    return QAbstractProxyModel::data(index, role);
}

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Thank you again for your help!

[wysota]

Create a new index, don't change the original one (it's const...).

For example:

QModelIndex changed = index.sibling(index.row(), (index.column()+1) % 10);

QModelIndex changed = index.sibling(index.row(), (index.column()+1) % 10);

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[Nightfox]

It definitely one way to go but it gets messy. If I make changes to the 0 column the changes will be saved in the 'swap' column. Eventually I'll have to accommodate this change in index, parent, mapToSource, mapFromSource aswell right?

Below I'm substituting the branch column with 0 column and vica versa.

This is my new implementation;

QVariant MyProxyModel::data ( const QModelIndex & index, int role ) const
{
    if (!index.isValid())
        return QVariant();
 
    if(index.column() == m_branchcolumn)
    {
        QModelIndex changed = index.sibling(index.row(), 0);
        return QAbstractProxyModel::data(changed, role);
    }
    if(index.column() == 0)
    {
        QModelIndex changed = index.sibling(index.row(), m_branchcolumn);
        return QAbstractProxyModel::data(changed, role);
    }
    return QAbstractProxyModel::data(index, role);
}

QVariant MyProxyModel::data ( const QModelIndex & index, int role ) const
{
    if (!index.isValid())
        return QVariant();

    if(index.column() == m_branchcolumn)
    {
        QModelIndex changed = index.sibling(index.row(), 0);
        return QAbstractProxyModel::data(changed, role);
    }
    if(index.column() == 0)
    {
        QModelIndex changed = index.sibling(index.row(), m_branchcolumn);
        return QAbstractProxyModel::data(changed, role);
    }
    return QAbstractProxyModel::data(index, role);
}

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I haven't gotten it to work correctly yet but I think this might be the way forward. Thanks for you input.

[wysota]

It definitely one way to go but it gets messy. If I make changes to the 0 column the changes will be saved in the 'swap' column. Eventually I'll have to accommodate this change in index, parent, mapToSource, mapFromSource aswell right?

It depends on your model.

[Nightfox]

The model is a reimplemented QAbstractProxyModel. This shows you the functions I've reimplemented so far.

virtual int columnCount (const QModelIndex& parent = QModelIndex()) const ;
    virtual int rowCount(const QModelIndex& parent) const ;
 
    virtual QModelIndex index(int row, int column, const QModelIndex& parent = QModelIndex()) const ;
    virtual QModelIndex parent (const QModelIndex& index) const ;
 
    virtual QModelIndex mapFromSource(const QModelIndex&) const ;
    virtual QModelIndex mapToSource(const QModelIndex&) const ;
    virtual bool hasChildren ( const QModelIndex & parent = QModelIndex() ) const;
    virtual QVariant data ( const QModelIndex & index, int role = Qt::DisplayRole ) const;
    virtual Qt::ItemFlags flags ( const QModelIndex & index ) const;

virtual int columnCount (const QModelIndex& parent = QModelIndex()) const ;
    virtual int rowCount(const QModelIndex& parent) const ;

    virtual QModelIndex index(int row, int column, const QModelIndex& parent = QModelIndex()) const ;
    virtual QModelIndex parent (const QModelIndex& index) const ;

    virtual QModelIndex mapFromSource(const QModelIndex&) const ;
    virtual QModelIndex mapToSource(const QModelIndex&) const ;
    virtual bool hasChildren ( const QModelIndex & parent = QModelIndex() ) const;
    virtual QVariant data ( const QModelIndex & index, int role = Qt::DisplayRole ) const;
    virtual Qt::ItemFlags flags ( const QModelIndex & index ) const;

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Surely I need to swao the index for all these functions?

[wysota]

If you are already implementing a proxy model then everything is just a matter of adjusting your mapFromSource() and mapToSource() methods. In the other methods you surely already use those two so everything should work fine.

[Nightfox]

This gets more and more messy! I've implemented this to swap column 0 with the branch column in order to always have the branches in the far left column, even after user column rearrange.

However after the change in mapFramSource and mapToSource no data is displayed in the tree.

QModelIndex MyProxyModel::mapFromSource(const QModelIndex& sourceIndex) const
{
    if (sourceIndex.isValid())
    {
        int key = sourceModel()->data(sourceModel()->index(sourceIndex.row(), m_sourcekeycolumn,QModelIndex()) ).toInt() ;
        Record *rec = internaltable->m_map.value(key);
        int row = 0;
 
        if(rec->parent)
            row = rec->parent->children.indexOf(rec);
        const int brcol =  getBranchColumn();
        if( sourceIndex.column() == brcol ) {
            QModelIndex changed = sourceIndex.sibling(row, 0); //new
            return changed;
        }
        if( sourceIndex.column() == 0 ){
            QModelIndex changed = sourceIndex.sibling(row, brcol ); //new
            return changed;
        }
        return createIndex(row,sourceIndex.column(),rec) ;
    }
    return QModelIndex();
}
//
QModelIndex MyProxyModel::mapToSource(const QModelIndex& proxyIndex) const
{
    if(proxyIndex.isValid())
    {
        Record *rec = recordFromIndex(proxyIndex);
        const int brcol =  getBranchColumn();
        if(rec)
        {
            if( proxyIndex.column() == brcol ) {
                QModelIndex changed = proxyIndex.sibling(proxyIndex.row(), 0); //new
                return changed;
            }
            if( proxyIndex.column() == 0 ){
                QModelIndex changed = proxyIndex.sibling(proxyIndex.row(), brcol ); //new
                return changed;
            }
        }
    }
    return QModelIndex() ;
}

QModelIndex MyProxyModel::mapFromSource(const QModelIndex& sourceIndex) const
{
    if (sourceIndex.isValid())
    {
        int key = sourceModel()->data(sourceModel()->index(sourceIndex.row(), m_sourcekeycolumn,QModelIndex()) ).toInt() ;
        Record *rec = internaltable->m_map.value(key);
        int row = 0;

        if(rec->parent)
            row = rec->parent->children.indexOf(rec);
        const int brcol =  getBranchColumn();
        if( sourceIndex.column() == brcol ) {
            QModelIndex changed = sourceIndex.sibling(row, 0); //new
            return changed;
        }
        if( sourceIndex.column() == 0 ){
            QModelIndex changed = sourceIndex.sibling(row, brcol ); //new
            return changed;
        }
        return createIndex(row,sourceIndex.column(),rec) ;
    }
    return QModelIndex();
}
//
QModelIndex MyProxyModel::mapToSource(const QModelIndex& proxyIndex) const
{
    if(proxyIndex.isValid())
    {
        Record *rec = recordFromIndex(proxyIndex);
        const int brcol =  getBranchColumn();
        if(rec)
        {
            if( proxyIndex.column() == brcol ) {
                QModelIndex changed = proxyIndex.sibling(proxyIndex.row(), 0); //new
                return changed;
            }
            if( proxyIndex.column() == 0 ){
                QModelIndex changed = proxyIndex.sibling(proxyIndex.row(), brcol ); //new
                return changed;
            }
        }
    }
    return QModelIndex() ;
}

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My model hieracy is QStandarItemModel to QAbstractProxyModel to QSortFilterProxyModel so the source model for the treeview is QSortFilterProxyModel. Why can't I squeeze more functionality out of the two extra proxy models to archive the column swap? I had really hoped for more help from one of the proxies!

What an I doing wrong?