Change what column of QTreeView displays expand/collapse icon

Question

Qt version 4.8.4

I have a QTreeView that reflects a QAbstractItemModel-derived model. The model provides data in multiple columns. The expand/collapse icon for a row of the view is always displayed in the cell that is in the column that has a logical index of zero, even if that column has been moved so that it has a visual index other than zero.

Is QTreeView compelled to always draw the expand/collapse icon in logical column zero? Can that be customized, either via the QTreeView or the model?

Answer 1

The expand/collapse icon, along with all the other tree branching lines, is indeed compelled to always draw in logical column zero. In Qt/4.8.4/src/gui/itemviews/qtreeview.cpp, in the QTreeView::drawRow() method, it is hardcoded to only call QTreeView::drawBranches() if the headerSection (which contains the logical index of the column) is zero.

void QTreeView::drawRow( QPainter * painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
  ...

  for ( int currentLogicalSection = 0; currentLogicalSection < logicalIndices.count(); ++currentLogicalSection )
  {
    int headerSection = logicalIndices.at(currentLogicalSection);

    ...

    // If the zeroeth logical column, ...
    if ( headerSection == 0 )
    {
      ...

      // ... draw tree branches and stuff.
      drawBranches(painter, branches, index);
    }
    else
    {
      ... 
    }

    ...
  }

  ...
}