Changing headerData in QTreeView depending on selection

gde23

Hi,

i have a QTreeView, that shows some model derived from QAbstractItemModel.
now i want to show different headerData on the TreeView depending on which type of Item in the view is selected.
How do i implement this?

My problem is, that normally MyTreeModel does not know the TreeView and therefore I do not know where to get the selection information from.

I have tried to get the inof directly from the view, which kind of works, however when using a QSortFilterProxyModel it will crash.

QVariant MyTreeModel::headerData(int section, Qt::Orientation orientation, int role) const
{
    if(m_root_item != NULL){
        if (orientation == Qt::Horizontal && role == Qt::DisplayRole){

            // getting the current item from a pointer to the view stored in the model
            // this seems to be kind of a bad idea
            QModelIndex index = m_tree_view->currentIndex();

            if(!index.isValid()){
                return QVariant();
            }
            
            Item* item_selected = static_cast<Item*>(index.internalPointer());
            if(item_selected != NULL){
                std::string value;
                value = item_selected->getHeader(section);
                return QVariant(value.c_str());
            }
        }
    }
    return QVariant();
}

what is the right way to implement this?

Christian Ehrlicher

Why not listening on QTreeView::selectionChanged somewhere and adjust the header data the way you need it?

gde23

@Christian-Ehrlicher Thanks for the hint.

The easiest way to implement this i can imagine atm is something as follows:

A slot in MyTreeView that is called when selection changes.
From there i call the TreeModel::data() for the current index and add a new role to get the headerData from the items.
Then i call setHeaderData for all the columns and store the data in the TreeModel.
This data is returned when headerData() is called.

I guess this will work, however it sound not like the straight forward approach for such a common application?

Christian Ehrlicher

This is also the way I would solve it. But I don't see this as a common situation. I've no application in mind which changes the header based on the current (selected) index ...

VRonin

If you have a working implementation of setHeaderData and headerData in your model you can just:

QObject::connect(treeView->selectionModel(),&QItemSelectionModel::selectionChanged,treeView->model(),[=](const QItemSelection &selected, const QItemSelection &deselected)->void{
const auto selectedIndexes = selected.indexes();
const auto deselectedIndexes = deselected.indexes();
for(auto&& idx : selectedIndexes){
treeView->model()->setHeaderData(idx.column(),Qt::Horizontal,QStringLiteral("%1 Selected").arg(idx.column()));
}
for(auto&& idx : deselectedIndexes ){
treeView->model()->setHeaderData(idx.column(),Qt::Horizontal,QString::number(idx.column()));
}
});