How to get list of visible QModelIndex in QAbstrac

Question

Is there any way to get a list of currently visible items in QAbstractItemView? And, if it possible, to receive any notifications about changing of this list.

Upd: I'm asking exactly about QAbstractItemView or QTreeView with non-plain structure, not QTableView.

Upd2: I'm implementing tree view model with checkboxes. I want next behavior (same for checking/uncheking):

• If one of checkbox is checked - then all childs must be checked
• If all child checkboxes are checked - then parent check box should be checked too. And same for parent of parent, and so on...

Check state are monitored/modified by external data source, so I need a mechanism to update all changed children/parents. dataChanged signal is not enough for me because it is very expansive to build a list of all changed QModelIndex for updating. And it is not necessary at all, because all fresh data will be picked from QAbstractItemModel::data.

I found next dirty hack to update all items: emit dataChanged( QModelIndex(), QModelIndex() ); but it's undocumented for invalid indexes.

So, I need a way to force all visible items redraw they content with fresh data.

Answer 1

For QTreeView, the list of visible items can be traversed like this:

QTreeView& tv (yourTreeView);

// Get model index for first visible item
QModelIndex modelIndex = tv.indexAt(tv.rect().topLeft());

while (modelIndex.isValid())
{
    // do something with the item indexed by modelIndex
    ...
    // This navigates to the next visible item
    modelIndex = tv.indexBelow(modelIndex);
}

Answer 2

I think that there are no cases where list of visible items is requred. In case of correct model implementation all items are updated automatically. Hard part of implementation - force children and parents to update. I wrote following code:

bool TreeModel::setData( const QModelIndex &index, const QVariant &value, int role )
case Qt::CheckStateRole:
        {
            TreeItemList updateRangeList;  // Filled with items, in which all childred must be updated
            TreeItemList updateSingleList; // Filled with items, which must be updated
            item->setCheckState( value.toBool(), updateRangeList, updateSingleList ); // All magic there
            foreach ( TreeAbstractItem *i, updateRangeList )
            {
                const int nRows = i->rowCount();
                QModelIndex topLeft = indexForItem( i->m_childs[0] );
                QModelIndex bottomRight = indexForItem( i->m_childs[nRows - 1] );
                emit dataChanged( topLeft, bottomRight );
            }
            foreach ( TreeAbstractItem *i, updateSingleList )
            {
                QModelIndex updateIndex = indexForItem( i );
                emit dataChanged( updateIndex, updateIndex );
            }
        }

Answer 3

i always update whole QAbstractTableModel with:

emit dataChanged(index(0, 0), index(rowCount(), columnCount()-1)); // update whole view

Answer 4

You can get the topleft and bottom right cell by calling:

tableview->indexAt(tableview->rect().topLeft())
tableview->indexAt(tableview->rect().bottomRight())

To get notification of change, reimplement the virtual function of qabstractscrollarea

scrollContentsBy

This function is called when the view port is scrolled. call QTableView::scrollContentsBy and then do whatever you need to.